(lecture notes in math, no 240)adalbert kerber-representations of permutation groups representations...
TRANSCRIPT
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 1/197
L e c t u r e N o t e s i n
M a t h e m a t i c sA col lect ion of informal reports and seminars
Edited b y A. Dold, Heidelberg and B. Eckm ann, Z(Jrich
240
Adalbert KerberMathematisches Inst i tut der Justus Liebig-Universi t~i t
Giessen/Deutschland
Representat ions of
Permutat ion Groups !
$Springer-Verlag
B e r l i n - He ide lbe r g - N ew York 19 71
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 2/197
AM S Subjec t Class if ica t ions (1970 ) : 20C 30
ISBN 3-540-05693-9 Springer-Vedag Ber l in . H eide lberg - N ew Yo rk
ISB N 0-387-05693-9 Springer-Verlag N ew Yo rk • H eid elb erg . Berl in
Th is work is subject to copyright. All r ights are reserved, wheth er the w hole or par t of the ma terial is concerned,
specifical ly those of t ran slat ion, reprint ing, re-use of i l lus trat ions , broadcast ing, reprod uct ion by pho tocop ying mac hineor s im ilar means , and s torage in data banks .
Un der § 54 of the G erm an Copyright Law where c0 pi ~ ace made for othe r than private use, a fee is payable to the publ isher,the am ount of the fee to b e de te rmined by agreement wi th the publ i sher .
@ by Sptinser-Verlag Berl in : Heidelb erg 1971. Librm of Congress Catalog Card Nu m be r 72-1839~ Printe d in Germany.
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 3/197
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 4/197
P r e f a c e
A s a c o n t r i b u t i o n t o t h e t h e o r y o f r e p r e s e n t a t i o n s o f p e r m u t a t i o n
g r o u p s t h e t h e o r y o f r e p r e s e n t a t i o n s o f w r e a t h p r o d u c t s o f f i n i t e
g r o u p s i s d i s c u s s e d i n t h i s f i r s t p a r t w i t h s u b s e q u en t a p p l i c a t i o n s
t o t h e t h e o r y o f r e p r e s e n t a t i o n s o f s y m m e t r i c a n d a l t e r n a t i n g g r o u p s .
T h e i n t e n t i o n i s to g i v e a n e w d e s c r i p t i o n a n d a f u r t h e r d e v e l o p m e n t
o f t h e r e p r e s e n t a t i o n t h e o r y o f s y m m e tr i c a n d a l t e r n a t i n g g r o u p s a n d
t h i s w i l l b e c a r r i e d o n i n t h e f o l l o w i n g pa r t s . T h i s s e e m s d e s i r a b l e
s i n c e f o l l o w i n g t h e a p p e a r a n c e o f t h e o n l y c o m p r e h e n s i v e t r e a t m e n t o f
t h i s t h eo r y , n a m e l y G . d e B . R o b i n s o n ' s b o o k " R e p r e s e n t a t i o n T h e o r y o f
t h e S y m m e t r i c G r o u p " ( T o r o n t o 1 9 61 ) a n u m b e r o f p a p e r s h a v e b e e n
p u b l i s h e d w h i c h c o n t i n u e d t h i s w o r k . M o r e o v e r s o m e of t h e s e p a p e r s
c o n t a i n r e s u l t s w h i c h a l l o w g e n e r a l i z a t i o n s w h i c h c o n n e c t t h i s t h e o r y
m o r e c l o s e l y w i t h t h e g e n e r a l r e p r e s e n t a t i o n t h e o r y o f f i n i t e g ro u p s .
T h e r e p r e s e n t a t i o n t h e o r y of s y m m e t r i c a n d a l t e r n a t i n g g r o u p s i s
s11mmarized as far as is need ed here, while a kno wle dge of the mai n
r e s u l t s o f t h e g e n e r a l r e p r e s e n t a t i o n t h e o r y o f f i n i t e g r o u p s o v e r
f i e l d s i s a s su m e d .
T h e r e s u l t s o f t h e r e p r e s e n t a t i o n t h e o r y o f t h e s y m m e t r i c g r o u p w h o s e
p r o o f s a r e o m i t t e d h e r e w i l l b e t r e a t e d i n d e t a i l i n t he f o l l o w i n g
parts.
I w o u l d e x p r e s s m y s i n c e r e s t t h ~ n k s t o P r o f . H . B o e r n e r , P r o f . H . K .
F a r a h a t , D r . M .H . P e e l a n d P ro f . G . d e B . R o b i n s o n t o w h o m I a m
g r e a t l y i n d e b t e d f o r v e r y h e l p f u l d i s c u s s i o n s a n d s t i m u l a t i n g
e n c o u r a g e m e n t .
A d a l b e r t K e r b e r
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 5/197
Con t en t s
I n t r o d u c t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . I
C H A P T E R I: W r e a t h p r o d u c t s o f g r o u p s . . . . . . . . . . . . . . . @
I. P e r m u t a t i o n g r o u p s . . . . . . . . . . . . . . . . . . . . . 5
2 . W r e a t h p r o d u c t s . . . . . . . . . . . . . . . . . . . . . .4
3, W r e a t h s w i t h s y m m e t r i c g r o u p s . . . . . . . . . . . . . . . 3 9
C H A P T E R I I: R e p r e s e n t a t i o n s o f w r e a t h p r o d u c t s . . . . . . . . . . 5 9
@ . T h e o r d i n a r y i r r e d u c i b l e r e p r e s e n t a t i o n s o f t h e s y m m e tr i c
g r o u p . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 0
5. R e p r e s e n t a t i o n s o f w r e a t h p r o d u c t s . . . . . . . . . . . . . 8 9
C H A P T E R I I I: A p p l i c a t i o n t o t h e r e p r e s e n t a t i o n t h e o r y o f
s y m m e t r i c a n d a l t e r n a t i n g g r o u p s . . . . . . . . . . . . . . 1 1 @
6 . S y m m e t r i z e d o u t e r p r o d u c t s o f i r r e d u c i b l e C - r e p r e s e n t a t i o n s
o f s y m m e t r i c g r o u p s . . . . . . . . . . . . . . . . . . . . 1 1 6
7. B l o c k - s t r u c t u r e a n d d e c o m p o s i t i o n n u m b e r s o f s y mm e t r i c a n d
a l t e r n a t i n g g r o u p s . . . . . . . . . . . . . . . . . . . 1 3 0
8 . G e n e r a l i z e d d e c o m p o s i t i o n n u m b e r s o f s y m m e tr i c a n d a l t e r n a -
t i n g g r o u p s . . . . . . . . . . . . . . . . . . . . . . . . 1 6 8
References . . . . . . . . . . . . . . . . .
8ubJect-Index . . . . . . . . . . . . . . . . .
. . . . . . . . 82
. . . . . . . . 191
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 6/197
I n t r o d u c t i o n
T h e d e r i v a t i o n o f t h e r e p r e s e n t a t i o n t h e o r y o f w r e a t h p r o d u c t s
p r o v i d e s a n i c e e x a m p l e o f t h e u t i l i t y o f C l i f f o r d ' s t h e o r y o f
r e p r e s e n t a t i o n s o f g r o u ps w i t h n o r m a l d i v i s o r s.
A p p l i c a t i o n s o f t h i s t h e o r y to t h e r e p r e s e n t a t i o n t h e o r y o f s y m -
m e t r i c a n d a l t e r n a t i n g g r o u p s a r i s e f r o m t h e fa c t, t h a t c e n t r a -
l i z e r s o 3 el e m e n t s , n o r m a l i z e r s o f c e r t a i n s u b g r o u p s , S y l o w - s u b -
g r o u p s a s w e l l a s d e f e c t g r o u p s a r e a l l d i r e c t p r o d u c t s o f w r e a t h
p r o d u c t s . T h u s f o r e x a m p l e t h e t h e o r y o f t h e g e n e r a l i z e d d e c o m p o -
s i t i o n n u m b e r s a s w e l l a s t h e t h e o r y o f s y m m e t r i z e d o u t e r p r o -
d m o t s o f i r r e d u c i b l e o r d i n a r y r e p r e s e n t a t i o n s o f s y m m e t r i c g r o u p s
c a n b e d e s c r i b e d w i t h t h e a id o f t h i s t h e o r y .
O n t h e o t h e r h a n d, r e p r e s e n t a t i o n s o f w r e a t h p r o d u c t s w i t h s y m -
m e t r i c g r o u p s c a n b e d e s c r i b e d i n d e t a i l b y u s i n g t h e t h e o r y o f
r e p r e s e n t a t i o n s o f t h e s y m m e t r i c g r o up . B u t n e v e r t h e l e s s t h i s i s
n o v i c i o u s c i r c l e, s i n c e t h e d e g r e e s m o f t h e s y m m e t r i c f a c t o r s
S of the applie d wre ath products G~S satis fy m<n, if n is the
d e g r e e o f t h e c o n s i d e r e d s y m m e t r i c g r o u p S . T h u s o n t h e c o n t r a r y
t h e s e a p p l i c a t i o n s p r o v i d e i n t e r e s t i m g r e c u r s i o n p r o c e s s e s .
B e s i d e s t h i s d e s c r i p t i o n o f r e p r e s e n t a t i on s o f w r e a t h p r o d u c t s
a n d s o m e o f t h e i r a p p l i c a t i o n s s o m e n e w r e s u l t s o n th e m o d u l a r
r e p r e s e n t a t i o n t h e o r y o f s y m m e t r i c a n d a l t e r n a t i n g g r o u p s a r e
c i t e d o r p r o v e d e s p e c i a l l y w i t h r e f e r e n c e t o t h e t h e o r y o f d e c o m -
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 7/197
p o s i t i o n n u m b e r s .
I t s h o u l d b e m e n t i o n e d t h a t w r e a t h p r o d u c t s a r e i n v o l v e d i n s o m e
c o m b i n a t o r i a l a n d g r a p h - t h e o r e t i c a l d e v i c e s a n d t h e n e w i n t e r e s t
o f p hy s i c i s t s s h o u l d n ' t b e f o r g o t t e n ( s ee t h e r e f e r e n c e s ) .
T h e f i r s t e x a m p l e s o f w r e a t h p r o d u c t s c a n b e f o u n d i n A . C a u c h y ' s
I . H 9" E x e r c i s e s d ' a n a l y s e e t d e p h y s i q u e m a t h e m a t l q u e ( v o l I II , 18 4 4 )
i n E . N e t t o ' s " S u b s t i t u t i o n e n t h e o r i e u n d i h r e A n w e n d u n g e n a u f d i e
A l g e b r a " a n d in A . R a d z i g ' s d i s s e r t a t i o n e n t i t l e d " D i e A n w e n d u n g
d e s S y l o w ' s c h e n S a t z e s a u f d i e s y m m e t r i s c h e u n d d i e a l t e r n i r e n d e
G r u p p e " ( 1 8 95 ) . W r e a t h p r o d u c t s a r i s e i n t h e s e c a s e s i n c o n n e c t i o n
w i t h t he c o n s t r u c t i o n o f S y l c w - s u b g r o u p s o f t h e c o n s i d e r e d s y m m e -
t r i c g r o u p .
T h e f i r s t r e p r e s e n t a t i o n - t h e o r e t i c a l c o n s i d e r a t i o n o f w r e a t h p r o -
d u c t s w a s g i v e n b y A . Y o u n g , w h o a p p l i e d h i s m e t h o d o f d e r i v i n g
t h e r e p r e s e n t a t i o n t h e o r y o f t h e s y m m e t r i c g r o u p t o t h e s o - c a l l e d
h y p e r o c t a h e d r a l g r o u p i n 1 9 3 0 ( Y o u n g C I~ ). I n m o d e r n n o t a t i o n t h e
h y p e r o c t a h e d r a l g r o u p i s a w r e a t h p r o d u c t $ 2 ~ S n . W . S p e c h t c o n -
s i d e r e d w r e a t h p r o d u c t s o f t h e m o r e g e n e r a l f o r m G ~ S n ( G a f i n i t e
g r o u p ) i n h i s d i s s e r t a t i o n ( S p e c h t C I ~, 1 9 3 2) a n d d e s c r i b e d t h e i r
o r d i n a r y r e p r e s e n t a t i o n t h e o r y w h i c h h e g e n e r a l i z e d t o p r o d u c t s
o f t h e f o r m G ~ H ( G c o m p l e t e l y r e d u c i b l e , H a s u b g r o u p o f S ) i n
1 9 3 3 ( S p e o h t E 2 ~ ) .
S u c h g r o u p s h a d a l r e a d y a p p e a r e d i n p a p e r s o f A . L o e w y ( L o e w y E I~ ,
1 9 2 7 ) , A. S c h o l z ( S c h o l z ~ I~ , 1 9 3 0) a n d B . N e u m a n n ( N e u m a n n ~ I ~ ,
1 9 32 ) . I n h i s p a p e r " K o m b i n a t o r i s c h e A n z a h l b e s t i m m u n g e n f G r G r u p -
p e n , G r a p h e n u n d c h e m i s c h e V e r b i n d u n g e n " G . P o l y a s u g g e s t e d f o r
G ~ H t h e n a m e " G - K r a n z u m H" , o f w h i c h " G - w r e a t h a r o u n d H " i s a
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 8/197
3
t r a n s l a t i o n . W r e a t h p r o d u c t s G ~ S w e r e a l s o c o n s i d e r e d b y O . O r e
(Ore [1 ] ) and by R. Pz~oh t (~zmch t [1 ] ) i n 1942.
S i n c e t h e n n u m e r o u s p a p e r s o n t h e s e g r o u p s a s w e l l a s o n t h e
r e p r e s e n t a t i o n t h e o r y o f s p e c i a l c a s e s h a v e b e e n p u b l i s h e d ( s ee
t h e p a p e r s o f O e i m a, P u t t a s w a m a i a h , K e r b e r ) $ r e f e r e n c e s t o s o me
a p p l i c a t i o n s t o c o mb i n a t o r i c s , g r a p h t h e o r y a n d p h y s ic s m a y be
f o u ~ a t t h e en d o f t h e s e n o t e s.
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 9/197
C h a p t e r I
W r e a t h p r o d u c t s o f gr o u p s
I n t h e f i r s t s e c t i o n , b y w a y o f f i x i n g t h e n o t a t i o n , w e g i v e
r e s u l t s c o n c e r n i n g t h e s y m m e t r i c g r o u p S ( ~ C l } ~ S ~ S n ~ C l ] )
a n d t he a l t e r n a t i n g g r o u p A ( ~ [ I ] ~ n ~ A n ~ [ 1 ] ) . I n t h e s e c o nd
s e c t i o n g e n e r a l w r e a t h p r o d u c t s G ~ H a r e i n t r o d u c e d a n d i n th e
t h i r d s e c t i o n a t t e n t i o n i s r e s t r i c t e d t o w r e a t h p r o d u c t s G ~ H w i t h
H = S n a n d G a f i n i t e g r o u p .
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 10/197
I. P e r m u t a t i o n g r o u p s
A b i j e c t i v e m a p p i n g o f a s e t 6 o n t o i t s e l f i s c a l l e d a p e r m u t a t i o n
o_~f 6 . I f a s e t o f p e r m u t a t i o n s o f a s e t 6 t o g e t h e r w i t h t h e c o m -
p o s i t i o n m u l t i p l i c a t i o n i s a g r o u p, w e c a l l t h i s g r o u p a p e r m u -
t a t i o n g r o u p o n G . T he g r o u p S G o f a l l t h e p e r m u t a t i o n s o f 6 i s
c a l l e d t h e s , y mm e tr i c g r o u p o n 6 .
T h e s y m m e t r i c g r o u p s o n t w o f i n i t e s e t s 6 ' a n d 6 " o f t h e s a m e
o r d e r n = 1 6' I = I G " I a r e o b v i o u s l y i s o m o r p h i c . H e n c e w e m a y d e -
n o t e t h e s y m m e t r i c g r o u p s o f f i n i t e s e t s 6 o f o r d e r I~I = n b y
S a n d a s s u m e t h a t 6 = ~ 1 , . . . , n ~ . T h e e l e m e n t s o f 6 a r e c a l l e d
s y m b o l s .
T h e o r d e r o f S
1.1
is
I S n l = n !
a s i s w e l l k n o w n . S u b g r o u p s o f S a r e c a l l e d p e r m u t a t i o n g r o u p s
o f d e ~ r e e n; t h e i r e l e m e n t s a r e c a l l e d p e r m u t a t i o n s o f d e g r e e n .
A p e r m u t a t i o n ~ E S ( o n 6 = ~ 1 , . . . , n ~ ) i s w r i t t e n d o w n i n f u l l
b y p u t t i n g t h e i m a g e s ~ ( i ) i n a r o w u n d e r t h e s y m b o l s i E G , f o r
e x a m p l e
f o r s h o r t :
1 n
( i l=
•
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 11/197
I n a c c o r d w i t h t h e n o t a t i o n ~ ( i) f o r t h e i m a g e o f t h e s y m b o l i
u n d e r t h e p e r m u t a t i o n ~ , p r o d u c t s o f p e r m u t a t i o n s h a v e t o b e re a d
f r o m t h e r i g h t t o t h e l e f t :
: = .
F o r s u b s e t s ~ ' E Q l e t
: = I
A p e r m u t a t i o n o f t h e f o r m
( ix i2 "'" ir-X i r ir+1 "ii in )
i i ..- i i Jr + I - i
i s c a l l e d c y c l i c o r a c y c le . T o e m p h a s i z e t h e n u m b e r o f s y m b o l s
w h i c h a r e m o v e d b y t h i s c y c l e , w e c a l l i t a n r - c y c l e . M o r e b r i e f l y
w e w r i t e
( i l . . - i ) ,
w h e r e t h e l - c y c l e s ( J r + l ), . . . , ( in ) o n t h e s y m b o l s w h i c h r e m a i n
f i x e d h a v e b e e n o m i t t e d .
T h e i d e n t i t y e l e m e n t o f S n, t h e p e r m u t a t i o n w h i c h c o n s i s t s o n l y
o f l - c y c l e s w i l l b e d e n o t e d b y I o r b y I Sn .
T h e f o l l o w i n g i s o b v i o u s l y v a l i d :
1 . 2 ( i l . . . i r ) = ( i 2 . . . i r i I ) . . . . . ( i r i l . . . i r _ I ) •
T h i s m e a n s t h a t a c y c l e w h i c h a r i s e s f r o m a g i v e n o n e b y c y l i c a l -
l y p e r m u t i n g t h e s y m b o l s d e s c r i b e s t h e s a m e p e r m u t a t i o n .
2 - c y c l e s , i .e . p e r m u t a t i o n s w h i c h m o v e e x a c t l y t w o s y m b o l s o f ~,
a r e c a l l e d t r a n s p o s i t i o n s .
T h e o r d e r o f a c yc l e , i . e. t h e o r d e r o f t h e g e n e r a t e d c y c l i c
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 12/197
s u b g r o u p < ( i l . . . i r ) > ~ S n, i S e q u a l t o i t s l e n g t h :
1 . 3 l < ( i l . . . i r ) > I = r .
T h e i n v e r s e o f t h i s c y c l e i s
1 . 4 ( i l . . . i r ) - I = ( i r i r _ 1 . . . i I ) •
D i s j o i n t c y c l e s ( i .e . t h e s e t s o f r e a l l y m o v e d s y m b o l s a r e d i s -
j o in t ) d e s c r i b e c o ~ u t i n g p e r m u t a t i o n s . E a c h p e r m u t a t i o n c a n b e
w r i t t e n i n c y c l e - n o t a t i o n , i . e . a s a p r o d u c t o f p a i r w i s e d i s j o i n t
c y c l e s , w h i c h a r e u n i q u e l y d e t e r m i n e a - a s p e r m u t a t i o n s ( cf . 1 . 2)
- u p t o t h e i r e r d e r o f o c c u r e n c e .
B e c a u s e o f
1 . 5 ( i l . . . i r ) = ( i l i r ) ( i l i r _ 1 ) . . . ( i l i 2 )
e a c h c y c le , a n d t h e r e f o r e e v e r y p e r m u t a t i o n , t o o , c a n b e w r i t t e n
a s a p r o d u c t o f t r a n s p o s i t i o n s . H e n c e S i s g e n e r a t e d b y t h e
t r a n s p o s i t i o n s .
S i n c e
1 . 6 ( l j , i k + 1 ) = ( i k , i k + 1 ) ( i j i k ) ( i ~ , i ~ + ~ )
S i s g e n e r a t e d e v e n b y t h e t r a n s p o s i t i o n s o f s u c c e s s i v e s y m b o l s .
A n o t h e r s y s t e m o f g e n e r a t o r s o f S i s ~ ( 1 2 ) , ( 1 2 . . . n ) S , f o r
1 . 7 ( 1 . . . n ) r ( s 2 ) ( 1 . . . n ) - r = ( r + 1 , r + 2 ) , 0 _( r( n- 2 .
H e n c e
! ~ S = ( ( 1 2 ) , ( 2 3 ) , . . . , ( n - l , n ) ) = ( ( 1 2 ) , ( I . . . n ) ~ .
( F o r f u r t h e r r e s u l t s o n s y s t e m s o f g e ne r a t o r s c o m p a r e O o x e t e r /
M o s e r K I S, P i c c a r d C I S - C 3 S. )
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 13/197
W e w o u l d l i k e n o w t o d e s c r i b e t h e c o n j u g a c y c l a s s e s o f S n .
T h e o r d e r e d l e n g t h s a l, . .. , a ( ~ j ~ j + 1 ) o f t h e c y c l i c f a c t o r s o f
E S ( w i t h r e s p e c t t o t h e c y c l e - n o t a t i o n o f ~ a n d i n c l u d i n g th e
l e n g t h s o f l- c y c l e s ) f o r m a p a r t i t i o n
1 . 9 P ~ : = ( a l , . . . , e h ) =
o f n , i . e. t h e y s a t i s f y
1 . 1 0 ~ ~ i = n , ~ i E ~ , a j A a j + I ( 1 ~ j < n - S ) .
IP ~ i s c a l l e d t h e p a r t i t i o n o f ~ .
I f ~ i s t h e p a r t i t i o n o f ~, t h e n w e o b t a i n f r o m 1 . 3 t h a t t h e o r -
d e r of t h e g e n e r a t e d s u b g r o u p < ~ > ~ S i s e q u a l t o t h e l e a s t c o m -
m o n m u l t i p l e o f t h e e l e m e n t s a o f ~:
1 . ! 1 P ~ = ( ~ l , . . . , a h ) ~ I <~ >I = I c m ~ i "
T h u s w e h a v e a c r i t e r i o n w h e t h e r ~ i s p - r e g u l a r , p r s i n g u l a r o r a
p - e l e m e n t w i t h r e s p e c t t o a p r i m e n u m b e r p ( i . e. w h e t h e r p t I < ~> I,
P I I<~>l or I<~>I is a po we r of p):
I f P ~ = ( ~ 1 , . . . , ~ n ) :
( i) ~ i s p - r e g u l a r o
( i i) ~ i s p - s i n g u l a r
( i i i ) ~ i s a p - e l e m e n t o
Vi: p t ~i '
~i: p I a ,
V i : ~ i s a p o w e r o f p .
N o w w e w i s h t o s h o w t h a t e a c h s u b s e t o f S c o n s i s t i n g o f t h e p e r -
m u t a t i o n s w i t h a c e r t a i n p a r t i t i o n ~ f o r m s a c o n j u g a c y c l a s s o f
S n . T o p r o v e t h i s w e n o t i c e f i r s t t h a t
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 14/197
i ) (
1 .1 3 ~ , ~ - 1 = ( ~( ~) ) ( ~ ' ( i ) ) ( ~ ) = ' ~ ' ( i ) ) •
T h i s m e a n s, t h a t w e o b t a i n ~ , ~ - 1 f r o m ~' b y a n a p p l i c a t i o n o f
to the symbol s in the cycl e-no tati on of ~', e.g.
(12 3)(3 5)( 123 ) -1 = (15) •
T h i s a p p l i c a t i o n o f ~ o b v i o u s l y d o e s n ' t d i s t u r b t h e l e n g t h s o f t h e
cycli c factors of ~' so that we have
p ~ , ~ - 1 = p ~, .
H e n c e a c o n j u g a c y c l a s s c o n s i s t s o f p e r m u t a t i o n s o f e q u a l p a r t i -
tions.
On the other hand, if we are given ~" E S wit h P~" = P~', there
o b v i o u s l y ex i s t p e r m u t a t i o n s ~ w h i c h f u l f i l ~ , - I = ~ ., n a m e l y
a l l t h e p e r m u t a t i o n s ~ w h i c h m a p t h e s y m b o l s o f ~ ' o n t o t h e s y m -
b o l s o f ~ " a s d e s c r i b e d a b o v e . T h e r e f o r e d e n o t i n g b y ,N, ' t h a t t h e
t w o p e r m u t a t i o n s a r e c o n j u g a t e s w e h a v e
~i N ~" o P~' = P~" .
B e c a u s e o f 1 . 4 w e h a v e P ~ = p ~ - 1 s o t h at e v e r y p e r m u t a t i o n i n
S i s a c o n j u g a t e of i ts i nv e r s e . G r o u p s i n w h i c h e v e r y e l e m e n t
i s a c o n j u g a t e o f i t s i n v e r s e a r e c a l l e d a m b i v a l e n t . H e n c e :
I _ ~ S i s a m b i v a le n t .
T h e u s e o f a s e c o n d n o t a t i o n f a c i l i t a t e s t h e c a l c u l a t i o n o f th e
o r d e r o f a c o n j u g a c y c l a s s. ~ o r i = 1 , . . . , n l e t a i b e t h e n u m b e r
of elem ents ~j of ~ = P~ wit h ~j = i, i.e. the num ber of i-cycle s
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 15/197
1 0
a m o n g t h e c y c l i c f a c t o r s o f ~. T h i s e s t a b l i s h e s a o n e - t o - o n e c o r -
r e s p o n d e n c e b e t w e e n t h e p a r t i t i o n s P ~ = • a n d t h e ( 1 × n ) - m a t r i c e s
1 . 1 6 T ~ : = ( a l , . . . , a n ) = a , O < a i E Z , E i a i = n .-- i
T ~ i s c a l l e d t h e t y p e o f ~ .
H e n c e w e m a y d e s c r i b e t h e c o n J u g a c y c l a s s e s o f S w i t h t h e a i d
o f s u c h n - t u p e l s , t o o : L e t C a = C a d e n o t e t h e c l a s s o f t h e p e r m u -
t a t i o n s o f S c o n s i s t i n g o f h c y c l e s o f t h e l e n g t h s ~ 1 ' " ' '' m h
r e s p e c t i v e l y c o n s i s t i n g o f a i i - c y c l e s f o r i = 1 , . . . , n .
B e c a u s e o f 1 .1 3 a n d 1 . 2 , f o r ~ ' a n d ~" c u t o f C w e h a v e e x a c t l y
a i1.17 ~ i ai!
p e r m u t a t i o n s ~ w h i c h s a t i s f y ~ , ~ - I = ~,,. H e n c e 1 . 1 7 is t h e o r d e r
o f t h e c e n t r a l i z e r C S n ( ~ ' ) o f ~ ' i n S a n d w e h a v e :
a i a iI c = o a l : n , l ( ~ i a l , ) , l % n ( : ' ~ C a ) l : ~ i a , .
A s a n e x a m p l e w e c o n s i d e r S 3 ( f o r n ~ 3 , S i s n o t a b e l i a n ) :
S 3 = { I , ( 1 2 ) , ( 1 3 ) , ( 2 3 ) , ( 1 2 3 ) , ( 1 3 2 ) 3 .
T h i s g r o u p c o n s i s t s o f 3 c o n j u g a c y c l a s s e s c o r r e s p o n d i n g t o t h e
p a r t i t i o n s ( 3 ), ( 2 , 1 ) a n d ( 1 , 1 , 1 ) = : (I 3 ) r e s p e c t i v e l y t o t h e
t y p e s ( O , O , 1 ) , ( 1 , 1 , 0) a n d ( 3 , 0 , 0 ) . T h e s e c l a s s e s a r e
c ( 1 3 ) = c ( 3 , o , o ) = { i ] ,
0 ( 2 ' 1 ) = 0 ( 1 ' 1 ' 0 ) = { ( 1 2 ) , ( 1 3 ) , ( 2 3 ) 3 ,
c (3) = o (°,°,1) = { (1 23) , (1 32) ] .
W e s h a l l c o n s i d e r t h e g r o u p - t h e o r e t i c a l s t r u c t u r e o f t h e c e n t r a -
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 16/197
11
l i z e r s l a t e r o n .
O t h e r s u b g r o u p s o f i m p o r t a n c e a r e t h e a l t e r n a t i n g g r o u p s A n -
A n ~ S c o n s i s t s o f t h 8 p e r m u t a t i o n s ~ E S , w h i c h d o n ' t c h a n g e
t h e s i g n o f t he d i f f e r e n c e - p r o d u c t
~ n ' = 1 7 ( J - i ) ,l< i< j <_n
i . e .
1 . 1 9 A n ' = [ = ~ S n I ~ n : = 1 " I ( ~ ( J ) - ~ ( i ) ) = a n ]l ~ i < j < . . n
( I t is e a s y t o s e e t h a t ~ A n = ~ n ) . R e c a l l t h a t t h e e m p t y d i f f e -
r e n c e - p r o d u c t A I is I b y c o n v e n t i o n s o t h at
A I = A 2 = [1] .
P e r m u t a t i o n s ~ E S n \ A n , i . e. p e r m u t a t i o n s s a t i s f y i n g ~ A n = - A n ,
a r e c a l l e d o d d p e r m u t a t i o n s , t h e e l e m e n t s o f A n a r e c a l l e d e v e n
p e r m u t a t i o n s .
I t i s o b v i o u s , t h a t t h e p r o d u c t o f t w o e v e n p e r m u t a t i o n s i s e v e n,
h e n c e A n i s a s u b g r o u p . T h u s e v e r y p e r m u t a t i o n g r o u p P ~ S c o n -
t a i n s a s u b g r o u p P + c o n s i s t i n g o f i t s e v e n e l e m e n t s :
1 .20 P + == P Q A •
D e p e n d i n g o n ~ , l e f t c o a s t s ~ P + c o n s i s t e i t h e r o f e v e n o r of od d
p e r m u t a t i o n s . S i n c e t h e l e f t c o s e t P + i n c l u d e s a l l t h e e v e n p e r -
m u t a t i o n s w e o b t a i n f o r t h e i n d e x o f P + i n P :
1 ~ I P = P * I ~ 2
H e n c e P + i s a n o r m a l d i v i s o r o f P i n a n y c a s e : P + d P.
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 17/197
12
P o r m ~ 2 S c o n t a i n s t h e t r a n s p o s i t i o n ( 12 ) , w h i c h i s o d d, t h u s w e
o b t a i m a s a s p e c i a l c a s e o f 1 . 2 1:
1 2 2 I A n l = n , / 2 , v
S i n c e 1 . 5 i s v a l i d , a c y c l e i s e v e n i f a n d o n l y i f i t s l e n g t h r
is odd. E. g.
A 3 = [1 ,( 12 3) ,( 13 2) 3 4 S 3 .
H e n c e a n i n v e s t i g a t i o n o f t h e p a r t i t i o n o r o f th e t y p e o f ~ a l l o w s
o n e t o d e c i d e w h e t h e r ~ b e l o n g s t o A n o r t o S n \ A . H e n c e t h e
c o n j u g a o y c l as s e s o f S - l e t ' s c a l l t h e m ~ n - c l a s s e s - b e l o n g to
A n o r t o S n \ A i n f u l l . T h e q u e s t i o n a r i s e s , w h i c h o f t h e S n - c l a s -
s e s s p l i t i n t o ~ n - c l a s s e s .
T h e c e n t r a l i z e r o f a n e v e n p e r m u t a t i o n ~ i n A n i s
(~) = = ( ~ ) G A n •C A n C S n ( ~ ) + O S
H e n c e w e o b t a i n f r o m 1 . 2 1 :
V ~ E A n : e i t h e r C A n ( ~ ) = O S n ( ~ ) o r I C S n ( ~ ) : C A n ( ~ ) I = 2 .
T h u s w e h a v e f o r t h e o r d e r s o f t h e c o n j u g a c y c l a s s e s ( w h i c h a r e
e q u a l t o t h e i n d e x o f t h e c e n t r a l i z e r o f e a c h o f t h e i r e l e m e n t s ) :
¥ ~ E A n : e i t h e r I O S (~ ) I = 2 1 c A ( ~ ) I o r C S ( ~ ) = c A ( ~ ) .
H e n c e t h e S n - c l a s s o f ~ E A s p l i t s - a n d t h e n i n t o t w o A n - c l a s s e s
o f t h e s a m e o r d e r - i f a n d o n l y i f
C A ( ) = C a n •
W e p r o v e a l i t t l e b i t m o r e :
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 18/197
13
F o r n ~l e x a c t l y t h o s e S n - c l a s s e s s p l i t ( a nd t h e n i n t o t w o
c l a s s e s o f e q u a l o r d e r ) , t h e c e n t r a l i z e r s o f w h o s e e l e m e n t s
f u l f i l
C S n ( ) = c A n ( ) •
T h e s e a r e e x a c t l y t h e c l a s s e s t h e p a r t i t i o n s o f w h o s e e l e -
m er it s a r e o f t h e f o r m m = ( ~ 1 , . . . , ~ h ) w i t h p a i r w i s e d i f f e -
r e n t a n d o d d e l e m e n t s m i "
P r o o f : I t r e m a i n s t o p r o v e t h e s e c o n d p a r t o f t he s t a t e m e n t .
a ) A p e r m u t a t i o n ~ c o m m u t e s w i t h e a c h o f i t s c y c l i c f a c t o r s .
H e n c e i f t h e c l a s s o f ~ s p l i t s , ~ c a n n o t h a v e a n o d d c y c l i c
f a c t o r ( of e v e n l e n g t h ) .
A n a l o g o u s l y w e s e e t h a t ~ c a n n o t h av e t w o c y cl i c f a c t o r s
(il...ir) and (i~...i~) of the same odd len gth r, for this
w o u l d i m p l y t h e e x i s t e n c e o f a n o dd p e r m u t a t i o n i n t h e c e n -
t r a l i z e r :
S n \ A n 9 ( i l l ~ ) . . . ( i r i ~ ) E C S n (~ ) •
I t f o l l o w s t h a t a t m o s t t h o s e c l a s s e s s p l i t w h o s e p e r m u t a t i o n
h a s p a i r w i s e d i f f e r e n t a n d o d d e l e m e n t s a i .
b ) T h a t t h e s e c l a s s e s r e a l l y s p l i t w e d e r i v e f r o m t h e o dd o r d e r
~ i o f t h e c e n t r a l i z e r s o f t h e i r e l e m e n t s w h i c h i m p l i e s
+ •
C g n = C S n
q . e . d .
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 19/197
1 4
I f t h e S n - c l a s s C = 0 s p l i t s w e s h a l l deno t e b y C = G ~ t h e
t w o A n - c l a s s e s a n d f i x C a + = C a + b y
( 1 . . . a l ) ( a l + l . . . a l + a 2 ) . . . ( . . . n ) E C a + = C a + ..24
T h o u g h
0 ( 3 ) + = [ ( 1 2 3 ) } , 0 ( 3 ) - = { ( 1 3 2 ) ] ,
i t i s n o t t r u e i n g e n e r a l t h a t O a - c o n s i s t s o f t h e i n v e r s e s o f
t h e e l e m e n t s o f C a + . E . g .
( 2 5 ) ( 3 4 ) ( 1 2 3 4 5 ) ( 2 5 ) ( 3 4 ) = ( 1 5 4 3 2 ) = ( 1 2 3 4 5 ) - 1 ,
s o t h a t ( 1 2 3 4 5 ) a s w e l l a s ( 1 2 3 4 5 ) - 1 b e l o n g t o C ( 5 ) + c A 5 .
W e p r o v e t h a t ( B e r g g r e n [ 1 ] ) :
I ~ A 1 = _ A 2 = [ 1 ] , A T , A 6 , A I O a n d A 1 4 a r e t h e o n l y a m b i v a l e n t
a l t e r n a t i n g g r o u ps .
P r o o f : B e c a u s e o f 1 . 1 5 a n d 1 . 2 3 w e n e e d o n l y c o n s i d e r A n - C l a s s e s
C a ± o f p a r t i t i o n s ~ = ( a l , . . . , C h ) w i t h p a i r w i s e d i f f e r e n t a n d
odd S1~mmELnds a i. E a c h o f t he o t h e r A n - c l a s s e s c o n t a i n s w i t h a n
e l e m e n t i t s i n v e r s e .
L e t
= ( i l . . . i r ) . . . ( j l . . . J s)
b e a p r o d u c t o f d i s j o i n t c y c l e s o f o d d l e n g t h s . W e c a n f o r m
: = ( i 2 i r ) ( i 3 i r _ S ) . . . ( J 2 J s ) ( J 3 J s _ 1 ) . . . ,
t h e s t a n d a r d - ~ o n j u ~ a t o r o f ~ w h i c h s a t i s f i e s
-1 -1 (p ~ p = ~ •
W e n o t i c e , t h a t p i s a n o dd p e r m u t a t i o n i f a n d o n l y i f t h e h u m -
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 20/197
15
h e r o f c y c l i c f a c t o r s o f ~ w h o s e l e n g t h i s c o n g r u e n t 3 m o d u l o @
is odd.
a) I f t h e s t a n d a r d - c o n j u g a t o r p f o r s u c h a n e l e m e n t ~ o ut o f a
s p l i t t i n g c l a s s i s o d d, t h e n t he c o n s i d e r e d a l t e r n a t i n g g r o u p
A c a n n o t b e a m b i v a l e n t . P o r if a E A a n d a ~ - I = - I e q u a t i o n
( I) w o u l d i m p l y ( a - l p ) ~ ( a - l p ) - 1 = ~, w h i c h i s i n c o n t r a d i c t i o n
t o C S n ( ~ ) = C A n ( ~ ) s i n c e a - l p E S n \ A .
b ) I t r e m a i n s t o s h o w t h a t e x a c t l y f o r t h e n a t u r a l n u m b e r s
n ~ [ 1 , 2 , 5 , 6 , 1 0 , 1 4 ] t h e r e a re p a r t i t i o n s w i t h p a i r w i s e d i f f e -
r e n t a n d o d d s u m m a n d s u i a n d s o t h a t t h e n u m b e r o f u i s a t i s -
fy in g ui ~ 3 (4) is odd.
( i ) T h e o n l y p a r t i t i o n s u o f t he n E [ 1 , 2 , 5 , 6 , 1 0 , 1 4 ] w i t h p a i r w i s e
d i f f e r e n t a n d o d d e l e m e n t s = i a r e a s f o l l o w s :
n = 1 : ( 1 ) ; n = 2 : ~ ; n = ~ ,: ( 5 ) ; n ~ , 6 , : ( 5 , 1 ) ; n = 1 0 : ( 9 , 1 ) ,
(7,3); n = 14: (13,1), (11,3), (9,5),
i n e a c h of w h i c h t h e n u m b e r o f e l e m e n t s c o n g r u e n t 3 m o d u l o 4
i s 0 o r 2 a n d t h e r f o r e e v e n . H e n c e t h e s t a n d a r d - c o n j u g a t o r
i s e v e n i n e v e r y c a s e s u c h t h a t t h e s e a l t e r n a t i n g g r o u p s a r e
a m b i v a l e n t .
( i i ) L e t u s n o w l o o k a t t h e n ~ { 1 , 2 , 5 , 6 , 1 0 , 1 4 ] .
W e d i s t i n g u i s h t h e n a t u r a l n u m b e r s n w i t h r e s p e c t t o t h e i r
r e s i d u e c l a s s e s m o d u l o 4.
I . n = 4 k , k E ~ : F o r n = 4 w e h a v e t h e p a r t i t i o n ( 3 , 1 ) a n d
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 21/197
16
f o r k >l t h e p a r t i t i o n ( 4 k - 3 , 3) w i t h a n o d d n u m b e r o f e le -
m e n t s c o n g r u e n t 3 m o d u l o 4 .
2 . n = 4 k + I : B e c a u s e o f t h e a m b i v a l e n c y o f A I a n d A 5 w e a s s u m e
k ~ 2 . ( 4 k - 3 , 3 , 1 ) f u l f i l s t h e c o n d i t i o n .
3 . n = 4 k + 2, k A 4 ( A 2 , A 6 , A S O , A 1 4 a r e a m b i v a l e n t ) : ( 4 ( k - I ) - 3,
5 , 3 , 1 ) .
4. n = 4 + 3: (n) = (4k + 3) has o ne ele men t, and th is o ne is
c o n g r u e n t 3 m o d u l o 4.
T h u s e a c h o f t h e a l t e r n a t i n g g r o u p s A n w i t h n ~ ( 1 , 2 , 5 , 6 , 1 0 , 1 4 S
p o s s e s s e s a c o n j u g a c y c l a s s w h i c h d o e s n o t c o n t a i n t h e i n v e r s e o f
e a c h o f i t s e l e m e n t s a n d h e n c e t h e s e a l t e r n a t i n g g r o u p s a r e n o t
a m b i v a l e n t .
q . e . d .
~ r o m t h e p r o o f o f 1 . 2 5 w e g e t :
1 . 2 6 T h e t w o A n - c l a s s e s C ~ i n t o w h i c h t h e S n - c l a s s t o t h e p a r t i -
t i o n a = ( ~ l , .. . , ~ h ) w i t h p a i r w i s e d i f f e r e n t a n d o dd e l e m e n t s
~ i s p l i t s ( s u p p o s e n > 1 ) a re a m b i v a l e n t i f a n d o n l y i f t h e
n u m b e r o f e l e m e n t s ~ i o f ~ w i t h ~ i ~ 3 ( 4) i s e v e n .
W e s h a l l c o m e b a c k t o th e c e n t r a l i z e r s o f e l e m e n t s w h e n w e h a v e
s a i d s o m e t h i n g a b o u t w r e a t h p r o d u c t s , s i n c e t h e y a r e d i r e c t p r o -
d u c t s o f c e r t a i n w r e a t h p r o d u c t s .
T o c o n c l u d e t h i s s e c t i o n l e t u s l o o k a t t h e d o u b l e c o s e t s o f d e r
c e r t a i n s u b g r o u p s w h i c h w i l l b e o f u s e l a t e r o n.
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 22/197
17
A . J. C o l e m a n h a s p o i n t e d t o t h e s e d o u b l e c o s e t s ( C o l e m a n [ I S ) a s
e l u c i d a t i n g t h e g r o u p - t h e o r e t i c a l b a c k g r o u n d o f t h e a p p a r e n t l y
p u r e l y c o m b i n a t o r i a l i n t r o d u c t i o n t o th e r e p r e s e n t a t i o n t h e o r y
of the symmet ric gr oup (cf. secti on 4).
For a par tit ion ~=(~1, ...,~ h) of n, let gV, ..., ~ be pair wise
d i s j o i n t s u b s e t s o f o r d e r s l ~ I = ~ i of t h e s e t ~ = [ 1 , . . . , n } o f
s y m b o l s o n w h i c h S a c t s .
S u b g r o u p s o f t h e f o r m
1.2 7 S~ := S~I × ... × S~ h = ×i S~ i ~ Sn
( S a i th e s u b g r o u p o f t h e a i! p e r m u t a t i o n s f i x i n g t h e s y m b o l s o u t
o f ~ \ G ~ , 1 ~ i~ h ) a r e c a l l e d Y o u n g - s u b g r o u p s i n h o n o u r o f
A . Y o u n g ( 1 8 7 3 - 1 9 4 0 ) t o w h o m w e a r e i n d e b t e d f o r t h e t h e o r y o f
r e p r e s e n t a t i o n s o f t he s y m m e t r i c g r o u p i n w h i c h s u c h s u b g r o up s
p l a y a n i m p o r t a n t r o l e ( cf . s e c t i o n 4 ) .
I f w e a r e g i v e n t w o p a r t i t i o n s , s a y ~ = ( ~ l , . . . , ~ h ) a n d ~ =
( ~ 1 , . . . , ~ k ) , o f n a nd t w o Y o u n g - s u b g r o u p s S ~ = × S a i a n d S ~ =
× S ~j , ~ a n d ~ * o u t o f S , w e w a n t t o s h o w t h e f o l l o w i n g ( C o l e -
ma n [1 ]) :
P r o o f :
(i) If ~ = ~'~*~'~, ~' E Sa, ~" E S~, we hav e ~ = ~ ' ~ * ~ , Vj.
~ i N ~ Q = ( Q i N ~ * a ), V i , j .
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 23/197
1 8
(ii) I ~ n ~ 1 = I ~ i n ~ * ~ I , v i , j , implies t h a t t h e s u b s e t s
~ i N ~ Q a s w e l l a s t h e s u b s e t s ~ N ~ * ~ f o r m f o r f i x e d j
t w o c o m pl e t e d i s s e c t i o n s o f g ~ i n t o p a i r w i s e d i s j o i n t s u b s e t s
~ * g ~ ) o fh i c h c a n b e c o l le c t e d i n to p a i r s ( ~ N ~ ' ~ i N
s u b s e t s o f e q u a l o r d e r .
H e n c e f o r e a c h i t h e r e i s a ~ E S a i s a t i s f y i n g
, a ~ g ~ ) = g ~ N ,~ i ( D i G ~ * g ~ V J .
M u l t i p l y i n g t h e s e ~ t o g e t h e r w e h a v e f o r t h e r e s u l t i n g
~' ~ = ~ . . . ~ ~ s ~
T h u s t h e r e i s a ~ " £ S ~ s u c h t h a t ~ = ~ , - I ~ . ~ , , a s s t a t e d .
q . e . d .
H e n c e w e h a v e a l - I - c o r r e s p o n d e n c e b e t w e e n t h e s e t o f d o u b l e c o -
s e t s S u ~ S ~ o f S ~ a n d S ~ a n d t h e s y s t e m
o f r a t i o n a l i n t e g e r s s a t i s f y i n g
h k
1. 3 0 ~ zi j = -JS~' ~ O<zi~j E Z .i=I j=1 zij = ~i' --
W e n o t i c e t h a t
1 . 31 S ~ N ~ S ~ - I = x S < S ,i,j ij -
i f S z i j i s t h e s u b g r o u p o f t h e zi j! p e r m u t a t i o n s o f S f i x i n g
t h e e l e m e n t s o f G \ ( g ~ G ~ Q ~ ) , S : = { I ] ~ S .
T h e n u m b e r o f s u c h s y s t e m s [ zi j } w h i c h f u l f i l 1 . 3 0 i s o b v i o u s l y
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 24/197
19
e q u a l t o t h e c o e f f i c i e n t o f
: = X l " ' " ~ t ~ 1
in
h , k
i,~=I (1-xiYj)-1
oo
( x i , Y j i n d e p e n d e n t i n d e t e r m i n a t es ) ; f r o m w h i c h i t f o l l o w s t ha t :
The number of distinct• double c osets.. S~S~ of S and S~ in
S is equal to the coefficien t of x~y ~ in ~ (1-xiY~) -1.L
W e n o t i c e t h a t d u r i n g t h e s e g r o u p - t h e o r e t i c a l c o n s i d e r a t i o n s t h e
~ ( 1 - x i Y j ) -I m a k e t h e i r a p p ea r a nc e , w h i c h p l a y ano l y n o m i a l s
i m p o r t a n t r o l e i n t h e c h a r a c t e r t h e o r y o f t h e s y m m e t r i c g r o u p
a n d i n t h e t h e o r y o f t h e s o - c a l l e d S - f u n c t i o n s ( c f . L i t t l e w o o d
[2], 5.2, 6.4).
S p e c i a l d o ub l e c o s et s S ~ S ~ a r e t ho s e c o r r e s p o nd i n g to s o l u t io n s
[ zi j o f 1 . 3 0 w h i c h s a t i s f y O ~ z i j~ 1 , i . e . ( c f . 1 .3 1 )
fl ~ S ~ -1 = [1].S
P o r t h e i r n u m b e r w e g e t f r o m 1 . 3 2:
T h e n u m b e r o f d o u b l e c o s e t s S a ~ S ~ w i t h t he p r o p e r t y
S N ~ S ~ -1 = [1} is equal to the coeff icient of xay ~ in
7 T ( 1 + x i y -
O o n c l u d i n g t h i s s e c t i o n w e c o n s i d e r c e r t a i n p a i rs ( u , ~ ) o f p a r -
t i t i o n s w i t h r e s p e c t t o t h i s n u m b e r o f c e r t a i n d o u b l e c o s e t s .
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 25/197
2 0
A p a r t i t i o n 5 = ( 5 1 , . . . , ~ h ) o f n c an b e i l l u s t r a t e d b y a Y o u n g -
d i a g r a m [ 5 ] c o n s i s t i n g o f n n o d e s i n h r o w s , w i t h 5 n o d e s i n t h e
i - t h r o w a n d a l l t h e h r o w s s t a r t i n g i n t he s a m e c o l u m n . E . g . t h e
p a r t i t i o n ( 3 , 2 , 1 , 1) = : ( 3 , 2 , 1 2 ) c a n b e i l l u s t r a t e d b y
[ 3 , 2 , 1 2 ] : •
O n a c c o u n t o f t h e c o n d i t i o n ~ j ~ a j + I (l ~j <_ n- 1) i t m a k e s s e n s e t o
s p e a k o f c o l u m n s o f th e d i a g r a m [ a ] , a n d o f t h e l e n g t h ~ o f t h e
i - t h c ol u m n . H e n c e t o t h e p a r t i t i o n ~ t h e r e c o r r e s p o n d s t h e
p a r t i t i o n
1 . 3 4 ' := ~) 1a' := ( ~ , . . . , ~ , = a l ) , ~ i j : ~ > i
~' i s c a l l e d t h e a s s o c i a t e d p a r t i t i o n o f ~, [ ~' ] t he Y o u n g -
d i a g r a m a s s o c i a t e d w i t h [ ~ ] w h i c h a r i s e s b y i n t e r c h a n g i n g t h e
r o w s a n d c o l u m n s , e . g .
[ 3 , 2 , 1 2 ' ] = [ 4 , 2 , 1 ] :
@
P a r t i t i o n s ~ a n d Y o u n g - d i a g r a m s [ 5] w i t h t h e p r o p e r t y ~ = ~ '
r e s p . [ 5] = [ 5' ] a r e c a l l e d s e l f a s s o c i a t e d , a n d i t w i l l a p p e a r
i n s e c t i o n 4 , t h at t h e f o l l o w i n g l e m m a i s c r uc i a l :
1 . 3 5 Y o u n g - s u b g r o u p s S ~ a n d S a , p o s s e s s e x a c t l y o n e d o u b l e c o s e t
$ 5 ~ S ~ , w i t h t h e p r o p e r t y t h a t S ~ 0 ~ S ~ , ~ - 1 = { 1 ].
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 26/197
21
P r o o f : W e w a n t t o u s e 1 . 3 3 a n d h e n c e w e p r o v e b y i n d u c t i o n w i t h
r e s p e c t t o h , t h a t
c o e f f , o f x ~ y ~ ' i n ( l + x i Y j ) ] = I .i , ~ = I
( i) h = 1 : O b v i o u s l y
[ c o e f f . o f x I ~ Y i i n j ~l = ( 1 + x l Y j ) ~ = I .
( i i ) I f w e a s s u m e t h a t ~ h = r , t he i n d u c t i o n h y p o t h e s i s i s
h -1 ~ i ~ - I ~ '- I ~' ~ , h - ~ h '
i~_ r r+l in .TT. +x iy j ]=1coeff. of ( = xi )Yl "''Yr Yr+l "''Yh' i,j
r
M u l t i p l y i n g b o t h s i d e s w i t h J~1= x h y j g i v e s
h ~ h ' ) ~ i xh Y~ c o e f f . o f x ~ y ~ ' i n i , j - 1 ( 1 + x i Y j = J ) = I .
~wS i n c e ~ h = r t h e c o e f f i c i e n t o f x ~ y i s t h e s a m e i n
h ~ h ' ri,~=I (l+x iYj) j~=lXhYj
a s i ~
( + x i Y j ( x h Y ji,J-1 =
a s w e l l a s ( s i n c e a ~ < _ h- 1 f o r j > r) i n
h ~ ' h '= g I
i,'J~l ~ ~ j=l ~ ~ i~J ~l
T h i s t o g e t h e r w i t h 1 . 3 3 y i e l d s t h e s t a t e m e n t.
q . e . d .
T h e d o u b l e c o s e t 8 ~ 8 ¢ , w i t h S ¢ n ~ S ¢ , ~ - I = [ 1 ] m a y b e i l l u s t r a -
t e d b y a s o- c a l l ed Y o u n g - t a b l e a u w h i c h a r i s e s fr o m t he Y o u n g - d i a -
g r a m [ a] b y r e p l a c i n g t h e n o d e s b y t h e s y m b o l s 1 , . . . , n o f G . E . g .
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 27/197
22
3 5 1
4 6
2
7
i s a t a b l e a u w i t h d i a g r a m [ 3 , 2 , 1 2] .
a a t
If gi' gJ are the sets of symbol s in the i-th row, j-th col,lmn
o f t h e t a b l e a u T a , t h e e l e m e n t s o f t h e Y o u n g s u b g r o u p s S = x S a i
r e s p . S ¢ , : X S ~ ( S ~ i r e s p . S a ~ f i x i n g t h e e l e m e n t s o f . \ ~
r e s p. ~ \ Q ) a r e c a l le d h o r i z o n t a l p e r m u t a } i o n s r e s p. v e r t i c a l
per mut @ti ons of T a. The gr oups o_~f ll the hori zon tal resp. all t he
ver tic al permutatlions of T a are indic ated by
H ~ resp. V a .. 36
T h e y s a t i s f y
1.37~ n v ~ = {I} .
T h e r e f o r e t h e t a b l e a u T i l l u s t r a t e s t h e d o u b l e c o s e t S a l S a ,
wi th S O ~Sa,~-1 = [I] in the fol low ing sense: If S := H u
a n d i f w e a r e g i v e n S a , ~ S n, t h e n T m i l l u s t r a t e s p e r m u t a t i o n s
p ( n a m e l y t h e p w i t h p S a , p - I = V a ) w h i c h s a t i s f y S ~ N p S ~ , p - 1 = [ S } .
T h e s e a r e t h e r e s u l t s o n s y m m e t r i c a n d a l t e r n a t i n g g r o u p s w e
w i s h e d t o s u m m a r i z e f i r s t .
P r o m n o w o n w e s h a l l u s e t h e c i t e d r e s u l t s o n t h e s y m m e t r i c g r o u p
a n d i t s c o n j u g a c y c l a s s e s t o d e f i n e a n d e x a m i n e w r e a t h p r o d u c t s .
W e s h a l l r e t u r n i n s e c t i o n 4 t o d o u b l e c o s e t s t o c o n s t r u c t i d e m -
p o t e n t e l e m e n t s o f t h e g r o u p a l g e b r a of S w h i c h g e n e r a t e m i n i m a l
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 28/197
23
l e f t i d e a l s a f f o r d i n g i r r e d u c i b l e r e p r e s e n t a t i o n s o f S o v e r t h e
f i e l d o f c o m p l e x n u m b e r s .
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 29/197
2 4
2. W r e a t h p r o d u c t s
W e d e f i n e t h e w r e a t h p r o d u c t o f t w o g r o u p s a s f o l l o w s ( s e e e. g .
H u p p e r t [ I] , I § 1 5 ) :
I f G i s a g r o u p , H a p e r m u t a t i o n g r o u p o n t h e s e t o f
s y m b o l s ~ = { S , . . . , n ] , t h e s e t
{ ( f ; ~ ) I f m a p p i n g ~ i n t o G , ~ 6 H }
t o g e t h e r w i t h t h e c o m p o s i t i o n l a w
( f ; ~ )( f , ; ~, ) : = c ~ f , , ~ , )
i s c a l l e d t h e w r e a t h p r o d u c t G ~ H o f G w i t h H ( s o m e -
t i m e s G - w r e a t h w i t h H ) .
I n c l u d e d t h a t t o f : G ~ G a n d ~ E H t h e m a p p i n g f ~ : g - G i s d e -
f i n e d b y
f ( ~ ( i ) ) := f C i ) , V i ~ ~ ,
a n d f o r t w o m a p p i n g s f , f ' : G ~ G t h e i r p r o d u c t f f ' : ~ - G b y
f f ' ( i ) : = f ( i ) f ' ( i ) , V i ~ ~ ,
G ~ H i s a g r o u p a s c a n b e s e e n e a s i l y . W h i l e c h e c k i n g t h i s o n e
n o t i c e s , t h a t
2 . 2 ( f ) ~ , = ~ , ~ , V f , ~ , ~' ,
s i n c e p r o d u c t s o f p e r m u t a t i o n s h a v e t o b e r e a d he r e f r o m r i g h t
t o l e f t .
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 30/197
2 5
I f w e d e no t e b y e : ~ ~ G t h e m a p p i n g w i t h t h e v a l u e s
e(i ) = 1 , v i E ~,
a n d i f w e d e f i n e t o f : Q ~ G t h e m a p p i n g f - l : ~ ~ G b y
f - 1 ( i ) : = f ( i ) - I , V i E Q ,
w e h a v e f o r t h e i d e n t i t y e l e m e n t o f G ~ a n d f o r t he i n v e r s e o f
( f ; ~ ) :
2 . 3 1 G ~ = ( e ; 1 H ) , ( f ; ~ ) - I = ( f - 1 1 ; ~ - 1 ) _
( ( f ~ _ 1 ) - 1 = ( f - 1 ) ~ _ 1 = : f -1 _1 "
T h e o r d e r o f t h i s g r o u p i s
2.4 I Q ~ I = l a i n l ~ l .
E o r t h e d e r i v a t i o n o f t h e r e p r e s e n t a t i o n t h e o r y o f t h e s e g r o u p s
w h i c h w e a r e i n t e r e s t e d i n , t h e f o l l o w i n g n o r m a l d i v i s o r i s v e r y
i m p o r t a n t =
2 . 5 G * : = [ ( f ; 1 H ) ] f : Q ~ G ] = G1 X . . . x Gn ~ G~ H .
G * i s c a l l e d t h e b a s i s g r o u p o f G ~ . I t i s t h e d i r e c t p r o d u c t o f
n c o p i e s G i o f G :
2 . 6 G i : = ( ( f ; 1 H ) I f( J) = 1 , V j + i] ~ G .
T h e s u b g r o u p
2 . 7 H ' : = [ ( e ; ~ ) I ~ E H I ~ H
i s th e c o m p l e m e n t o f G * a n d i s o m o r p h i c t o H , i . e .
2 . 8 G ~ = G * H ' , G * ~ G ~ , G * N H ' = I G ~ = ( e ;1 H ) •
L e t u s n o w l o o k f o r e x a mp l e s . W e s h a l l r e c o g n i z e s o m e s u b g r o u p s
o f t h e s y m m e t r i c g r o u p a s p e r m u t a t i o n r e p r e s e n t a t i o n s o f c e r -
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 31/197
26
t a i n w r e a t h p r o d u c ts . L o o k i n g f o r t h e s e e x a m p l es w e m a y f o l l o w
t h e h i s t o r i c a l d e v e l o p m e n t o f t h e s e i de a s .
S u c h p e r m u t a t i o n g r o u p s a r o s e i n t h e p r o c e s s o f c o n s t r u c t i n g a
p - S y l o w - s u b g r o u p o f t h e s y m m e t r i c g r o u p , e v e n b e f o r e S y l o w
p r o v e d h i s f a m o u s t h e o r e m s i n 1 87 2 .
T h e f i r s t d e s c r i p t i o n o f t h i s c o n s t r u c t i o n w a s p r o b a b l y g i v e n b y
A . 0 a u c h y i n t h e t h i r d v o l u m e o f h i s " E x e r c i s e s d ' a n a l y s e e t d e
p h y s i q u e m a t h ~ m a t i q u e " w h i c h a p p e a r e d i n 1 8 4 4 ( cf . a l s o t h e
s e c t i o n s 3 9 a n d 4 0 o f E . N e t t o ' s " S u b s t i t u t i o n e n t h e o r i e u m d i h r e
A n w e n d u n g e n a u f d i e A l g e b r a " ( 1 88 2 ) a s w e l l a s A . R a d z i g ' s d i s -
s e r t a t i o n " D ie A n w e n d u n g d e s S y l o w ' s c h e n S a t z e s a u f d i e s y m m e t -
r i s c h e u n d d i e a l t e r n i r e n d e G r u p p e " ( 1 8 9 5 )) .
L e t u s d e n o t e b y e p ( m) t h e e x p o n e n t o f t h e m a x i m a l p o w e r o f a
p r i m e n u m b e r p d i v i d i n g m . I f w e a s s u m e t h a t p S ~ n , p S + S ) n a n d
a s p S < n ( O < a s <P ) , b u t ( a s + 1 ) p S > n , t h e n s i n c e
n! = 1 . 2 ' . . . . p S ( p S + 1 ) . . . 2 p S . . . a s p S ( a s p S + 1 ) ' ' ' ( a s p S + ( n - a s p s) )
w e c a n c o n c l u d e t h a t
e p ( n ! ) = a s e p ( p S ! ) + e p ( ( n - a s p S ) ! ) .
n o w a s _ I p s - 1 < n - a ss , _ ( a s _ 1 + 1 ) p S - 1 > n - a s p s, t h e n i n t h e s a m e w a yf
ep(n~ ) • a s _ s e p ( p s -1ase p(p s,) + !)
a n d s o o n.
H e n c e t h e p r o b l e m o f c o n s t r u c t i n g a p - S y l o w - s u b g r o u p o f S c a n
b e r e d u c e d t o t h e c o n s t r u c t i o n o f a p - S y l o w - s u b g r o u p o f s y m -
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 32/197
27
m e t r i c g r o u p s S p r of p - p o w e r - d e g r e e s p r.
T h e m a x i m a l p o w e r o f p i n p r , i se p ( p r : p 1 + p + p 2 + . . . + p r -1 p ( 1 + p + . . . + p r - 2 ) p P
p ---- _--
2.9 ep(p -1 !)P
= p P ,
h e n c e e v e r y p - S y l o w - s u b g r o u p p r o f S r h a s t h e o r d e r
P
2 . 1 0 I r l = I p r - l l p p ,
i f p r - 1 i s a p - S y l o w - s u b g r o u p o f 8
pr-1"
T h e r e f o r e i t w o u l d b e d e s i r a b l e t o c o n s t r u c t w i t h t h e a i d o f
p r - 1 _ w h i c h i s a p e r m u t a t i o n g r o u p o f d e g r e e p r- 1 _ a p e r m u t a -
tion group of degree pr and of order I r-11 p P. On accou nt of
2 . 1 0 t h e r e s u l t w o u l d b e a p - S y l o w - s u b g r o u p o f S p r .
T h a t t h i s m i g h t b e d o n e b y c o n s t r u c t i n g a f ai t h f u l p e r m u t a t i o n
r e p r e s e n t a t i o n o f p r - 1 ~ C p ( C p : = < ( 1 . . . p ) > _ ( S p ) i s s u g g e s t e d b y
a c o m p a r i s o n o f 2 . 4 a n d 2 . 1 0 .
M o r e g e n e r a l l y : f r o m t w o p e r m u t a t i o n g r o u p s G an d H o f th e d e -
g r e e s m a n d n c o n s t r u c t a p e r m u t a t i o n g r o u p o f d e g r e e m n a n d o f
t h e o r d e r I G I n lH I .
W e p r o v e f i r s t :
2.11 If
G
i s a p e r m u t a t i o n r e p r e s e n t a t i o n o f G o n t h e s et o f s y m b o l s
r = { 1 , . . . , m } t h e n
( f ; ~ ) ( i , j ) : = ( f ( ~ ( j ) ) ( i ) , ~ ( j ) ) , V ( i ,j ) E 2 × 9 ,
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 33/197
2 8
y i e l d s a p e r m u t a t i o n r e p r e s e n t a t i o n o f G ~ H o n Fx~ .
T h i s p e r m u t a t i o n r e p r e s e n t a t i o n o f G ~ H is f a i t h f u l i f t h e
p e r m u t a t i o n r e p r e s e n t a t i o n o f G i s f a i t h f u l , a n d i t i s t r a n -
s i t i v e i f b o t h G ( o n F ) a n d H ( o n G ) a r e t r a n s i t i v e .
P r o o f : a ) I t i s e a s y t o v e r i f y , t h a t
C f ; ~ ) C C f ' ; ~ ' ) C i , j ) ) = C f f ~ ; ~ ' ) C i , j ) , v f , f ' , ~ , ~ ' , i , j .
A n d f r o m
C f ; ~ ) C i , j ) = C f ; ~ ) C i ' , j ' )
w e g e t
( f C ~ C j ) ) C i ) , ~ C J ) ) = C f C ~ C j ' ) ) C i ' ) , ~ C j ' ) ) •
i s a p e r m u t a t i o n , h e n c e t h i s i m p l i e s j = j' , s o t h a t w e h a v e
f C ~ ( j ) ) ( i ) = f C ~ C j ) ) ( i ' ) °
f C ~ ( j ) ) i s a p e r m u t a t i o n , t o o , h e n c e i = i ' .
T h u s w e h a v e o b t a i n e d a p e r m u t a t i o n r e p r e s e n t a t i o n o f G ~ H a s
c l a i m e d .
b ) I f ( f ; ~ ) i s i n t h e k e r n e l w e h a v e
C i , j) = ( f ; ~ ) C i , J ) = ( f C ~ C j ) ) C i ) , ~ ( j ) ) , v i , j .
I f t h e g i v e n p e r m u t a t i o n r e p r e s e n t a t i o n o f G i s f a i t h f u l t h i s
i m p l i e s f ( j ) = IG , V j , a n d h e n c e i n t h i s c a s e f = e , s o t h a t
t h e r e p r e s e n t a t i o n o f G ~ H i s f a i t h f u l , t o o .
c ) F i n a l l y i f G is t r a n s i t i v e o n F , H t r a n s i t i v e o n ~ , a n d ( i , j )
a n d ( i ' , j ' ) a r e t w o s y m b o l s o u t o f Fx G , t h e r e i s a ~ E H a n d a
g E G su ch t hat ~(j) = j' and g (i) = i'.
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 34/197
2 9
I f w e c h o o s e a n f : g - G s o t h a t f ( j ' ) = g , t h e n
( f ; ~ ) ( i , j ) = ( f ( ~ ( j ) ) ( i ) , ~ ( j ) ) = ( f ( j ' ) ( i ) , j ' ) = ( i ' , j ' ) ,
a n d t h e p e r m u t a t i o n r e p r e s e n t a t i o n o f G % H i s t r a n s i t i v e a s w e l l .
T h i s c o m p l e t e s t h e p r o o f .
q . e . d .
T h e p e r m u t a t i o n r e p r e s e n t a t i o n o f G ~ H g i v e n in 2 . 11 i s o f d e g r e e
I rx ~J = mn . T w o p e r m u t a t i o n g r o u p s G I a n d G 2 o n G 1 a n d ~ 2 a r e
c a l l e d s i m i l a r , i f t h e r e i s a b i J e c t i v e m a p p i n g ~ o f G I o n t o ~ 2
a n d a n i s o m o r p h i s m ~ o f G I o n t o G 2 s o t h a t
2 . 1 2 E ( g ( i ) ) = ~ ( g ) ( e ( i ) ) , V i E g f, g E G 1 •
W e w o u l d l i k e t o d e s c r i b e a s u b g r o u p o f S m n s i m i l a r t o t h e p e r m u -
t a t i o n r e p r e s e n t a t i o n o f G ~ g i v e n b y 2 . 11 .
F o r s u c h a n E : F x ~ ~ A = { 1 , . . . , m n ] w e c h o o s e t h e b i j e c t i o n d e -
f i n e d b y
2 . 1 3 E ( i , j ) : = ( j - 1 ) m + i , 1 ~ i ~ m , l ~ j ~ n .
T o d e s c r i b e a n i s o m o r p h i s m o f t h e p e r m u t a t i o n r e p r e s e n t a t i o n o f
G ~ H i n t o S mn w e f i r s t d i v i d e t h e s e t A o f t h e s y m b o l s o n w h i c h
S m n a c t s i n t o n p a i r w i s e d i s j o i n t s u b s e t s A i of o r d e r m , s a y
2 . 1 4 A = { 1 , . . . , m , m + 1 , . . . , 2 m , . . . , ~ n - 1 ) m + l , . . . , n ~ } •
A 1 A 2 ... A
N o w l e t e b e a p e r m u t a t i o n w h i c h p e r m u t e s t h e A i c y c l i c a l l y , s a y
2 . 1 5 a := ( 1 , m + 1 , . . . , ( n - 1 ) m + 1 ) ( 2 , m + 2 , . . . ) . . . ( m , 2 m , . . . , n m ) .
W i t h t h e a i d o f a w e n o w d e f i n e a n i s o m o r p h i s m ~ o f t h e p e r m u -
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 35/197
3 O
r a t i o n r e p r e s e n t a t i o n o f G ~ H i n t o S m n a s f o l l o w s . W e d e f i n e f i r s t
t h e i m a g e s o f t h e v a l u e s f ( i ) o f f b y
2 . 1 6 ~ ( f ( i ) ) : = a i - l f ( i ) a I - i = : ~ i '
s o t h a t ~ i a c t s o n A i , a n d
2 . 1 7 ~ ( f ; 1 H ) : = ~ i ~ i •
N o w l e t
2 . 1 8 ~ ( e ; ~ ) = : ~ *
b e d e f i n e d a s f o l l o w s :
2 . 1 9 ~ * ( ( j - 1 ) m + i ) : = ( ~ ( j ) - 1 ) m + i , 1 ~ i <_ m , 1 ~ j ~ n ,
s o t h a t
2 . 2 0 ~ * A i = A ~ ( i ) "
T h i s m e a n s , t h a t t h e i m a g e o f ( e ;~ ) u n d e r ~ i s t h e p e r m u t a t i o n
o f t h e A c o r r e s p o n d i n g t o t h e p e r m u t a t i o n ~ o f t h e s y m b o l s i
o f ~ = [ 1 , . . . , n ) . A s c a n e a s i l y b e s e e n , t h i s m a p p i n g @ d e f i n e d
b y
2 . 21 ~ ( f ; ~ ) : = ~ l . . . ~ n ~ *
i s a n i s o m o r p h i s m o f t h e p e r m u t a t i o n r e p r e s e n t a t i o n o f G ~ H
d e s c r i b e d i n 2 . 11 i n t o Sm n . T h e i m a g e o f t h e p e r m u t a t i o n r e p r e -
s e n t a t i o n i s o b v i o u s l y
2 . 2 2 ( G I x . . . x G n ) H ' ~ S m n ,
w i t h G I e q u a l t o t h e p e r m u t a t i o n r e p r e s e n t a t i o n o f G an d
2 . 2 3 G i = ~ i - l G l a l - i •
H ' i s t h e p e r m u t a t i o n g r o u p a c t i n g o n t h e s u b s e t s A i o f A a s H
a c t s o n t h e s y m b o l s i o f ~ ; H ' i s a s u b g r o u p o f th e s u b g r o u p
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 36/197
31
S'n - S m n w h i c h c o n s i s t s o f t h e n'. p e r m u t a t i o n s o f t h e A .
T o p r o v e t h e s i m i l a r i t y w e h a v e t o v e r i f y , t h a t 2 . 1 2 i s v a l i d .
S t a r t i n g w i t h t h e l e f t h a n d s i d e o f 2 . 1 2 w e o b t a i n
¢ ( ( f | ~ ) ( i , j ) ) = ¢ ( f ( ~ ( j ) ) ( i ) , ~ ( j ) ) = ( ~ ( j ) - 1 ) m + f ( ~ ( j ) ) ( i ) .
A n d o n t h e r i g h t h a n d s i d e w e h a v e
@ ( f | ~ ) ( ~ ( i , j ) ) -- ~ l . . . ~ n ~ * ( ( J - 1 ) m + i)
= ~ l . . . ~ n C ( ~ ( j ) - l ) m + i) = ( ~ ( J ) - l ) m + f ( ~ ( j ) ) ( i ) .
T h u s w e h a v e p r o v e d t h e f o l l o w i n g :
2 . 2 5 T h e m a p p i n g s E a n d ~ d e f i n e d b y 2 . 1 3 - 2 . 2 1 m a p t h e p e r m u t a t i o n
r e p r e s e n t a t i o n o f G ~ H d e s c r i b e d b y 2 .1 1 o n t o a s i m i l a r s u b -
g r o u p o f S m n .
I t i s i n t e r e s t i n g t o se e , t h a t t h e s e g r o u p s a r e t h e p e r m u t a t i o n
g r o u p s u s e d b y C a u c h y a n d N e t t o t o c o n st r u c t S y l o w - s u b g r o u p s o f
t h e s y m m e t r i c g r o u p a n d w h i c h a r o s e a t t h e b e g i n n i n g o f th e d e -
v e l o p m e n t o f t h e c o n c e p t o f t h e w r e a t h p r o d u c t o f g r o u p s . A
s k e t c h o f t h i s c o n s t r u c t i o n r e a d s a s f o l l o w s :
2 ~ A f a i t h f u l p e r m u t a t i o n r e p r e s e n t a t i o n o f d e g r e e m u o f t h e
w r e a t h p r o d u c t o f t w o p e r m u t a t i o n g r o u p s G ( o n F = ~ 1 , . . . , m ~ )
a n d H ( o n G = ( 1 , . . . , n ) ) c a n b e o b t a i n e d a s f o l l o w s :
D i v i d e t h e s e t A = ~ 1 , . . . , m n ~ o n w h i c h S t u n a c t s i n t o d i s -_..
j o i n t s u b s e t s A I = F , A 2 , . . ., A o f o r d e r m. ~ o r m t h e d i r e c t
p r o d u c t o f G = G I ( o n A t = F ) w i t h t h e s u b g r o u p s G i ( o n t h e
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 37/197
32
s u b s e t s A i ) w h i c h c o r r e s p o n d t o G 1 ( 2_ (i _( n) a n d m u l t i p l y
G I x . . . x G w i t h t h e s u b g r o u p H ' c o r r e s p o n d i n g t o H a n d
a c t i n g o n t h e s u b s e t s A i a s H a c t s o n t h e s y m b o l s i o f 9.
T h e r e s u l t
( G I x . . . X G n ) g '
i s t h e d e s i r e d f a i t h f u l p e r m u t a t i o n r e p r e s e n t a t i o n o f G ~ H
a n d i t i s t r a n s i t i v e i f b o t h G ( o n F ) a n d H ( o n 9 ) a r e
t r a n s i t i v e .
A s i m p l e e x a m p l e i s t h e r e p r e s e n t a t i o n o f S 2 % S 2 = C 2 % C 2 ( i f w e
d e n o t e b y C t h e c y c l i c g r o u p of o r d e r n ):
C2%02 = { ( 1 , 1 ; 1 ) , ( 1 , ( 1 2 ) ; 1 ) , ( ( 1 2 ) , 1 ; 1 ) , ( ( 1 2 ) , ( 1 2 ) ; 1 ) , ( 1 , 1 ; ( 1 2 ) ) ,
( 1 , ( 1 2 ) ; ( 1 2 ) ) , ( ( 1 2 ) , 1 ; ( 1 2 ) ) , ( ( 1 2 ) , ( 1 2 ) ; ( 1 2 ) ) 3
( ( f ;~ ) w r i t t e n i n t h e e x p l i c i t f o r m ( f ( 1 ) , f ( 2 ) ; ~ ) ) i s s i m i l a r t o
( [ 1 , ( 1 2 ) ] X { 1 , ( 3 4 ) ] ) [ 1 , ( 1 3 ) ( 2 4 ) ]
= { 1 , ( 1 2 ) , ( 3 # ) , ( 1 2 ) ( 3 ¢ ) , ( 1 3 ) ( 2 4 ) , ( 1 ¢ ) ( 2 3 ) , ( 1 3 2 4 ) , ( 1 4 2 3 ) 3 .
T h i s i m a g e o f C 2 % 0 2 i s a 2 - S y l o w - s u b g r o u p o f S 4 .
C o m i n g b a c k t o t he p - S y l o w - s u b g r o u p s w e g e t f r o m t h e s e c o n s i d e r a -
t i o n s :
p r I o n F = { 1 .. pr-1. 2 6 I f p r - 1 i s a p - S y l o w - s u b g r o u p o f S _ , ., 3 ,
a n d i f C p = < ( 1 . . . p ) > < S p , t h e n t h e s u b g r o u p o f S r s i m i l a r
t o p r - 1 % C p a s d e s c r i b e d i n 2 . 2 5 i s a p - S y l o w - s u b g r o u p .
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 38/197
3 3
U s i n g t h i s r e s u l t w e c a n c o n s t r u c t a p - S y l o w - s u b g r o u p o f S .
I ft
n = ~ ai i , O_(ai<p,i = 0
t h e n as c a n b e s e e n f r o m c o n s i d e r a t i o n s a b o v e t h e e x p o n e n t o f
t h e m a x i m a l p o w e r o f p d i v i d i n g n ! i s
2 . 2 7
e p ( n !) = a I + a 2 ( 1 + p ) + . . . + a t ( 1 + p + . . . + p t - l )
= a l e p ( p ! ) + a 2 e p ( p 2 ! ) + . . . + a t e p ( p t ! ) •
L e t u s n o w d i v i d e t h e s e t G = [1 , . . . , n ] o n w h i c h S a c t s i n t o
p a i r w i s e d i s j o i n t s u b s e t s a s f ol l o w s . W e d i v i d e ~ i n t o t h e s u b -
s e t G o : = [ 1 ' ' ' ' ' a o ] o f o r d e r a o , i n t o t h e a I s u b s e t s ~ 11 : =
[ a o + 1 , . . . , a o + P ), . . . , ~ 1a I : = [ a o + ( a 1 - 1 ) p + 1 , . . . , a o + a l P 3 o f o r d e r
p , . . . , a t s u b s e t s ~ t 1 ' ' ' ' ' Q t a t o f o r d e r p t . O n e a c h o f t h e s e
" - o f . ( r e g a r d e d a su b s e t s ~ i J f o r m a p - S y l o w - s u b g r o u p p l I~ C p S p I
s u b g r o u p o f S n ) . A n d n o w t a k e t h e i r d i r e c t p r o d u c t
ta i
( p i - l ~ O p ) ) ~ Sx ( xi=I
a × . . . x p i - 1 ~ O p ( a ix ( p i - 1 ~O p ) : = p i - 1 ~ O p f a c t o r s ) ) .
e ~ ( n ! )
T h e r e s u l t i n g s u b g r o u p i s o f o r d e r p ~ a n d h e n c e a p , S y l o w -
s u b g r o u p o f S . T h u s w e h a v e d e r i v e d t h e w e l l - k n o w n c o n s t r u c t i o n
o f p - S y l o w - s u b g r o u p s f i r s t g i v e n b y C a u c h y ( f o r t h i s a n d o t h e r
r e s u l t s c o n c e r n i n g p - S y l o w - s u b g r o u p s o f s y m m e t r i c g r o u p s cf .
a l s o t h e p a p e r s o f L . K a l o u j n i n e a n d t h e p a p e r o f W e i r ( s e e t h e
r e f e r e n c e s ) ) :
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 39/197
3 4
2 , 2 8 I f n = Z a i p i ( O ~ a i < P) , t h e n e v e r y p - S y l o w - s u b g r o u p o f S
a i ( p i - 1 % C p ) )i s o f t h e f o r m × ( x
i
T h i s a s w e l l a s 2. 2 6 g i v e s a r e c u r s i o n f o r m u l a f o r t h e c o n s t r u c -
t i o n o f a p - S y l o w - s u b g r o u p . B e c a u s e o f t h e a s s o c i a t i v i t y o f t h e
w r e a t h p r o d u c t m u l t i p l i c a t i o n t h i s c an b e w r i t t e n e x p l i c i t l y:
2 . ~ L e t G , H an d I b e p e r m u t a t i o n g r o u p s o n F , G a n d A. T h e n
( G % H ) % I and G % ( H %I ) a r e c o r r e s p o n d i n g p e r m u t a t i o n g r o up s ,
i f w e i d e n t i f y ( F × G ) x A a n d F × ( ~ × A ) a c c o r d i n g t o
( ( i , j ) , ~ ) = C i , C J , ~ ) ) •
P r o o f : L e t ( f ;= ) b e a n e l e m e n t o f ( G x H ) % I s o t h a t f( i ) =
( f i ; ~ i ) E G % H , i E A . A n d l e t ( f * ; ~ * ) b e a n e l e m e n t o f G % ( H % I )
w i t h ~ * = ( f ' ; ~ ) E H ~ I s o t h a t f ' ( i ) = ~ i a n d f * ( i , j ) = f j ( i ) .
T h e n o n th e o n e h a n d
( f ~ ) ( C i , J ) , k ) = ( ( f c k ) ; ~ C ~ ) ) ( i , j ) , ~ ( ~ ) )
= ( C f ~ c ~ ) C ~ c ~ ) C J ) ) C i ) , ~ ( ~ ) ( j ) ) , ~ ( k ) ) •
A n d o n t h e o t h e r h a n d
C f * ; ~ * ) C i , C j , ~ ) ) = C f * C C f ' ; ~ ) C J , ~ ) ) C i ) , C f ' ; ~ ) C j , k ) )
= ( f * C f ' C ~ C k ) ) C J ) , ~ C ~ ) ) C i ) , C f ' ( ~ ( k ) ) ( J ) , ~ ( k ) ) )
= C f ~ c ~ ) C ~ c ~ ) C ~ ) ) C i ) , ( ~ C ~ ) C j ) , ~ ( ~ ) ) •
T h u s ( f I ~ ) a c t s a s ( f * ; ~ * ) i f w e i d e n t i f y t h e s y m b o l s a s d e s -
c r i b e d .
q . e . d .
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 40/197
35
A c o r o l l a r y i s
2 . 3 0 I f O p : = < ( 1 . . . p ) > ~ S p , t h e n e v e r y p - S y l o w - s u b g r o u p o f S r
i s s i m i l a r t o t h e w r e a t h p r o d u c t
r
0 p : = O p ~ . . . ~ 0 p ( r f a c t o r s ) .
E v e r y p - S y l o w - s u b g r o u p o f S ( n = Z a l P i , O ~ a i <P ) i s s i m i l a r
t o
a r
x(xi( Op))i
A s w e h a v e s e e n , S y l o w - s u b g r c u p s o f s y m m e t r i c g r o u p s a r e d i r e c t
p r o d u c t s o f w r e a t h p r o d u c t s . I n t h e i n t r o d u c t i o n w e c l a i m e d , t h a t
t h i s i s a l s o v a l i d f o r t h e c e n t r a l i z e r s o f e l e m e n t s i n S .
T o s h o w t h i s , w e s t a r t w i t h a s p e c i a l c a s e , n a m e l y t h e c e n t r a l i -
z e r o f t h e p e r m u t a t i o n
= ~ 1 . . . ~ n : = ( 1 . . . m ) ( m + 1 , . . . , 2 m ) . . . ( . . . n m ) E Stun •
T h e c e n t r a l i z e r ( ~) o f t h i s p e r m u t a t i o n i sC S I Im
2.51 °Smn(~) = (<~I >'" <~ n> )S ~ "
T h a t m e a n s ( x) i s t h e p r o d u c t o f t h e s u b g r o u p g e n e r a t e d b yC S I Im
t h e c y c l i c f a c t o r s ~ i o f ~ w i t h t h e s u b g r o u p S ~ o f t h e n! p e r m u -
t a t i o n s o f S m n W h i c h p e r m u t e t h e se t s of sy m b o l s i n t h e c y cl i c
f a c t o r s o f ~ a s t h e y s t a n d .
F o l l o w i n g t h e c o n s i d e r a t i o n s p r e c e e d i n g 2 . 2 4 a n d 2 . 25 w e s ee ,
t h a t t h i s s u b g r o u p i s a p e r m u t a t i o n r e p r e s e n t a t i o n o f C m ~ S n -
A n d a p p l y i n g t h i s t o t h e s u b s e t s o f c y c l i c f a c t o r s o f t h e s a m e
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 41/197
3 6
l e n g t h i n a g e n e r a l p e r m u t a t i o n w e h a v e :
2 . ~ I f ~ E S n i s.....f t y pe T ~ = ( a l , . . . , a n ) , t h e n t h e c e n t r a l i z e r
o f ~ i n S i s a f a i t h f u l p e r m u % a t i o n r e p r e s e n t a t i o n o f
x ( c i ~ S a i )i
( c i ~ s o : = [ I ] , c i : = < ( i . . . i ) > _ ( s ) .
( R e m a r k : P r o m t h i s w e c a n d e r i v e a t o n c e t h e r e s u l t 1 . 2 3 a b o u t
t h e s p l i t t i n g o f S n - c l a s s e s i n t o A n - C l a s s e s . ) A n a l o g o u s l y , w e
h a v e t h e f o l l o w i n g r e s u l t w h i c h w i l l b e o f u s e l a t e r on :
I f S m n i s t h e s y m m e t r i c g r o u p o n G = { 1 , . . . , m n } , t h e n t h e
n
n o r m a l i z e r N S m ( × S ) o f t h e s u b g r o u p
nX S : = S X . . . × S ( n f a c t o r s )
( i - t h f a c t o r S o n g i : = { ( i - 1 ) m + 1 , . . . , i m ] ) i s t h e f a i t h -................
f u l p e r m u t a t i o n r e p r e s e n t a t i o n o f S m ~ S n d e s c r i b e d i n 2 . 2 4
a n d 2 . 2 5 .
T h e s e t h r e e e x a m p l e s , t h e p - S y l o w - s u b g r o u p s , t h e c e n t r a l i z e r s
n
o f e l e m e n t s a n d t h e n o r m a l i z e r s o f s u b g r o u p s o f t h e f o r m x S
i n s y m m e t r i c g r o u p s s h o w , h o w u s e f u l t h i s c o n c e p t o f t h e w r e a t h
p r o d u c t i s. M o r e o v e r t h e y g i v e a h i n t a s t o h o w t h e r e p r e s e n t a -
t i o n t h e o r y o f w r e a t h p r o d u c t s m a y b e a p p l i e d t o t h e r e p r e s e n t a -
t i o n t h e o r y o f t h e s y m m e t r i c g r o u p .
T h e c e n t r a l i z e r s o f p - e l e m e n t s a s w e l l a s t h e p - S y l o w - s u b g r o u p s
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 42/197
37
o f th e c e n t r a l i z e r s o f p - r e g u l a r e l e m e n t s p l a y a n i m p o r t a n t r o l e
i n t h e p - m o d u l a r r e p r e s e n t a t i o n t h e o r y o f f i n i t e g r o u p s . O n t h e
o t h e r h a n d i t i s k n o w n , t h a t t h e s o - c a l l e d s y m m e t r i z e d o u t e r
p r o d u c t s o f t w o i r r e d u c i b l e r e p r e s e n t a t i o n s o f S a n d S a r e r e -
p r e s e n t a t i o n s o f S m n i n d u c e d b y c e r t a i n i r r e d u c i b l e r e p r e s e n t a -
n
t i o n s o f N S m ( x S m ) .
T h e o t h e r w a y r o u n d w e m a y a s k h o w t h e r e p r e s e n t a t i o n t h e o r y o f
t h e s y m m e t r i c g r o u p c a n b e a p p l i e d t o d e r i v e t h e r e p r e s e n t a t i o n
t h e o r y o f c e r t a i n w r e a t h p r o d u c t s .
A b o u t 1 9 3 0 A . Y o u n g a p p l i e d h i s m e t h o d s t o t he s o - c a l l e d h y p e r -
o c t a h e d r a l g r o u p s . I n o u r n o t a t i o n t h e s e a r e g r o u p s o f t h e f o r m
S 2 ~ S n , a n d t h e y a r i s e b y r e p r e s e n t i n g t h e e l e m e n t s o f S b y p e r -
m u t a t i o n m a t r i c e s a n d a l l o w i n g no t o n l y +I a s n o n v a n i s h i n g e n -
tries but also -I (cf. Yo ung [I]).
P o l l o w i n g a s u g g e s t i o n o f I . S c h u r , W . S p e c h t t h e n c o n s i d e r e d
i n h i s d i s s e r t a t i o n s u c h g r o u p s w h e r e n o t o n l y ~1 a r e a l l o w e d
a s n o n v a n i e h i n g e n t r i e s b u t e v e n t he e l e m e n t s o f a g r o u p G i f
t h e m a t r i x m u l t i p l i c a t i o n i s d e f i n e d a p p r o p r i a t e l y ( S p e c h t [ 11 ).
T h e s e g r o u p s a r e o b v i o u s l y o f t h e f o r m G ~ S n . I n a f o l l o w i n g
p a p e r ( S p e c h t [ 2~ ) h e c o n s i d e r e d t h e g e n e r a l c a s e G ~ H, H a
f i n i t e p e r m u t a t i o n g r o u p . H e s h o w e d t h a t e s p e c i a l l y t h e o r d i n a r y
r e p r e s e n t a t i o n t h e o r y o f w r e a t h p r o d u c t s o f t h e f o r m G ~ S n c a n b e
l a r g e l y d e r i v e d w i t h t h e a i d o f t h e r e p r e s e n t a t i o n t h e o r y o f S .
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 43/197
38
N e v e r t h e l e s s t h e a p p l i c a t i o n o f t h e t h e o r y o f t h e r e p r e s e n t a t i o n s
o f w r e a t h p r o d u c t s t o t he r e p r e s e n t a t i o n t h e o r y o f t h e s y m m e t r i c
g r o u p i s n o t a v i c i o u s c i r c le . F o r t h o s e w r e a t h p r o d u c t s G ~ S
w h o s e r e p r e s e n t a t i o n s w e s h a l l a p p l y t o S s a t i s f y m < n , s o t h a t
o n t h e c o n t r a r y t h i s a p p l i c a t i o n p r o v i d e s a n i n t e r e s t i n g r e c u r s i o n
p r o c e s s .
I n o r d e r t o d e ri v e t h e r e p r e s e n t a t i o n t h e o r y o f w r e a t h p r o d u c t s o f
t h e f o r m G ~ n i t i s n e c e s s a r y t o e x a m i n e s u c h g r o u p s m o r e c l o s e l y.
T h i s w e s h a l l d o i n t h e f o l l o w i n g s e c t i o n .
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 44/197
3 9
3 . W r e a t h s w i t h s y m m e t r i c g r o u p s
W e s h a l l n o w c o n s i d e r w r e a t h p r o d u c t s o f th e f o r m G~ S n, - w r e a t h s
w i t h s ~, -e tr ic ~ . F o r t he t im e b e in g l et G d en ot e a f in it e
g r o u p .
S i n c e @ ~ S n m a y a r i s e a s d e s c r i b e d a t t h e e n d o f t h e l a s t s e c t i o n
b y i n s e r t i n g e l e m e n t s o f G f o r th e n o n v a n i s h i n g e n t r i e s o f p e r m u -
t a t i o n m a t r i c e s r e p r e s e n t i n g t h e e l e m e n t s o f Sn , t h e g r o u p G ~ S n
i s s o m e t i m e s c a l l e d t h e c o m p l e t e m o n o m i a l g r o u p ( o f d e g r e e n ) o f
G. O. Ore call ed it symm etr y (of degree n) of G (Ore [I]).
W r e a t h s O m ~ S n o f c y c l i c g r o u p s w i t h s y m m e t r i c g r o u p s h a v e b e e n
call ed ~ ene ral ize d s~,~,-etric grou ps by M. O sim a (Osima [I]), and
a n a l o g o u s l y t h e g r o u p s C m ~ A w e r e c a l le d g e n e r a l i z e d a l t e r n a t i n g
g r o u p s ( P u t t a s w a m a i a h [ I ]) . A s h a s b e e n m e n t i o n e d a b o v e , t h e
s p e c i al c as e 0 2 ~S i s c a l le d a h y p e r o c t a h e d ra l ~ .
L e t u s f i r s t c o n s i d e r t h e c o n J u g a c y c l a s s e s o f G ~ S n , w h i c h h a v e
b e e n c h a r a c t e r i z e d b y W. S p e c h t ( S p e c h t [ 1] ).
S i n c e [ I ~ S n ~ S t h i s c h a r a c t e r i z a t i o n p r o v i d e s a g e n e r a l i z a t i o n
o f t he c h a r a c t e r i z a t i o n o f t he c o n J u g a c y c l a s s e s o f s y m m e t r i c
g r o u p s b y t h e i r c y c l e d e c o m p o s i ti o n . W e c h o o s e t h e n o t a t i o n s o
t h a t w e s h a l l a b t a i n a g e n e r a l i z a t i o n o f t h e c h a r a c t e r i z a t i o n b y
t h e t y p e o f t h e p e r m u t a t i o n .
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 45/197
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 46/197
41
I n t h e s p e c i a l c a s e s = 1 , i . e . i n c a s e ~ I ] ~ S n = Sn , w e h a v e t h e
r o w ( a l , . . . a n ) a n d h e n c e 3 . 2 i s a g e n e r a l i z a t i o n o f t he d e f i n i t i o n
1 . 1 6 o f t h e t y p e o f a p e r m u t a t i o n .
W e w o u l d l i k e t o s h o w t h a t a s i n 1 . 1 4 / 1 . 1 6 , t w o e l e m e n t s o f
G ~ S n b e l o n g t o t h e s a m e c o n j u g a c y c l a s s i f a nd o n l y i f t h e y a r e
o f t h e s a m e t y p e .
B e f o r e w e c a n p r o v e t h i s w e n e e d s o m e p r e l i m i n a r y c o n s i d e r a t i o n s .
A t f i r s t w e n o t i c e , t h a t t h e e n t r i e s a i k o f t h e t y p e ( a i k ) o f a n
e l e m e n t ( f ;~ ) E G ~ S n , w i t h ~ o f t y p e ( a l , . . . , a n ) , s a t i s f y t h e
f o l l o w i n g e q u a t i o n s:
3 . 3 0 ( a i k E ~ , E a i k = a , Z k a i k = n .-- i i , k
T o e a c h ( s x n ) - m a t r i x ( a ik ) w h o s e e n t r i e s s a t i s f y 3 .3 , t h e r e a r e
e l e m e n t s i n G ~ S n , w h i c h a r e o f t h i s t y pe , s i n c e f r a n g e s o v e r a l l
t h e m a p p i n g s o f g in t o G.
S i n c e w e ar e m e r e l y i n t e r e s t e d i n t h e t y pe , w e n e e d o n l y d e t e r -
m i n e a c y c l e p r o d u c t u p t o c o n j u g a t i o n i n G . T h e r e f o r e w e s h o w
f i r s t , t h a t t h e c o n v e n t i o n t h a t t h e s y m b o l j i n 3. 1 i s t h e l e a s t
s y m b o l o f th e c o n s i d e r e d c y c l e i s u m n e c e s s a r y , i .e . t h a t
f . . . f r C J ) ~ f . . .f r C S C j )) , v s • .
P r o o f : W e c a n a s s u m e O ~ s( _ r. T h e n
f . . .f r ( ~S ( j) ) = f ( s ( j ) ) . . . f ( ~ ( j ) ) f ( j ) . . . f ( ~ s + 1 ( j ) ) . (I)
I f
a := f ( s ( j ) ) . . . f ( ~ ( j ) ) , b := f ( j) f ( - 1 ( j ) ) . . . f ( s + 1 ( j ) ) ,
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 47/197
4 2
then ab is the right hand side of the equation (1) , and ba is the
cyclepro duct to (j ... r(~)) wi th respec t to f (cf . 3.1). But
ab - ha: a-lab a = ha.
q.e.d.
respect to f,ff~-l.
Using 3.4 we obtain
g ' ~ f ~ , ( f ~ , ) ~, ~, -l "' '( f~ ')~, r ,-1(~'(J))
= f ~ , f ~ , ~ . . . f r C ~ ' C J ) ) = g .
And for g" we have
g, = f,ff, -lf,f f,T1...f, f f,-I (j)
A n o t h e r u s e f u l r e m a r k i s
3 . 5 T ( f ~ ) = T ( e; ~ ' ) (f ; ~ ) (e ; ~ ' ) -I
= ~ ( f , ; 1 ) C f ~ ) C f , ~ l ) - 1 ' Y f , f ' , ~ , ~ ' .
Proof: We have
( e ; ~ , ) ( f ; ~ ) ( e ; ~ , ) - I = ( f , ; ~ , ~ , - 1 ) ,
(fVll)(f;~)(f,;1)-1 = (fvff~-l|~).
Henc e it suffices to prove, th at the right hand sides of these
two equations are elements of type T(f;~).
To decide this, it suffices to show, that the cycle produc t g to
the cyclic factor (j...~r(j)) of ~ with r espect to f is conjugate
to the follow ing two cycleproducts: the cycleproduct g' belon ging
to the cyclic factor (~,(j)...~,~r(j)) of ~, ~, -I with respect to
f~, and the cyclepro duct g" associated wit h (j ... r(j)) wit h
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 48/197
43
= z , t ~ j g f , ~~ ' - ' - - " ~ g •
q . e . d .
A l a s t l e m m a b e f o r e w e p r o ve , t h a t t he ty p e c h a r a c t e r i z e s a c o n J u -
g a c y c l a s s :
3 ~ 6 I f T ( f ; ~ ) = T ( f ' ; ~ ' ) , t h e n t h e r e i s a ~ " E S s a t i s f y i n g
= ~ , ~ , ~ . - I a n d w i t h t h e p r o p e r t y , t h a t f o r e a c h c y c l i c
f a c t o r o f ~ t h e t w o c y c l e p r o d u c t s w i t h r e s p e c t t o f a n d w i t h
r e s p e c t t o f' a r e c o n j u g a t e s .~N
P r o o f : I f T ( f ; ~ ) = T ( f ' ; ~ ' ) w e o b t a i n f r o m 3 . 3 : ~ ~ ~' . H e n c e
t h e r e i s a ~ E S , w h i c h s a t i s f i e s
= ~ , ~ - 1 .
T h e s e t o f a l l t h e s e ~ f o r m s a r i g h t c o s e t o f t h e c e n t r a l i z e r o f
~ . S i n c e
( e ; ~ ) ( f ' ; ~ , ) ( e ; ~ ) - 1 = ( f ' ; ~ ) ,
3 . 5 i m p l i e s
T h e c y c l e p r o d u c t t o t h e f a c t o r ( j .. . r ( j ) ) o f ~ w i t h r e s p e c t t o
t h e m a p p i n g f i s
a n d w i t h r e s p e c t t o f ':
f . . . f r ( J ) ,
f, ...f, (j) •r ~
S i n c e ( I) i s v a l i d , t h e r e i s a ~ * f r o m t h e c e n t r a l i z e r o f ~ ,
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 49/197
4 4
w h i c h y i e l d s , i f i t i s a p p l i e d t o f' :
f' .... f' r -(J) ~ f' '' f r (j) "
T h u s ~ " := ~ * ~ f u l f i l s t h e s t a t e m e n t .
q . e . d .
N o w w e a r e r e a d y t o c h a r a c t e r i z e t h e c o n j u g a c y c l a s s e s ( S p e c h t ~ I ~ ):
3 . 7
P r o o f :
a ) I f ( f ; ~ ) N ( f ' ; ~ ' ) , t h e n t h e r e a r e f " a n d ~ " s o t h a t
C f. ;~ ,, )C f; ~) Cf ,, ;n ,, ) I = ( f , , ; 1 ) C e ; ~ , ) C f ; ~ ) C e ; ~ " ) - l c f " ; 1 ) - I
= ( f ' ; ~ ' ) ,
a n d u s i n g 3 . 5 w e o b t a i n T ( f ; ~ ) = T ( f ' ; ~ ' ) a s c l a i m e d .
b ) I f t h e o t h e r w a y r o u n d T ( f ; ~ ) = T ( f ' ; ~ ' ) , t h e n b y 3 . 6
t h e r e i s a ~ " E S s a t i s f y i n g ~ = ~ ,~ ,~ ,, -I . N o w
( e ; ~ , , ) ( f , ; ~ , ) ( e ; ~ , ) - 1 = ( f ~ , , ; ~ , ~ , ~ , - 1 ) = ( f ~ , ; ~ )
B e c a u s e o f 3 . 5 , t h i s i m p l i e s T ( f ' ; ~ ' ) = T(f~,,' ' ~) . A n d s i n c e
t h e s e t w o e l e m e n t s a r e c o n j u g a t e s , i t s u f f i c e s t o s h o w, t h a t
~•
C 2 3
W e a s s u m e n o w t h a t ~ " h a s b e e n c h o s e n i n s u c h a w a y , t h a t f o r
e a c h c y c l i c f a c t o r ( j . .. r ( j ) ) o f
f ' - - Z r C J ) ~
( c f . 3 . 6 ) .
L e t g j b e a n e l e m e n t o f G s u c h t h a t
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 50/197
4 5
o e ! ! •. f r ( J ) -- g j ( f ~ n . . . f r ( j ) l g ~ 1
H a v i n g c h o s e n s u c h a gj a n d s t a r t i n g w i t h u = 0 w e o b t a i n
f r o m t h e e q u a t i o n s
f ( - u ( j ) ) f ' ( ~ - u ( j ) ) g - l u I ( 2)g~-u( j) ~" - - (j)
e l e m e n t s g - u - 1 ( j ) ' w h i c h a r e u n i q u e l y d e t e r m i n e d (1 _(u_ (r), i f
gj = i s f i x e d .g ~ - o ( j )
H a v i n g d o n e t h i s f o r e v e r y c y c l i c f a c t o r o f ~ w e d e f i n e t h e
m a p p i n g f * : G ~ G b y
f*(i ) = gi' V i E ~ •
A n d t h i s m a p p i n g s a t i s f i e s
( f . ; l l ( f & . ; ~ ) ( f . ; l ) - I -- ( f . f & . f ~ - l ; ~ ) -- ( f; ~ )
( t h e l a s t e q u a t i o n f o l l o w s f r o m ( 2 )) , w h i c h p r o v e s ( I) •
q . e . d .
H e n c e G ~ S n c o n t a i n s e x a c t l y a s m a n y c o n j u g a c y c l a s s e s a s t h e r e
a r e t y p e s , i . e . ( s × n ) - m a t r i c e s ( a ik ) w h o s e e n t r i e s s a t i s f y 3 .3 .
F o r t h e n u m b e r o f t y p e s o r c o n j u g a c y c l a s s e s w e p r o v e n o w
( S p e c h t [ I ] ) :
~ 8 I f p ( m ) i s t he n u m b e r o f p a r t i t i o n s o f m f o r m E N a n d
p ( O ) : = I , t h e n u m b e r o f c o n J u g a c y c l a s s e s o f G ~ S n i s
Z P ( n l ) . . . p ( n s ) ,( n )
i f t he s u m i s t a k e n o v e r a l l t h e s - t u p e l s ( n ) = ( n l , . ° . , n s )
( s = n u m b e r o f c o n j u g a c y c l a s s e s o f G ) w i t h Z n i = n , 0 <_ n E 7 .
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 51/197
46
P r o o f : F o r a t y p e ( a i k ) w e d e f i n e n i : = ~. k a i k . T h e n ( n 1 , . . . , n s )k
i s s u c h a n s - t u p e l , a n d a l l t h e s - t u p e l s o c c u r i n t h i s w ay . n i
i s t h e s u m o f t h e e l e m e n t s o f th e i - t h r o w o f ( ai k ) w e i g h t e d w i t h
t h e i r c o l u m n n u m b e r . T h e r e f o r e i f t h e o t h e r r o w s a r e f i x e d, t h e r e
a r e e x a c t l y P ( n i ) p o s s i b i l i t i e s f o r t h e i - t h r o w t o b e t h e r o w o f
a t y p e. A n d t h i s p r o v e s t h e a s s e r t i o n .
q . e . d .
I f w e w i s h t o d e r i v e t h e o r d e r o f s u c h a c o n J u g a c y c l a s s, s a y o f
t h e c o n j u g a c y c l a s s o f G ~ S n w h i c h i s c h a r a c t e r i z e d b y t h e t y p e
a : = T a i k , l < k < n .
T h e n t h e r e a r e
e l e m e n t s o f t y p e ( a 1 , . . . , a n ) i n S . W e c h o o s e o n e o f t h e m , s a y ~ .
T h e a c y c l i c f a c t o r s o f ~ w h i c h a r e o f l e n g t h k c a n b e d i s t r i b u -
t e d i n t o t h e s c o n J u g a c y c l a s s e s o f G in
1 .... .
a l k l ~ " '" \ a s k = a l k ! . . . a s k !
w a y s w h i c h a r e in a c c o r d a n c e w i t h t h e c o n s i d e r e d t y p e ( a i k ) .
T, t f : G ~ G b e a m a p p i n g w h i c h y i e l d s s u c h a d i s t r i b u t i o n o f t h e
c y c l e p r o d u c t s . I t r e m a i n s t o s h o w, w h a t f r e e d o m o f c h o i c e i s l e f t
f o r c h o o s i n g t h e v a l u e s o f f .
T o a s s u r e t h a t
( a i k ) , w e s e t
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 52/197
47
f.. .f k_1(j) E C i
w e m a y c h o o s e t h e v a l u e s f ( j) , f ( ~ -1 ( j ) ) , . . . , f ( - k + 2 ( j ) ) a t
w i l l a n d c a n c h o o s e a n f ( ~ - k + 1 ( j ) ) E G s o t h a t t h e c o m p l e t e p r o -
d u c t i s a n e l e m e n t o f O i ~ G . H e n c e t h e r e e x i s t
akla l k ! . . . a s k ! = ( l e l k - l l c i l ) ~
m a p p i n g s f : ~ ~ G w h i c h d i s t r i b u t e t h e a k - c y c l e s o f ~ a s th e
c o n s i d e r e d t y p e ( a i k ) p r e s c r i b e s .
W e h a v e t o m u l t i p l y t h i s n u m b e r o f m a p p i n g s w i t h t h e n u m b e r o f
e l e m e n t s o f t y p e ( a l , . . . , a n ) a n d t a k e t h e p r o d u c t o v e r a l l i a n d
k t o o b t a i n t h e o r d e r o f t h e c o n j u g a c y c l a s s o f G ~ S n w h i c h i s
c h a r a c t e r i z e d b y t h e c o n s i d e r e d t y p e ( a i k ) . T h u s w e h a v e ( 8 p e c h t
[ 1 ] ) ,
3 ~ T h e c o n j u g a c y c l a s s o f G ~ S n c o n s i s t i n g o f t h e e l e m e n t s o f
t h e e l e m e n t s o f t y p e ( a ik ) h a s t h e o r d e r
t Q n l / T r a i k ! ( k l a l / I c i l ) a i ki , k
T h e r e f o r e t h e o r d e r o f t h e c e n t r a l i z e r o f a n e l e m e n t o f t y p e
(aik) is
i ~ a i k ! ( k l G l /I c i l ) a i k
B e f o r e w e c a n d e s c r i b e t h i s c e n t r a l i z e r i n de t a i l w e h a v e t o
c o n s i d e r t h e o r d e r s o f t h e e l e m e n t s .
A t f i r s t w e n o t i c e , t h a t f o r u E N :
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 53/197
4 8
3 . 1 o ( f ; ~ ) u = ( f f ~ . . . f u _ 1 ~ u ) ,
w h a t i m p l i e s , t h a t t h e o r d e r o f ( f ;~ ) i s a m u l t i p l e o f t h e o r d e r
o f ~. T h e o r d e r o f ~ is t h e l e a s t c o m m o n m u l t i p l e o f t h e l e n g t h s
o f t h e c y c l i c f a c t o r s o f ~ ( of . 1 . 1 1 ) .
O n t h e o t h e r h a n d w e l e t u E N b e a m u l t i p l e o f t he l e n g t h o f
e v e r y c y c l i c f a c t o r o f ~. I f i E ~, t h e n t h e r e i s s u c h a v _ >O t h a t
i = ~ v ( j ) a n d j i s t h e l e a s t s y m b o l o f t h e c y c l i c f a c t o r o f
w h i c h i n c l u d e s t h i s s y m b o l i. L e t g b e t h e c y c l e p r o d u c t a s s o c i a t e d
w i t h t h i s c y c l e a n d w i t h r e s p e c t t o f . T h e n w e h a v e
f . . . f u _ 1 ( i ) = f C ~ V ( j ) ) f ( ~ v - I C j l ) . . . f C ~ v - u + 1 ( j ) )
3.11= f Q ~ v ( j ) ) . . . f ( ~ ( j ) ) g . f ( ~ ( j ) ) - 1 . . . f t ~ v t j ) ) - 1 .-- . . - - - - . . . . . . - . . . g W ,
i f u = w r f o r t h e l e n g t h r o f t h e c y c l e i n c l u d i n g i .
T h e o r d e r o f ( f ; ~) i s t h e m i n i m a l u E N so t h a t u = I S n a n d
f . . . f u _ 1 ( i ) = IG , V i E S , i . e . f ' ' ' f ~ u - 1 = e. H e n c e f r o m
3 . 1 1 w e o b t a i n
5 . 1 2 T h e o r d e r o f ( f ; ~) ( o f t y p e ( a i k )) i s t h e l e a s t c o m m o n m u l -
t i p l e o f t h e p r o d u c t s k m i o f t h e l e n g t h s k o f t h e c y c l i c
f a c t o r s o f ~ w i t h t h e o r d e r s w i o f t h e c o r r e s p o n d i n g c y c l e -L , ,
p r o d u c t s w i t h r e s p e c t t o f:
l < ( f ; ~ )> l = 1 . c . m . { k . i ] .
i , k : a i k > O
H e n c e ( f ;~ ) i s p - r e g u l a r ( i . e. p ~ l < ( f ; ~ ) > l ) i f p d o e s n o t d i -
v i d e a n y o n e o f t h e s e p r o d u c t s k w i. We h a v e t h e f o l l o w i n g c o r o l -
l a r y :
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 54/197
49
3 ~ T h e p - r e g u l a r c l a s s e s o f G ~ S n a r e e x a c t l y t h e c o n j u g a c y c l as -
s e s b e l o n g i n g t o t y p e s ( a i k) w h e r e n o n v a n i s h i n g e n t r i e s o c c u r
o n l y i n r o w s t o p - r e g u l a r c l a s s e s C i o f G a n d c o l u m n s w i t h
p - r e g u l a r n u m b e r s k .
T h e p - c l a s s e s c o r r e s p o n d t o t h o s e t y p e s ( a ik ) w h e r e o n l y i n
c o l u m n s w i t h p - p o w e r - n u m b e r s k a n d o n l y i n r o w s b e l o n g i n g t o
p - c l a s s e s C i o f G d o v a n i s h i n g e n t r i e s o c c u r .
T h e r e m a i n i n g C y p es b e l o n g t o p - s i n g u l a r c l a s se s .
3 . 1 2 a n d 3 . 1 3 a re g e n e r a l i z a t i o n s o f 1 .1 1 a n d 1 . 1 2 : f o r G = { 1 } ,
i . e . f o r o n e - r o w e d t y p e s w e o b t a i n 1 .1 1 an d 1 . 1 2 a t o n c e .
A s i s w e l l - k n o w n , t h e n u m b e r o f r e p r e s e n t a t i o n s o f a f i n i t e g r o u p
o v e r t h e f ie l d o f c o m p l e x n u m b er s w h i c h h a v e r e a l c h a r a c t e r i s
e q u a l t o t h e n u m b e r o f a m b i v a l e n t c o n j u g a c y c l a s s e s ( i. e. c l a s s e s
c o n t a i n i n g t h e i n v e r s e o f e a c h o f i t s e l e m e n t s ) . A s w e h a v e s e e n
i n s e c t i o n 1 , e a c h c o n j u g a c y c l a s s o f a s y m m e t r i c g r o u p i s a m b i -
v a l e n t , w h i l e o n l y t h e a l t e r n a t i n g g r o u p s A t , A 2 , A 5, A 6 , A I O a n d
A 1 4 a r e a m b i v a l e n t ( cf . 1 . 1 5 / 1 . 2 5 ) . T h i s i m p l i e s t h a t a l l t h e o r -
d i n a r y c h a r a c t e r s o f S a n d a l l t h e o r d i n a r y c h a r a c t e r s o f t h e s e
s i x a l t e r n a t i n g g r o u p s a r e r e a l . W e s h o w, t h a t t h i s i s th e c a s e
for G~Sn, too, if it is val id fo r G (Kerber [7]):
~ . 1 5 I f G i s a m b i v a l e n t , t h e n G ~ S n i s a m b i v a l e n t .
P r o o f : T h e r e i s o b v i o u s l y a 1 - 1 - c o r r e s p o n d e n c e b e t w e e n t h e c y c l e s
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 55/197
5O
( j . . . r ( j ) ) o f ~ a n d ( j .. . - r ( j ) ) o f - 1 .
L e t g b e t h e c y c l e p r o d u c t t o ( j. . . r ( j ) ) w i t h r e s p e c t t o f.
T h e n t h e o y c l e p r o d u c t t o ( j. . . - r (j ) ) w i t h r e s p e c t t o f - ~ 1 i s
( r e c a l l t h a t ( f ; ~ ) - 1 = ( f - 1 1 | ~ - I ) )-
I f n o w G i s a n a m b i v a l e n t g r o u p , t h e n g ~ g -l , y g E G , w h a t i m -
p l i e s , t h a t i n t h i s c a s e
A n d t h i s p r o v e s t h e a s s e r t i o n s i n c e t w o e l e m e n t s o f t h e s a m e t y p e
a r e c o n j u g a t e s ( o f. 3 . 7 ) .
q . e . d .
A s p e c i a l c a s e i s
V m , n : S m ~ S n i s a m b i v a l e n t .
3 . 1 4 / 3 . 1 5 g e n e r a l i z e a r e s u l t o f B e r g g r e n ( B e r g g r e n [ 1] ). H e
p r o v e d t h e a m b i v a l e n c y o f G ~ S 2 a s s u m i n g t h a t G i s a m b i v a l e n t .
U s i n g t h i s a n d t h e a s s o c i a t i v i t y o f t h e w r e a t h p r o d u c t m u l t i p l i -
c a t i o n h e sh o w e d , t h a t t h e 2 - S y l o w - e u b g r o u p s o f s y m m e t r i c g r o u p s
a r e a m b i v a l e n t . A n d t h i s i m p l i e s, t h a t e v e r y 2 - g r o u p c a n b e e m -
b e d d e d i n a n a m b i v a l e n t 2 - g r o u p .
C y c l i c g r o u p s C p o f o r d e r p a r e n o t a m b i v a l e n t i n g e n e r a l , t h e r e -
f o r e t h a t n o t e v e r y p - S y l o w - s u b g r o u p o f S i s a m b i v a l e n t i s i m -
p l i e d b y t h e f o l l o w i n g :
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 56/197
5 1
T h e a m b i v a l e n c y o f G ~ H i m p l i e s t h e a m b i v a l e n c y o f G a n d t h e
a m b i v a l e n c y o f H .
P r o o f : I f G ~ H i s a m b i v a l e n t , t h e n f o r e v e r y ( f ; ~ ) E G ~ H t h e r e i s
a n ( f ' ; ~ ' ) s o t h a t
( f , ; ~ , ) C f ; ~ ) C f , ~ , ) - 1 = ( f , f , f , - 1, ~ , _ 1 ; ~ ' ~ ' - I) = ( f- 11 1~ -I ). (I )~ _
T h i s i m p l i e s , t h a t e v e r y ~ E H i s c o n j u g a t e t o i t s i n v e r s e ,
i . e . H is a m b i v a l e n t .
A n d i f w e c h o o s e a c o n s t a n t f : ~ ~ G , s a y
f( i) = g, ¥ i E G,
t h e n f o r ~ = I w e o b t a i n f r o m ( I ), t h a t t h e r e i s a n f' s o t h a t
f , f f , - 1 = f - 1 w h a t i m p l i e s g N g - 1 . G h a s t o b e a m b i v a l e n t a s w e l l .
q . e . d .
U s i n g 1 . 2 5 w e h a v e t h e c o r o l l a r y :
A i ~ S m a n d S m ~ A i w i t h i E { 1 , 2 , 5 , 6 , 1 0 , 1 4 } a r e t h e o n l y a m b i -
v a l e n t w r e a t h p r o d u c t s o f a l t e r n a t i n g w i t h s y m m e t r i c g r o up s .
B e f o r e w e c o n c l u d e t h i s s e c t i o n w i t h a n e x a m p l e l e t u s d e s c r i b e
t h e c e n t r a l i z e r o f a n e l e m e n t ( f ;~ ) E G ~ S n .
A s i n t h e c a s e o f t h e d e s c r i p t i o n o f t h e c e n t r a l i z e r o f a p e r m u -
t a t i o n i n S ( cf . s e c t i o n 2 , 2 . 3 1 / 2 . 3 2 ) w e s t a r t w i t h t h e c o n s i -
d e r a t i o n o f a s p e c i a l c a s e:
( f l ~ ) E e ~ s n , T ~ = ( 0 , . . . , 0 , I ) ,
i . e . ~ i s a c y c l e o f l e n g t h n .
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 57/197
52
I n t h i s c a s e t h e t y p e ( a ik ) o f ( f ; ~) h a s e x a c t l y o n e n o n v a n i s h i n g
e n t r y , a I i n t h e l a s t c o l, ~m n.
S i n c e t h e c e n t r a l i z e r s o f c o n j u g a t e s a r e c o n j u g a t e s u b g r o u p s , w e
c a n a s s u m e , t h a t
(f;1) E G 1, i.e. f(i ) = 1 , V i ~ I, f(1 ) E C i,
i f a i m i s t h i s o n l y n o n v a n i s h i n g e n t r y o f ( a i k ).
A s u b g r o u p o f t h e c e n t r a l i z e r o f (f ; ~) i s t h e c y c l i c s u b g r o u p
< ( f ; ~ ) > ~ G % S n , g e n e r a t e d b y ( f; ~ ) i t s e l f . B u t ( f ; ~ ) c o m m u t e s
a l s o w i t h t h e e l e m e n t s ( f '; 1 ) E G * w h o s e m a p p i n g s f ' a r e c o n s t a n t
o n g a n d s o t ha t t h e i r v a l u e i s a n e l e m e n t o f t he c e n t r a l i z e r
o f f ( 1 ) i n G :
f ' : f ' ( i ) = g E C G ( f ( 1 ) ) , V i E ~ -
T h i s f o l l o w s f r o m
( f ' ; 1 ) ( f ; ~ ) ( f ' ; 1 ) - 1 = ( f , ff ~ - 1 ;~ ) = ( f , f f , - 1 ) = ( f; ~) •
T h e s u b g r o u p o f t h e s e ( f ' ;1 ) i s t h e d i a g o n a l o f t h e b a s i s g r o u p
o f t h e s u b g r o u p C G ( f ( 1 ) ) ~ S n ~ G ~ S n :
{ ( f ' ; 1 ) } = d i a g ( G G ( f ( 1 ) ) * ) ~ G G ( f ( 1 ) ) * ~ G * .
L e t u s m u l t i p l ~ t h e s e t w o s u b g r o u p s o f t h e c e n t r a l i z e r a n d w e
o b t a i n
3 . 1 8 d i a g ( G G ( f ( 1 ) ) * ) < ( f ; ~ ) > .
W e w o u l d l i k e t o s h o w, t h a t t h i s i s a s u b g r o u p a n d o f t h e s a m e
o r d e r a s C G ~ S n ( f ; ~ ) a n d h e n c e e q u a l t o t h i s c e n t r a l i z e r .
I f ( f ' ; 1 ), ( f " ;1 ) E d i a g ( C G ( f ( 1 ) ) * ) , w e h a v e f o r r, s E Z :
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 58/197
53
( f , ; 1 ) ( f ; ~ ) r ( ( f . ; 1 ) ( f ~ ) s ) - I = ( f , ; 1 ) ( f ; ~ ) r - s ( f . - 1 ; 1 )
= ( f , f , , - 1 ; 1 ) ( f ; ~ ) r - s .
H e n c e t h i s s u b s e t 3 . 1 8 i s a s u b g r o u p .
I f w e n o w a s s u m e , t h a t
( f , ; 1 ) ( f ; ~ ) r = ( f . ~ 1 ) C f ~ ) s
w e h a v e
( f . - I f , ; 1 ) = ( f ; ~ ) s - r .
T h i s i s f u l f i l l e d o n l y i f s - r m 0 ( n ) .
O n t h e o t h e r h a n d w e h a v e
( f ; ~ ) n = ( ff . . . f n _ 1 ; ~ n ) = ( f ( 1 ) , . . . , f ( 1 ) ; 1 ) E d i a g ( C G ( f ( 1 ) ) . )
a n d h e n c e i f r m t ( n) t h e r e i s a n ( f ' ; 1 ) E d i a g ( C G ( f ( 1 ) ) * )
s a t i s f y i n g
( f ; ~ ) r = ( f , ; l l C f ; ~ ) t .
T h u s t h e o r d e r of t h is s u b g r o u p o f C G ~ S n ( f ; ~ ) i s
l a l a g C % ( f C 1 l l * l < C f ~ l > l = C I Q J / l c i l l n ,
a n d t h i s i s t h e o r d e r o f t h e c e n t r a l i z e r o f ( f ; ~ ) , a s c a n b e
s e e n f r o m 3 . 9.
T h e r e f o r e w e h a v e p r o v e d t h e f o l l o w i n g f i r s t s t e p t o w a r d s a
c o n s t r u c t i o n o f t h e c e n t r a l i z e r o f a g e n e r a l e l e m e n t o f G ~S n
(O re [I ]) :
I f ~ i s a n n - c y c l e a n d ( f ; 1) E G I , t h e n t h e c e n t r a l i z e r o f
( f ;~ ) i n G ~ S n i s t h e p r o d u c t o f t h e d i a g o n a l s u b g r o u p o f
t h e b a s i s g r o u p C G ( f ( 1 ) ) ~ o f C G ( f ( 1 ) ) ~ S n _( G ~ S n a n d t h e
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 59/197
5 4
c y c l i c s u b g r o u p g e n e r a t e d b y ( f ; ~ ) , i .e .
C G ~ S n C f ; u ) = d i a g ( C G C f C 1 ) ) * ) < C f ; ~ ) >
i n t h i s s p e c i a l c a s e .
U s i n g t h i s w e w o u l d l i k e t o d e s c r i b e t h e c e n t r a l i z e r o f a g e n e r a l
e l e m e n t ( f ; ~ ) E G ~ S n .
Le t u s den ote by ~J k (1--<J--<aik) the ai k cyc lic fa ct ors of a who se
o y c l e p r o d u c t e w i t h r e s p e c t t o f a r e e l e m e n t s o f C _~ G ( i f a i k > O ) .
T, t ~i k b e the cyc le
3 . 2 0 ~ J k = ( r J ~ ( r J k ) . . . ~ k - X ( r J k ) )
s o t h a t riJ i s t h e l e a s t s y m b o l o f t h i s c y c l e .
W e n o t i c e t h a t
3.21 ~ = i,~ ,k ~Jik "
W i t h o u t l o s s o f g e n e r a l i t y w e c a n a s s u m e , t h a t f i s o f t h e f o l l o w -
i n g f o r m :
. . = f ( - k + 1 ( r j k ) ) I Q .. 2 2 f ( r ~ k ) E C , f ( ~ - l ( r ~ k ) ) = . =
I f w e n o w d e f i n e a m a p p i n g f Ji k: ~ ~ G b y
f ( r J k ) rJik
= = I i f s =
1G e l s e w h e r e ,
t h e n
3 . 2 4
a n d t h e s e f a c t o r s ( fJ . ~J ~i k' i k " a r e c o m m u t a t i v e s i n c e t h e y h a v e d i s -
j o i n t c y c l i c f a c t o r s i f w e l o o k a t t h e p e r m u t a t i o n r e p r e s e n t a t i o n
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 60/197
55
of G~S .
R e g a r d e d a s e l e m e n t s o f s u b g r o u p s o f t h e f o r m
(G × G = ( r ) x . . . x G k _ l ( r ) ) S ~ ~ G~Sk
t h e n f a c t o r s f fJ - ~J ~ a r e e l e m e n t s o f t h e s p e c i a l f o r m w h o s eik' ik S
c e n t r a l i z e r s w e r e d e s c r i b e d i n 3 . 19 . U s i n g t h e s a m e a r g u m e n t a s
i n s e c t i o n 2 t o g e t t h e c e n t r a l i z e r o f a g e n e r a l p e r m u t a t i o n w e
obtai n from 3.19 and 3.24 (Ore [1]):
3 ~ I f T ( f ; ~ ) = ( a i k ) t h e n t h e c e n t r a l i z e r o f ( f ;~ ) i n G ~ S n i s
a s u b g r o u p c o n j u g a t e t o t he c e n t r a l i z e r
o f t h e s p e c i a l e l e m e n t 3 . 2 4 o f t h i s t y pe ( s e e 3 .2 0 - 3 . 2 4 ) .
It is easy to check, tha t this agrees wi th 3.9, and th at for
G = [1} we g et 2.32 .
E x a m p l e . T o c o n c l u d e t h i s s e c t i o n , w e c o n s i d e r a s u b g r o u p o f S 6 ,
w h i c h i s a f a i t h f u l p e r m u t a t i o n r e p r e s e n t a t i o n o f S 3 %S 2 :
( [ 1 , ( 1 2 ) , ( 1 3 ) , ( 2 3 ) , ( 1 2 3 ) , ( 1 3 2 ) ] x [ 1 , ( 4 5 ) , ( 4 6 ) , ( 5 6 ) , ( 4 5 6 ) , ( 4 6 5 ) ] )
• [ 1 , ( 1 4 ) ( 2 5 ) ( 3 6 ) ] ~ S6 •
W e w o u l d l i k e t o d e s c r i b e i t s c o n J u g a c y c l a s s e s t o i l l u s t r a t e
3 . 7 a n d g i v e a c o m p l e t e s y s t e m o f r e p r e s e n t a t i v e s o f t h es e
c l a s s e s . T h i s w e s h a l l d o a c c o r d i n g t o t h e o r d e r i n g
0 1 : = [ 1 3 , C2 := [ ( 1 2 ) , ( 1 3 ) , ( 2 3 ) ] , C3 := [ ( 1 2 3 ) , ( 1 3 2 ) ]
o f t h e c o n j u g a c y c l a s s e s o f S .
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 61/197
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 62/197
5?
c l a s s o f S 3 % S 2 .
B e c a u s e o f 3 . 9 t h e o r d e r o f t h i s c l a s s i s
7 2 / ( 3 ! / 1 ) 1 ( 3 : / 3 ) 1 = 6 .
( i i i ) ( ( 1 2 3 ) , I ; I ) i s o f t y p e . A r e p r e s e n t a t i v e e l e m e n t o f
t h i s c o n J u g a c y c l a s s i s ( 12 3) E S a s c a n b e s e e n a n a l o g o u s l y6
t o ( i i) . T h e o r d e r o f t h i s c l a s s i s 4.
( iv ) ( 2 ), ( 12 ) ; ) i s o f t y p e . A p e r m u t a t i o n r e p r e s e n t i n g
t h i s c o n J u g a c y c l a s s i s ( 1 2 ) ( 4 5 ) , t h e c l a s s i s o f o r d e r 9 .
( v) T ( ( 1 2 3 ) , ( 1 2 3 ) ; 1 ) = . h i s c l a s s i s o f o r d e r ¢ a n d r e -
p r e s e n t e d b y ( 12 3 ) ( 4 5 6 ) .
( v i ) ~ ( 1 , 1 ~ ( 1 2 ) ) = . ( 1 , 1 ~ ( 1 2 ) ) is mapped onto ( 1 4 ) ( 2 5 ) ( 3 6 ) ,
h e n c e t h i s p e r m u t a t i o n i s a r e p r e s e n t a t i v e e l e m e n t o f t h i s
c o n j u g a c y c l a s s o f o r d e r 6 .
( v i i ) T ( ( 1 2 ) , ( 1 2 3 ) ; 1 ) = . h e i m a g e o f t h i s c l a s s o f $ 3 ~ S 2
c o n t a i n s ( 1 2 ) ( 4 5 6 ) , a n d i ts o r d e r i s 1 2 .
( v i i i ) T h e c y c l e p r o d u c t b e l o n g i n g t o t h e p e r m u t a t i o n o f ( ( 1 23 ) ,
( 1 2 3 ) ; ( 1 2 ) ) i s
( 1 2 ) ~ f ( 1 ) f ( 2 ) = ( 1 3 2 ) ,
h e n c e
T ( ( 1 2 3 ) , ( 1 2 3 ) ; ( 1 2 ) ) = l i ! ] "
T h e i m a ge u n d e r t h e p e r m u t a t i o n r e p r e s e n t a t i o n i s
f ( 1 ) a f ( 2 ) o - 1 ( 1 2 ) * = ( 1 2 3 ) ( 4 5 6 ) ( 1 4 ) ( 2 5 ) ( 3 6 ) = ( 1 5 34 2 6 ) •
T h e o r d e r o f t h i s c l a s s i s 1 2.
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 63/197
58
( ix ) T ( ( 1 2 ) , ( 1 2 3 ) ; ( 1 2 ) ) = . h e i m a g e is ( 1 5 ) 6 2 6 3 ¢ ) , t h e o r-
der of the class is 18.
T h e s e c a l c u l a t i o n s w i l l b e o f us e l a t e r o n f o r t he e v a l u a t i o n o f
t h e c h a r a c t e r t a b l e o f $ 3 ~ S 2. I t w i l l b e u s e f u l f o r t h e s e c a l c u -
l a t i o n t o o b s e r v e , t h a t t h e g r o u p s S m ~ S n p o s s e s s t w o n o r m a l d i v i -
s o r s o f i n d e x 2 : S m % S n + : = S m ~ S n G A m m a n d S m~ =~ . H a v i n g n o t i c e d
t h i s w e o n l y n e e d t o e v a l u a t e a s m a l l p a r t o f t h e c h a r a c t e r t a b l e
a n d t h e n u s e t h e s y m m e t r i e s a r i s i n g f r o m t h i s f a c t.
T h u s i t i s h e l p f u l t o h a v e t h e r e p r e s e n t a t i v e s o f t h e c o n j u g a c y
c l a s s e s i n p e r m u t a t i o n a l f o r m a s w e l l a s i n t h e f o r m ( f ;~ ) a s i n
o u r e x a m p l e . W e s e e a t o n ce t h a t t h e c o n j u g a c y c l a s s e s d e s c r i b e d
in (i), (iii), (iv), (v) and (ix) are the clas ses co nsi sti ng of
p e r m u t a t i o n s a n d h e n c e t h e s e c l a s s e s f o r m $ 3 ~ $ 2 + . ~ o r e o v e rv e n
the class es (i), (ii), (iii), (iv), (v) and (vii) are the cla sse s
c o n s i s t i n g o f e l e m e n t s o f t h e f o r m ( f ;1 ) a n d h e n c e t h e y b u i l d u p
t h e n o r m a l d i v i s o r S 3 ~ A 2 = $ 3 ~ I ] = S ~ ~ S 3 x S 3 .
W e h a v e n o w f i n i s h e d s u m m a r i z i n g t h e g r o u p - t h e o r e t i c a l r e s u l t s
w h i c h w e n e e d t o d e s c r i b e t h e r e p r e s e n t a t i o n t h e o r y o f t h e s ym -
m e t r i c a n d a l t e r n a t i n g g r o u p s a s w e l l a s o f w r e a t h p r o d u ct s .
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 64/197
C h a p t e r I I
R e p r e s e n t a t i o n s o f w r e a t h p r o d u c t s
W e w o u l d l i k e t o d e s c r i b e t h e r e p r e s e n t a t i o n s o f w r e a t h p r o d u c t s ,
e s p e c i a l l y o f w r e a t h p r o d u c t s G ~ S n w i t h s y m m e t r i c g r o u p s .
A f i r s t s e c t i o n c o n t a i n s a p r e p a r a t o r y s ~ m m a r y o f t he o r d i n a r y
r e p r e s e n t a t i o n t h e o r y o f th e s y m m e t r i c g r o u p. T h e f o l l o w i n g
s e c t i o n c o n t a i n s t h e r e p r e s e n t a t i o n t h e o r y o f w r e a t h p r o d u c t s
o f f i n i t e g r o u p s o v e r a n a l g e b r a i c a l l y c l o s e d f i e l d.
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 65/197
6 O
4 . T h e o r d i n a r y i r r e d u c i b l e r e p r e s e n t a t i o n s
o f th e s y m m e t r i c g r o u p
T h e g r o u n d f i e l d i s t h e f i e l d C o f c o m p l e x n u m b e r s . S i n c e C i s a l -
g e b r a i c a l l y c l o s e d an d o f c h a r a c t e r i s t i c z e r o, t h e n u m b e r o f i r -
r e d u c i b l e C - r e p r e s e n t a t i o n s o f S i s e q u a l t o t h e n u m b e r o f c o n -
j u g a c y c l a s s e s o f S n -
A s w e h a v e s e e n i n t h e f i r s t s e c t i o n , t h e r e i s a l - l - c o r r e s p o n -
d e n c e b e t w e e n th e c o n j u g ~ c y c l a s s e s o f S a n d th e p a r t i t i o n s
a = ( ~ 1 , . . . , ~ h ) , a E N , ~ j A a j + 1 ( 1~ j< _h -1 ), Z a i = n
o f n .
H e n c e i f w e c a n a s s o c i a t e w i t h e a c h of t h e s e p a r t i t i o n s a n
i r r e d u c i b l e C - r e p r e s e n t a t i o n o f S s o t h a t r e p r e s e n t a t i o n s a s s o -
c i a t e d w i t h d i f f e r e n t p a r t i t i o n s a r e i n e q u i v al e n t , w e h a v e a
c o m p l e t e s y s t e m o f i r r e d u c i b l e C - r e p r e s e n t a t i o n s o f S n -
H o w t h i s c a n b e d o n e w e s h a l l d e s c r i b e n o w . T h e p r o c e d u r e u s i n g
a c o n s i d e r a t i o n o f p r i m i t i v e i d e m p o t e n t s o f t h e g r o u p a l g e b r a i s
w e l l k n o w n , b u t a v e r y u s e f u l h i n t t o c l a r i f y t h i s p r o c e s s b y
u s i n g M e c k e y ' s i n t e r t w i n i n g n u m b e r t h e o r e m w e ow e to A . J. C o l e -
m a n ( C o l e m a n [ 1] , c f . a l s o B a y a r [ I ], B u r r o w [1 ] , [ 2 ] , G t h n d Gz a l p
[ 1] , M a l z a n [ I] , M u n k h o l m [ I] , a n d th e h i n t f o l l o w i n g 2 . 2 9 i n
R o b i n s o n [ 5] ).
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 66/197
61
T o g e l h e r w i t h a p a r t i t i o n ~ w e c o n s i d e r t h e Y o u n g - d i a g r a m
.
. . . . . . . . . . a I o d e s
• . . . . . a n o d e s
[ a S :e e e e e e e e e e e e
. . . . . ~ h n o d e s
( cf . s e c t i o n I) a n d i t s f i r s t Y o u n g - t a b l e a u
I 2 .. . . . . . . . . . . a 1
a . ~ 1 + 1 ¢ 1 + 2 " ' " a l + a 24.1 T 1 .= . . . . . . . . . . . . . . .
e e e e e e n
a n dt f o l l o w s f r o m t h e r e s u l t s o f s e c t i o n I, t h a t t h e g r o u p s H I
aV 1 o f t h e h o r i z o n t a l a n d v e r t i c a l p e r m u t a t i o n s o f T ~ a re Y o u n g
s u b g r o u p s w i t h t h e p r o p e r t y
4 . 2 H 1 n V ; = [ 1 } .
a a n d b ye t u s d e n o t e b y I H ~ t he i d e n t i t y r e p r e s e n t a t i o n o f H I
a d e f i n e d b yV ~ t h e a l t e r n a t i n g r e p r e s e n t a t i o n o f V 1 '
= = ( 1 ) , v
Va+.4. 3 (I) , V ~ E -I °= VI N A
:=
( - 1 ) , V ~ e - 1 " 1 "
I f I H ~ t S a n d A V ~ t S a r e t h e r e p r e s e n t a t i o n s o f S i n d u c e d
b y I H ~ a n d A V e , t h e f o l l o w i n g i s t h e c r u c i a l t h e o r e m :
4 , 4 I H ~ ~ S a n d A V ~ t S h a v e e x a c t l y o n e i r r e d u c i b l e c o n s t i t u -
e n t i n c o m m o n , i n e a c h c a s e w i t h m u l t i p l i c i t y I.
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 67/197
62
P r o o f : T h e a s s e r t i o n i s f u l f i l l e d i f a n d o n l y i f t h e i n n e r p r o -
d u c t ( I H ~ t S , A V ~ ~ S n) o f t h e c o r r e s p o n d i n g c h a r a c t e r sI H V t S A V ~ t S
X a n d X s a t i s f i e s
4 . 5 ( I H ~ t S n , A V ~ t S ) = 1
( s e e C u r t i s / R e i n e r [ I] , E x . 3 1 . 1 ) . ~ o r t h e i n n e r p r o d u c t i s d e -
f i n e d b y
A ~( I H Sn, V 1 t S ) : =
Z x I H 1 t S n ( ~ ) A V 1 1 S n ( ~ - 1 )
a n d h e n c e 4 . 5 i m p l i e s t h e a s s e r t i o n b e c a u s e o f t h e o r t h o g o n a l i t y
r e l a t i o n s o f t h e i r r e d u c i b l e c h a r a c t er s .
T o p r o v e 4 . 5 w e n o t i c e , t h a t t h i s i n n e r p r o d u c t i s t h e i n t e r t w i -
n i n g n u m b e r of t h e tw o i n d u c ed r e p r e s e n t a t i o n s . H e n c e u s i n g
M a c k e y ' s i n t e r t w i n in g n u m b e r t h e o r e m ( C u r t i s ~ e i n e r [ I ], ( 44 . 5) )
w e o b t a i n
( I H ~ t S n , A V ~ t S ) = i ( I E ~ r S n , A V V r S n )
: ~ i ( I H ~ ~ E l n~ V l ~ - 1 , ( A V ~ ) ~ ~ l n ~ V l~ - I ) ,
H I ~ V 1
i f t h e s u m i s t a k e n o v e r a c o m p l e t e s y s t e m o f p a i r w i s e d i f f e r e n t
a ~ ~ ~n S n, i f "~ " m e a n s r e s t r i c t i o nd o u b l e c o s e t s H I ~ V I o f H I a n d V I
a n d i f w e d e n o t e b y ( AV e) ~ t h e r e p r e s e n t a t i o n ( o f ~ V V ~ - I) c o n j u -
g a t e t o A V V a n d d e f i n e d b y
( A V ) ~ ( ~ ' x - I) : = A V ( ~' ), V ~ ' E V I •
N o w th e i n t e r s e c t i o n H ~ ~ ~ -I i s o b v i o u s l y a d i r e c t p r o d u c t o f
s y m m e t r i c s u b g r o u p s , s a y
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 68/197
6 3
H I G ~ V - 1i , j 8 z i j
( cf . 1 . 3 1 ) . A n d t h e r e f o r e t h e r e s t r i c t i o n
I H ~ ~ ~ - ~ 1 . ~ V l -I = I ( H ~ N ~ V ~ - I )
i s e q u a l t o t h e r e s t r i c t i o n
( A V ~ ) ~ $ H I N ~ V I~ -I = A ( H ~ G ~ V ~ - I )
i f a n d o n l y i f z i j ~ 1 , V i , j , i . e . i f a n d o n l y i f
H ~ R ~ V ~ - 1 = [ 1 ] .
H e n c e
: 1~ -1
= { I, i f H I ~ V I ~ = {I ]
0 o t h e r w i s e .
F r o m 1 . 3 5 w e k n o w , t h a t t h e r e i s e x a c t l y o n e d o u b l e c o s e t
m ~ ~ -1H I ~ V 1 w i t h t h e p r o p e r t y H I N ~ V I ~ = [ I ] ( n a m e l y t h e d o u b l e c o s e t
H I~ V~ , s e e 4 . 2 ) . T h i s i m p l i e s 4 . 5 a n d t h e t h e o r e m i s p r o v e d .
q . e . d .
L e t u s d e n o t e b y [ ~] t h e e q u i v a l e n c e c l a s s o f t h is u n i q u e l y d e -
t e r m i n e d c o m m o n c o n s t i t u e n t :
[~] := IH~ t S n AV ~ t S •
S i n c e w i t h t h e n o t a t i o n (I n ) : = ( I , . . . , I ) w e h a v e
IH~ ln) = I{1] = AV~ n) ,
t h e i n d u c e d r e p r e s e n t a t i o n I H~ l n) ~ S a s w e l l a s A V ~ n ) t 8 i s
t h e r e g u l a r r e p r e s e n t a t i o n R S n o f 8 . T h u s
IH~ ln) ~ S O (AV~ ln) t S = AS n) = RS n G AS n = AS n,
(IH~n) ~ Sn = IS ) ~ AV~ n) ~ S = ISn O RS n = IS .
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 69/197
6 4
U s i n g n o t a t i o n 4 . 6 w e g e t t h e r e f r o m:
~ - 7 I n ] = I s n , [ 1 n ] = A S n •
L e t u s d e n o t e b y " @" t h e o u t e r t e n s o r p r o d u c t m u l t i p l i c a t i o n
( f o l l o w i n g t h e n o t a t i o n o f O u r t i s / R e i n e r [ 1] , c f. % 4 3) a n d s u b s t l -
a a n d V ~ W e o b t a i nu t e 8 a n d 8 a, f o r t h e i s o m o r p h i c s u b g r o u p s H I
f r o m 4 . 7 :
4 .8 z s ~ = [ ~ 1 ] ~ ' " ~ [ % ] = ~ [ ~ i ] ,, i a'
A S a , = [ 1 a ' ~ ] , . . . @ [ 1 c r '~ ' ] = @ [ 1 3 . ] •i
T h e i n d u c e d r e p r e s e n t a t i o n s w i l l b e d e n o t e d a s f o l l o w s :
V [ a i ] = [al ]''" [@h] := (~i ~i]) f Sn '
a ' a ' a :
" [ ~ [ 1 3 . ] = [1 1 ] . . . [ 1 a ] ~ ' ' ] : = ( @ [ l i 1 ] ) f S n •
T h e r e f o r e a s e c o n d f o r m u l a t i o n o f 4 . 6 is ( cf . R o b i n s o n [ 5 ] , 2 . 2 9 ):
4 , 1 0
~ I I[ a ] = [ a 1 ] . . . [ a l : l ] 13 [ 1 1 ] . . . [ 1 ~ h ' ] •
U s i n g a g a i n t h e n o t a t i o n o f C u r t i s / R e i n e r [ I] w e d e n o t e b y " @ "
t h e i n n e r t e n s o r p r o d u c t m u l t i p l i c a t i o n . B y d e f i n i t i o n o f th e a l -
t e r n a t i n g r e p r e s e n t a t i o n w e h a v e
[ 1 n ] ® [ 1 n ] = [ n ] .
H e n c e
[a'] = IS~, t S n AS a ~ S = (AS a,~S n n ISa ~S n) @ [In],
t h u s
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 70/197
65
4.11 [ a ' ] = [ ~ ] @ [1 n ] •
T h i s m e a n s , t h a t th e r e p r e s e n t a t i o n s [ ~ ] and [ ~ ' ] d i f f e r o n l y o n
t h e o d d p e r m u t a t i o n s a n d t h e r e o n l y i n t h e s ig n .
4 . 6 c h a r a c t e r i z e s c e r t a i n i r r e d u c i b l e C - r e p r e s e n t a t i o n s o f Sn ,
a n d we w o u l d l i k e t o s h o w t h a t t h e s y s t e m o f t he s e r e p r e s e n t a t i o n s
[ m] i s a c o m p l e t e s y s t e m o f p a i r w i s e i n e q u i v a l e n t i r r e d u c i b l e
C - r e p r e s e n t a t i o n s ( o r o rd i n a r y r e p r e s e n t a t i o n s a s t h e y a r e a l s o
called) of S n-
~ o p r o v e t h i s i t s u f f i c e s - a s h a s b e e n s a i d a t t h e b e g i n n i n g o f
this sec tion - to show, th at for ~ + ~ [~] and [6] are in equi va-
l e n t . T o p r o v e t h i s w e c o n s i d e r m i n i m a l l e f t i d e a l s o f t h e
g r o u p a l g e b r a C S o f S o v e r C , w h i c h a f f o r d t he r e p r e s e n t a t i o n s
W e k n ow , t h a t t h e s i m p l e t w o - s i d e d i d e a l o f t h e g r o u p a l g e b r a
C G o f a f i n i t e g r o u p G c o n s i s t i n g o f m i n i m a l l e f t i d e a l s a f f o r -
d i n g t h e i r r e d u c i b l e C - r e p r e s e n t a t i o n o f G w i t h c h a r a c t e r C i s
g e n e r a t e d b y t h e c e n t r a l a n d u p t o a n u m e r i c a l f a c t o r i d e m p o t e n t
e l e m e n t
4 . 1 2 D C ( g - 1 ) g •
g E G
I f t h i s i r r e d u c i b l e r e p r e s e n t a t i o n w i t h c h a r a c t e r { i s o n e d i m e n -
s i o n a l, t h e n t h e s i m p l e t w o - s i d e d i d e a l i s a m i n i m a l l e f t i d e a l
itself, since the num ber of the min ima l s1~mmands is equal to the
d i m e n s i o n o f t h e a f f o r d e d i r r e d u c i b l e r e p r e s e n t a t i o n a s i s w e l l
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 71/197
66
k n o w n . I n t h i s c a s e, t h e e l e m e n t 4 . 1 2 i s e v e n a p r i m i t i v e i d e m p o -
t e n t ( u p t o a n u m e r i c a l f a c t o r ) . A p p l y i n g t h i s t o I H ~ an d A V ~ a n d| !
s e t t i n g
4 . 1 3~ ( I " = I ~ ~ . - ~
e p : = ~ I i f p i s a n e v e n / o d d p e r m u t a t i o n , w e o b t a i n :
a a A V ~ i s a f f o r d e d b y C V1 ?r ., 1 4 I H ~ i s a f f o r d e d b y C HI ]( I,
T h e s e e l e m e n t s ~ I a n d ~1 a r e u p t o a n u m e r i c a l f a c t o r p r i m i t i v e
i d e m p o t e n t s o f t h e s u b a l g e b r a s C H ~ a n d C V ~ o f CS . R e g a r d e d a s
e l e m e n t s o f C S t h e y a r e s t i l l i d e m p o t e n t u p t o a n u m e r i c a l f a c t o r
b u t o f c o u r s e i n g e n e r a l n o l o n g e r c e n t r a l e l e m e n t s o r p r i m i t i v e .
T h e l e f t i d e a l s g e n e r a t e d b y a f f o r d t h e i n d u c e d r e p r e s e n t a t i o n s :
4 , ~ ~ t ~ ~ ~ o ~ o ~ ~ c ~ ~ ~ s ~ • ~ ~ ,
- - C H 1
A V ~ ? S i s a f f o r d e d b y C S n~ ~ ~ CSn @ a C V ~ .- - CV I
A n d w e w o u l d l i k e t o s h ow , t h a t t h e p r o d u c t
~ ~ ~e I -= ~(
g e n e r a t e s a m i n i m a l l e f t i d e a l o f C S a f f o r d i n g [ ¢] .
A t f i r s t w e n o t i c e , t h a t b e c a u s e o f H V G V I = { I} t h e c o e f f i c i e n t
o f 1 S n i n e ~ i s I a n d h e n c e
4 . 1 7 e ~ + o
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 72/197
6 7
4 . 5 i m p l i e s , t h a t t h e C - d i m e n s i o n o f ~ C S n ~ r ~ i s I:
4 . 1 8 ¢z =( iC S n 1 = c ) = I
T h e r e f o r e w e o b t a i n w i t h 4 . 1 7 J o h n v o n N e u m a n n ' s l e m m a ( s e e B o e r -
h e r [ 2] , I V, t h e o r e m 2 . 9 ) :
c[ ~ C e ~4. 19 ~1 CSnlrl = "
A p p l y i n g t h i s t o t h e s p e c i a l e l e m e n t ~ 1 ~ I E C S n w e g e t
4 . 2 0 ( e ) 2 = ~ I = e , ~ E C .
I t r e m a i n s t o p r o v e , t h a t t h i s c o m p l e x n u m b e r ~ is u n e q u a l t o
¢ i s p r i m i t i v e .e r o a n d t h a t e
c a n b e e v a l u a t e d b y c a l c u l a t i n g i n t w o w a y s t h e t r a c e o f t h e
l i n e a r t r a n s f o r m a t i o n o f C S n a f f o rd e d b y t h e m u l t i p l i c a t i o n o f
a f r o m t h e r i g h t h a n d s i d e.S n w i t h e
A t f i r s t w e a s s u m e t h e b a s i s o f CS t o b e a d a p t e d t o t h e s u b m o d u l e
C S n e V , i . e . t h a t t h e f i r s t ( ¢ S n e ~ : C ) = : f ~ b a s i s v e c t o r s s p a n
C S n e V . W i t h r e s p e c t t o s u c h a ba s i s t h e m u l t i p l i c a t i o n w i t h e ~
i s d e sc r i b e d b y t h e m a t r i x
o n a c c o u n t o f 4 . 2 0 .
I f on t h e o t h e r h a n d w e c h o o s e t h e e l e m e n t s ~ o f S t o b e t he
b a s i s o f CS n , t h e t r a c e o f th e m u l t i p l i c a t i o n w i t h e ~ i s o b v i o u s -
i n e ~, w h i c h i s I a s w e h a v el y n ! - t i m e s t h e c o e f f i c i e n t o f I S n
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 73/197
68
m e n t i o n e d a b o v e .
0 o m p a r i n g t h i s w i t h 4 .2 1 w e o b t a i n
n! n!
4 . 2 2 ~ = ( C S n e ~ , c ) = ~ .
H e n c e e 1 i s u p t o t h e n u m e r i c a l f a c t o r - 1 = f ~/ n' , a n i d e m p o t e n t
i s e s s e n t i a l l y i d e m p o t e n tleme nt of CS , e I
T o s h o w t h e p r i m i t i v i t y o f e ~ w e n o t i c e , t h a t
s ~ ~ ~ C S n ~ ) ( C S n ~ ~ ).
: C S n ~ 1 ~ I = (. 2 3 C nel _
T h e t w o f a c t o r s o f t h e r i g h t h a n d s i d e o f 4 . 2 3 a r e d i r e c t s u m s o f
m i n i m a l l e f t i d e al s . S i n c e n o n i s o m o r p h i c m i n i m a l l e f t i d e a ls a n -
n i h i l a t e e a c h o t h e r , w e o b t a i n f r o m 4. 4, t h a t t h i s r i g h t h a n d
side of 4.23 is eith er the ideal {0} or a min ima l lef t idea l
w h i c h a f f o r d s [ ~ ].
B e c a u s e o f e V $ 0 t h e l e f t i d e a l C S n e V i s n o t t h e z e r o i d e a l a n d
h e n c e 4 . 1 0 i m p l i e s :
i s a p r i m i t i v e i d e m p o t e n t o f C S a n d t h e m i n i m a lf ~ / n ~ ) e I
a f f o r d s t h e i r r e d u c i b l ee f t i d e a l C S n e V g e n e r a t e d b y e I
C - r e p r e s e n t a t i o n [ ~] o f S .
T o s h o w t h e c o m p l e t e n e s s o f t h i s s y s t e m o f i r r e d u c i b l e o r d i n a r y
r e p r e s e n t a t i o n s C ~S o f S i t t h e r e f o r e s u f f i c e s t o p r o v e t h e
f o l l o w i n g :
4.2 5 ~ ~ ~ ~ CSn e ~ ~ CS e1~ -
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 74/197
6 9
W e s h a l l p r o v e t h i s w i t h t h e a i d o f a l e m m a . B e f o r e s t a t i n g t h i s
l e m m a w e o r d e r th e p a r t i t i on s , d i a g r a m s a n d r e p r e s e n t a t i o n s
a c c o r d i n g t o t h e r o w l e n g t h s m i " W e s a y t h a t m r e s p e c t i v e l y C a]
p r e c e d e s ~ r e s p e c t i v e l y C ~] ( a a n d ~ p a r t i t i o n s o f n ), f o r s h o r t :
C ~] ~ ~ ] , i f th e f i r s t n o n v a n i s h i n g d i f f e r e n c e a i - ~ i i s p o s it i v e .
N o w t h e l e m m a r e a d s a s f o l l o w s :
4 , 2 6 I f [ ~] > [ ~ ] a n d T ~ , T ~ a r e Y o u n g - t a b l e a u x w i t h d i a g r a m s [ a ]
a n d C P~ , t h e n t h e r e a r e a t l e a s t t w o s y m b o l s w h i c h a p p e a r
i n T ~ i n t h e a a m e r o w a n d i n T 6 i n t h e s a m e c o l ~ m ~ .
P r o o f : I f t h i s w e r e n o t t h e e a s e , t h e a s y m b o l s o f t h e f i r s t
r o w o f T w o u l d a p p e a r i n d i f f e r e n t c o l u m n s o f T 6 s o t h a t
6 1 ~ a 1 . S i n c e a > 6 t h i s i m p l i e s ~ I = 6 1 "
A v e r t i c a l p e r m u t a t i o n - w h i c h d o e s n ' t d i s t u r b t h e d i s t r i b u t i o n
o f t h e s y m b o l s i n t h e c o l u m n s o f T 6 - t r a n s f e r s t h e s e ~I s y m b o l s
t o t h e p l a c e s o f t h e f i r s t r o w o f T 6 . D i s r e g a r d i n g t h i s n e w f i r s t
r o w a n d u s i n g t h e s a m e a r g u m e n t a s a b o v e w e g e t a = ~ 2 a n d s o
o n, a r r i v i n g f i n a l l y a t ~ = 6 w h i c h i s a c o n t r a d i c t i o n t o t h e
a s s u m p t i o n ~ > ~.
q . e . d .
P r o 9 f o f 4 . 2 ~ : I f ~ ~ 6 w e c a n a s s u m e w i t h o u t r e s t r i c t i o n t h a t
I f ~ E S , 4 . 2 6 i m p l i e s t h a t i n
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 75/197
7 O
I )~ T ~ - -m o o o I ~ I o o m a o l o
t h e r e a r e t w o s y m b o l s , s a y s a n d t , a p p e a r i n g i n t h e s am e r o w o f
~ T~ a nd i n t h e s a m e c o lu m n o f T I~ . T h e i r t r a n s p o s i t i o n ( s t ) b e l o n g s
t o ~ j ~ - 1 , t h e g r o u p o f t h e h o r i z o n t a l p e r m u t a t i o n s o f ~ T ~ a s w e l l
as to VI~. Th us
( s t ) ~ -1 = ~ - I , , 1 ~ ( s t ) = _ , i~ ,
f r o m w h a t f o l l o ws , t h a t
e 1 ~ e ~ - I = - e1 ~( st )~ eV ~ - I = - e 1 ~ e ~ - I .
e 1 ~ e ~ - I = O , V ~ E S n , ~ e 1 ~ e ~ = 0 , V ~ E S n , ~ e 1~ xe ~ = O , V x E C S n .
A n d i t i s w e l l k n o w n , t h a t t h i s i m p l i e s t h e s t a t e m e n t ( cf . B o e r n e r
[ 2 ], I I I, t h e o r e m 3 . 8 ) .
q . e . d .
W e s ! i m m ~ r i z e , w h a t w e h a v e p r o v e d :
T h e r e p r e s e n t a t i o n s [ a] d e f i n e d b y 4 . 6 f o r m a c o m p l e t e
s y s t e m
[ [ ~ ] : = I S ~ $ S n N A S ~ , ~ S n I a p a r t i t i o n o f n ]
o f p a i r w i s e i n e q u i v a l e n t a n d i r r e d u c i b l e C - r e p r e s e n t a t i o n s
of S n.
T h u s w e h a v e c o m p l e t e d t h e f i r s t s t e p t o w a r d s a n e x p l i c i t d e -
s c r i p t i o n o f t he o r d i n a r y i r r e d u c i b l e r e p r e s e n t a t i o n s o f S .
T h e r e p r e s e n t i n g m a t r i c e s t h e m s e l v e s w e r e g i v e n b y A . Y o u n g
( Y o u n g [ 2] ), w e s h a l l d e s c r i b e t h e d e r i v a t i o n i n d e t a i l i n a
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 76/197
7 1
f o l l o w i n g p a r t . H e r e w e s h a l l o n l y s k e t c h t h e n e x t s t e p s b r i e f -
ly.
W e r e t u r n t o th e d e f i n i t i o n 4 . 1 6 o f t h e g e n e r a t i n g p r i m i t i v e i d e m -
5p o t e n t s . T o d e fi n e e w e h a v e u s e d o n l y t h e f i r s t Y o u n g - t a b l e a u
TIm w i t h Y o u m g - d i a g r a m [ ~] . T h e e l e m e n t
e I = ~i~1
a n d V ~ o f t h e h o r i z o n t a lc o n s t r u c t e d w i t h t h e a i d o f t h e g r o u p s H I
a g e n e r a t e s a m i n i m a l l e f t i d e a l o u ta n d v e r t i c a l p e r m u t a t i o n s o f T I
o f t h e s i m p l e t w o - s i d e d i d e a l i n C S t o w h i c h t h e i r r e d u c i b l e o r -
d i n a r y r e p r e s e n t a t i o n [ 51 c o r r es p o n ds .
T h i s s i m p l e t w o - s i d e d i d e a l i s a d i r e c t s u m o f f a = ( CS n e ~ : C )
m i n i m a l l e f t i d e a l s w h i c h a r e i s o m o r p h i c t o £ S n e ~ . T h u s w e
a s k f o r e l e m e n t s g e n e r a t i n g t h e r e m a i n i n g m i n i m a l l e f t i d e a l s
o u t o f t h i s s i m p l e t w o - s i d e d i d e al .
P r e s u m a b l y s o m e o f t h e e l e m e n t s
e := ~i~ i
5c o n s t r u c t e d a n a l o g o u s l y t o e b u t w i t h t h e a i d o f o t h e r t a b l e a u x
aT i g e n e r a t e t h e s e l e f t i d e a l s .
T h i s i s a c t u a l l y t h e c a s e ( t h a t C S n e ~ ~ C S n e ~ i s t r i v i a l b y d e -
f i n i t i o n o f [ 5] ). O b v i o u s l y t h e r e a r e n ! d i f f e r e n t t a h l e a u x w i t h
Y o u n g - d i a g r a m [ 5] , n a m e l y t h e t a b l e a u x ~ T I , ~ E S . W e p i c k o u t
s o m e o f t h e m, t h e s o - c a l l e d s t a n d a r d - t a b l e a u ~ , c h a r a c t e r i z e d b y
t h e p r o p e r t y , t h a t i n s u c h a t a b l e a u t h e s y m b o l s i n e a c h r o w a n d
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 77/197
72
i n e a c h c o l n m n a r e i n i n c r e a s i n g o r d e r , i .e . t h a t t h e s y m b o l i n
t h e p o s i t i o n ( i ,j ) ( i - t h r o w , j - t h c o l n m n ) p r e c e d e s t h a t i n t h e
( k , 1 ) - p o s i t i o n i f i <_ k a n d j ~ l. E . g .
1 2 3 1 2 4 1 2 5 1 3 4 1 3 5
4 5 3 5 3 4 2 5 2 4
a r e a ll t h e s t a n d a r d - t a b l e a u x w i t h Y o u n g - d i a g r a m [ 3, 2] .
L e t u s d e n o te b y f ~ th e n u m b e r o f s t a n d a r d - t a b l e a u x w i t h Y o u n g -
d i a g r a m [ a ]. I t w i l l a p p e a r , t h a t f a = f a = ( C S n e ? : £ ) .
W e a r r a n g e t h e s t a n d a r d - t a b l e a u x T i i n d i c t i o n a r y o r d e r, i .e .
i <j i f t h e f i r s t n o n v a n i s h i n g d i f f e r e n c e o f s y m b o l s l o c a t e d a t
~ ( c o m p a r i n g t h e s y m b o l s i n a r o w f r o mh e s a m e p l a c e i n T i a n d Tj
t h e l e f t to th e r i g h t a n d t h e r o w s d o w n w a r d s ) i s n e g a t i v e . T h e
a b o v e a r r a n g e m e n t o f t h e s t a n d a r d t a b l e a u x w i t h d i a g r a m [ 3 ,2 ]
p r o v i d e s a n e x a m p l e o f t h i s o r d e r i n g .
b e t h e g r o u p s o f t h e h o r i z o n t a l p e r m u t a t i o n s a n d ofe t H ~ a n d V i
t h e v e r t i c a l p e r m u t a t i o n s o f T ~ , l e t
~ .=4 . 2 8 E i : = ~ ' ~ ' ~ i
~ E H i
a n d
4 . 2 9
p E V i
: = ~ ~ a ~ ~ p ~ p , 1 ~ i < _ f ~ .
e ~ i ~ i = ~ E H i , P E ~ i
W e w o u l d l i k e t o s h o w , t h a t
4 . 3 0 ~ C S n e ~~ , i
i s a d i r e c t s u m a n d e q u a l t o C S . T h i s w o u l d i m p l y f ~ = f ~ a n d
t h a t $ C S n e ; i s t h e s i m p l e t w o - s i d e d i d e a l o f C Sn , w h o s e s 1~ m ma nd s
i
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 78/197
73
C S n e ~ a f f o r d [ a ].
T h e f i r s t s t e p t o w a r d s a p r o o f o f 4 . 3 0 i s t he p r o o f o f
a
4.~I i < j ~ ej e i = O.
A n d t h i s w i l l b e s h o w n w i t h t h e a i d o f t h e f o l l o w i n g l e m m a :
I f i< j , t h e n t h e r e a r e a t l e a s t t w o s y m b o l s a p p e a r i n g i n t h e
s a m e r o w o f T i a n d i n t h e s a m e c o l u m n o f T .
P r o o f : L e t ( k , 1) b e t h e p l a c e o f t h e f i r s t n o d e o f [ a ] r e p l a c e d
a i < j i m p l i e sy d i f f e r e n t s y m b o l s , s a y b y s r e s p . t i n T i r e s p . T j .
s < t . W e a s k f o r t h e p l a c e ( m , o ) , w h e r e s a p p e a r s i n T ~ .
O n a c c o u n t o f t h e s t a n d a r d n e s s o f T ~ , t p r e c e d e s a l l t h e s y m b o l s
l o c a t e d a t p l a c e s ( p , q) w i t h p _ ~ k a n d q ~ l . S i n c e ( k ,1 ) i s t h e f i r s t
p l a c e o c c u p i e d b y d i f f e r e n t s y m b o l s , t h i s i m p l i e s m > k , o < l . T h u s
t h e p l a c e ( k , o ) i s o c c u p i e d b y t h e s a m e s y m b o l , s a y b y r , i n T .l
a s w e l l a s i n T ~. H e n c e r a n d s f u l f i l t h e s t a t e m e n t .
q . e . d .
D e n o t i n g b y r a n d s t w o s y m b o l s a p p e a r i n g i n t he s a m e r o w o f T i
a n d i n t h e s a m e c o l u m n o f T~., w e h a v e f o r t h e i r t r a n s p o s i t i o n
(rs) :
a ~ a -e~ (rs ) ~ a ~ ~ ~ 0rs) E Hi nV j ~ eje i = e = -ej e i ~ eje i = •
T h i s p r o v e s 4 . 3 1 .
T o p r o c e e d w i t h t h e p r o o f o f t h a t 4 . 3 0 i s a d i r e c t s u m a n d e q u a l
t o C Sn , w e c o n s i d e r a n e q u a t i o n
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 79/197
?4
a
a e = 0x l e I + . . . + x f a
( x i E C S n ) . I f w e m u l t i p l y b y e f r o m t h e r i g h t h a n d s i d e , s i n c e
4 . 3 1 i s v a l i d , w e o b t a i n ~ x l e ~ = O , h e n c e x l e ~ = O . T h e n w e m u l -
a a n d g e ti p l y b y e x 2 e 2 = 0 a n d s o o n . T h i s p r o v e s , t h a t t h e
s u m 4 . 3 0 i s a d i r e c t s u m .
A c o m b i n a t o r i a l c o n s i d e r a t i o n ( s e e B o e r n e r [ 2] , I V , ~ 7 ) s h o w s t h a t
4 . 3 3 Z ( f ~ ) 2 = n ! .
a
S i n c e 4 . 3 0 i s a d i r e c t s u m w e h a v e f u _> f ~, t o g e t h e r w i t h 4 . 3 3 w e
c o n c l u d e , t h a t f ~ = f a a n d t h i s c o m p l e t e s t h e p r o o f , s o t h a t t h e
f o l l o w i n g i s v a l i d :
¢.34
f ~
C S n = • • £ S n e ~ .
a i = I
H e n c e
f ~
4 . 3 5 ~ C S n e ~i = 1
i s t h e t w o - s i d e d i d e a l t o w h i c h [ ~] b e l o n g s .
T h e t h e o r e m o f W e d d e r b u r n s a y s : ~ C S n e ~ is i s o m o r p h i c t o t h e r i n g
i
o f ( f a x f a ) - m a t r i c e s o v e r C . H e n c e a l l w h a t r e m a i n s t o c o n s t r u c t r e -
p r e s e n t i n g m a t r i c e s t h e m s e l v e s i s t o f i n d a b a s i s o f e l e m e n t s
e ik ~ o f ~ C S n e ~ s a t i s f y i n gi
4 . 3 6 e ~i j e k l = G j k e i l
( G j k t h e K r o n e c k e r - s y m b o l : G j k = O i f j Sk , =I , i f j = k) .
T h u s t h e m a t r i c e s ( d ~ k ( ~ )) b u i l t f r o m t h e c o e f f i c i e n t s o f
f ~
4 . 3 7 ~ = ~ d " " e ~i k t ~ ; i k
i , k = 1
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 80/197
75
a r e t h e e l e m e n t s o f ~ aS . P o r t h i s t h e r e a d e r i s r e f e r r e d t o B o e r -
n o r C IS , C 2S . C o r r e s p o n d i n g t o t h r e e w a y s o f c h o o s i n g t h e b a s i s
e l e m e n t s e i k t h e r e a r e t h r ee f o r m s o f t h e r e p r e s e n t i n g m a t r i c e s :
Y o u n ~ ' s n a t u r a l f o r m ( d ~ k E Z ) , Y o u n g ' s s e m i n o r m a l f o r m ( d i k E Q )
a n d Y o u n g ' s c r t h o g o n a l f o r m ( d ~ k E R, t h e m a t r i c e s a r e o r t h o g o n a l ) .
T h e n a t u r a l f o r m i s d e r i v e d i n B o e r n e r ~ IS , t h e o r t h o g o n a l a n d
s e m i n o r m a l fo r m i n B o o m e r E 2S . w e s h a l l d e s c ri b e t h e se m i n o r m a l
f o r m n o w .
T o g e t t h e m a t r i c e s r e p r e s e n t i n g e l e m e n t s o f t h e s u b g r o u p S n _ I
S ( c o n s i s t i n g o f th e p e r m u t a t i o n s f i x i n g t h e s y m b o l n E ~ ) i n
r e d u c e d f o r m , i .e . w i t h t h e m a t r i c e s o f th e i r r e d u c i b l e c o n s t i -
t u e n t s a l o n g t h e m a i n d i a g o n a l a n d z e r o s e l s e w h e r e , w e c h o o s e a n
o r d e r i n g o f t h e s t a n d a r d - t a b l e a u x w i t h r e s p e c t t o t h is s y m b o l n :
f ~I T ~ o f t h e s t a n d a r d -o o b t a i n t h e l a s t l e t t e r s e q u e n c e T ~ , . .. ,
t a b l e a u x w i t h Y o u n g - d i a g r a m ~ S , w e t a k e a t f i r s t t he s t a n d a r d -
t a b l e a u x c o n t a i n i n g n i n t h e l a st r ow , t h e n t h e s t a n d a r d - t a b l e a u x
c o n t a i n i n g n i n t h e l a s t b u t o n e r o w a n d s o o n. T h e n w e o r d e r t h e
s t a n d a r d - t a b l e a u x c o n t a i n i n g n i n t he s a m e r o w w i t h r e s p e c t t o
n-S and so on. E.g.
4. 38 I 2 3 I 2 4 133 4 I 2 5 I 3 5
4 5 3 5 2 5 3 4 2 4
i s t h e l a s t l e t t e r s e q u e n c e o f t h e s t a n d a r d - t a b l e a u x w i t h Y o u n g -
d i a g r a m E 3 ,2 ~ . T o d i s t i n g u i s h b e t w e e n t h e l a s t l e t t e r s e q u e n c e
i m a ya n d t h e d i c t i o n a r y o r d e r i n g w e h a v e e x c h a n g e d t h e i n d ic e s : T ~
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 81/197
76
b e d i f f e r e n t f r o m T i -
B e f o r e w e c a n f o r m u l a t e t h e t h e o r e m w e h a v e t o i n t r o d u c e t h e a x i a l
i id i s t a n c e d ~ ( r , s ) o f t w o s y m b o l s r a n d s in T ~ : i f r is l o c a t e d a t
( i r , J r ) a n d s a t ( i s , J s ) , w e d e f i n e :
i4 . 3 9 d ~ ( r , s ) : = ( j r - J s ) + ( i s - i r ) .
d ~ ( r , s ) i s t h e n u m b e r o f s t e p s w e n e e d t o c o m e f r o m r t o s ,h u s
i f s t e p s t o t h e l e f t a n d d o w n w a r d s a r e c o u n t e d p o s i t i v e l y a n d
s t e p s t o t h e r i g h t a n d u p w a r d s a r e c o u n t e d n e g a t i v e l y .
N o w t h e t h e o r e m d e s c r i b i n g Y o u n g ' s s e m i n o r m a l f o r m o f [m ] r e a d s
a s f o l l o w s :
I fm4 . 4 0 I f T a, . . . , T ~ i s t h e l a s t l e t t e r s e q u e n c e o f t h e s t a n d a r d -
t a b l e a u x w i t h Y o u n g - d i a g r a m [ ~ ] , t h e n f r o m t h e m a t r i c e s
( d ~ k ( t , t + 1 ) ) r e p r e s e n t i n g t h e t r a n s p o s i t i o n s ( t , t+ 1 )
( l ~t <_ n -1 ) c a n b e b u i l t a r e p r e s e n t a t i o n e q u i v a l e n t t o [ ~ ]
i f w e s e t
~ i ( t , t + l ii ) d ) : = ! 1 , i f T ~ c o n t a i n s t a n d t +1 i n t h e s a m e
r o w / c o l ~ m n ,
( i i ) a n d f o r t h e s u b m a t r i x
d ~ i ( t , t + 1 ) d i j ( t , t + l d a ( , ~ + I ) - 1
k ~ : =d ~ i ( t , t + 1 ) d j j ( t , t + 1 I
if T a = (t,t+ 1)T and i<j,
( i i i ) d ~ j ( t , t + 1 ) : = 0 f o r a l l t h e o t h e r e n t r i e s .
11 - d i ( t , t + l ) -2 ~
JI
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 82/197
77
L a t e r o n w e s h a l l u s e t h i s t h e o r e m f o r t h e e v a l u a t i o n o f
e x a m p l e s o f r e p r e s e n t a t i o n s o f w r e a t h p r o d u c t s . P o r t h is w e s h a l l
a l s o u s e s om e r e s u l t s a b o u t t h e o r d i n a r y i r r e d u c i b l e c h a r a c t e r s
o f t h e s y m m e t r i c g r o u p w h i c h w e s n m m a r i z e n o w .
A to o l o f g r e a t u t i l i t y i s t h e t h e o r e m , t h a t t h e c h a r a c t e r C o f
[ a] c a n b e w r i t t e n i n t h e d e t e r m i n a n t a l f o r m
a s a l i n e a r c o m b i n a t i o n ( w i t h r a t i o n a l i n t e g r a l c o e f f i c i e n t s ) o f
c h a r a c t e r s i n d u c e d b y i d e n t i t y r e p r e s e n t a t i o n s o f Y o u n g s u b g r o u p s .
4 . 41 h a s t o b e u n d e r s t o o d a s f o l l o w s :
~ [ ~ i + ~ ( i ) - i ]4 . 4 2 ~ = ~ e ~ X ,
~ E S h
~ [ ~ i ]i f X d e n o t e s t h e c h a r a c t e r o f -- [ ~ i ] ( s e e 4 . 9 ) , i f ~ i ~ O , V i ,
~ [ ~ i ]a n d i f w e s e t X = O , i f o n e ~ i < O , a n d i f w e s e t i n t h e d e t e r -
m i n a n t a l e x p r e s s i o n 4 . 41 :
F o r e x a m p l e
[ 3 ]
[ 3 , 1 2 ] = t
0
[ 4 ] [ 5 ]
[ 1 ] [ 2 ]
w h a t m e a n s , t h a t
[ 0 ] : = 1 , [ m ] .- '- O , i f m < O
= [ 3 ] [ ~ ] [ , ] - [ 3 ] [ 2 ] - [ 4 ] [ ~ ] + [ 5 ] ,
c ( 3 , 1 2 ) = x [ 3 ] [ 1 ] [ ~ ] _ x [ 3 ] [ 2 ] _ x [ 4 3 1 1 ] + x [ 5 ]
A b o v e a l l i t i s r e m a r k a b l e , t h a t 4 . 41 l i k e 4 . 4 c a n b e p r o v e d u s i n g
t h e r e s u l t s a b o u t d o u b l e c o s e t s m e n t i o n e d i n s e c t i o n I a n d M a c k e y ' s
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 83/197
78
intert wining numbe r theo rem (see Coleman [1] , of. also ettudGzalp
[ I ] ) so t h a t w e c a n g e t a h o m o g e n e o u s a n d l u c i d d e r i v a t i o n o f
t h e s e f u n d a m e n t a l a n d c l a s s i c a l r e s u l t s f o l l o w i n g G o l e m a n ' s h i n t
to use Mackey' s theorem.
A co rollar y of 4.41 is
C~ (~ ) = { (-1)r'o elsewhereif~]=[n-r,lr],o<r<_n-1.
~or the only You ng subgroup contain ing n-cycle s is S itself.
H e n c e a n n - c y c l e ~ h a s a n o n v a n i s h i n g c h a r a c t e r v a l u e C ~ ( ~) a t
most when [n] occurs in the deter minant al expressio n 4.41, and
this is obv ious ly the case only if [~] is of the for m [n-r,lr].
In this case we have
fin-r] [n-r+1] ... In -l ] In]
[ n -r 's r ] = I . . i . .. . ! ] ! . . . i ~ i . ! ~ ] ! . ! ~ !
I 0 0 . . . I1 ]
( 1 ) r [ n ] + . . . . . , . . . . . . . . . . . . ,
eaoh s~mm~na ~ In ]
hence 4.42 is valid.
To prove 4.41 we introduce the concept of a hook, whose impor-
tance was fir st noted by T. Nakayam a (Nakayama [1]).
v~ith the aid of this concept a very simple recurs ion formul a for
~a can be for mulated and a very simple equ ation for f~ can be
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 84/197
7 9
g i v e n .
A h o o k w e c a l l e a c h F - s h a p e d a r r a n g e m e n t H ~ j o f n o d e s o u t o f a
Y o u n g - d i a g r a m [ ~] w h i c h c o n s i s t s o f t h e ( i , j ) - n o d e , t h e c o r n e r o f
t h e h o o k , a s w e l l a s o f t h e ( i , k ) - n o d e s , k > J , w h i c h f o r m t h e a r m
o f t h e h o o k , a n d t h e ( l , j ) - n o d e s , l > i , w h i c h f o r m t h e l e g o f t h e
h o o k H ~ j. ~ T h e ( i , a i ) - n o d e i s c a l l e d t h e h a n d o f t h e h o o k , t h e
.... H ~ .a ~ , j ) - n o d e i s c a l l e d t h e f o o t of i j "
: /
H i j
c o r n e r h a n d
. J . . . . . /
• I a r mi leg
, f o o t
T h e n u m b e r
4.43 hij := ~i - j + ~j - i + 1
o f n o d e s t h e h o o k H ~ j c o n s i s t s o f i s c a l l e d t h e ~ o f t h e
h o o k . T h e n u m b e r
aI i " = e ~ - i. 44 j •
i s c a l l e d t h e l e g - l e n g t h o f H i j .
a of the rim of [u]o H i j c o r r e s p o n d s t h e p a r t o f l e n g t h h aij
the han d and the arm of H~j~ in-o n s i s t i n g o f t h e n o d e s b e t w e e n
c l u s i v e . E . g .- @ ®
@ ®
®
@
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 85/197
8 0
w h e r e t h e e n c i r c l e d n o d e s i n d i c a t e t h e p a r t o f t h e r i m w h i c h c o r -
res pon ds to the ho ok H(3'2'12)11 ~ [3'2' 12]"
T h i s a s s o c i a t e d R a r t o f t h e r i m w i l l b e d e n o t e d b y
R i j •
A n d i t i s i m p o r t a n t , t h a t t h e r e s u l t [ ~ ] \R ~ j o f r e m o v i n g R ~ j f r o m
[ a] i s a Y o u n g - d i a g r a m a g a i n o r e q u a l t o [ 0 ] ( w h a t i s s o m e t i m e s
c a l l e d t h e z e r o - d i a 6 r a m ) . E . g .
• i J ~ J
[ 3 , 2 , 1 2 ] \ R 1 3 ' 2 ' 1 2 ) - / f =1 ]1 = " "
/
/
U s i n g t h i s n o t a t i o n w e c a n f o r m u l a t ~ t h e f o l l o w i n g t w o v e r y i m p o r -
t a n t f o r m u l a e :
~ . 4 5 ( " M u r n a g h a n - N a k a y a m a - f o r m u l a " )
If ~ £ S is of type T~ = (al, ... ,a n) so that a ~ 0, and
~ * E S n _ k i s o f t y p e T ~ * = ( a l , . . . , a k _ 1 , a k - S , a k + 1 , . . . , a n ) ,
t h e n
C ~ ( ~) i , j : h i j = k
if we set C [0] .= I~
T h i s i s t h e r e c u r s i o n f o r m u l a f o r t h e o r d i n a r y i r r e d u c i b l e
c h a r a c t e r s o f S . T h e f o r m u l a f o r t h e d i m e n s i o n o f [ ~ ] w e o w e
t o F r a m e , R o b i n s o n a n d T h r a l l ( F r a m e / R o b i n s o n / T h r a l l [ I] ), a nd
i t i s o f f a s c i n a t i n g s i m p l i c i t y :
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 86/197
81
$ . $ 6 T h e d i m e n s i o n o f [ ~ i s t h e q u o t i e n t o f n ! an d t h e p r o d u c t
o f a l l t h e h o o k - l e n g t h s :
= !n . l. T h i j -i , j
4.45 implies, that C~(~) = O if ~ conta ins a k-cycle but [a~ con-
t a i n s n o k -h o o k , a n d i t i m p l i e s 4 . 4 2 .
I t s h o u l d b e o b s e r v e d , t h a t t h e o r d e r o f r e m o v i n g t w o p a r t s o f
t h e r i m a s s o c i a t e d w i t h h o o k s i s i m m a t e r i a l , t h e r e s u l t i n g d i a -
g r a m w i l l b e t h e s a m e i n b o t h c a s es .
N o w w e h a v e m e n t i o n e d t h e m o s t i m p o r t a n t r e s u l t s a b o u t t h e o r d i -
n a r y i r r e d u c i b l e r e p r e s e n t a t i o n s . C e r t a i n a n a l o g u e s c o n c e r n i n g r e-
d u c i b l e r e p r e s e n t a t i o n s c a n b e f o r m u l a t ed , w h i c h w i l l b e o f u s e
later on.
W e c o n s i d e r t h e r e p r e s e n t a t i o n s
[ ~ an i r reduc ib le rep resen ta t i on o f Sm, [~ an i r r edu cib le re-
p resen ta t i on o f Sn-
T h e r e i s a n a n a l o g u e t o 4 . 4 0 w h i c h d e s c r i b e s t h e r e p r e s e n t i n g m a -
t ri c es of C ~ .
T o f o r m u l a t e t h i s w e h a v e t o g e n e r a l i z e t h e n o t a t i o n o f t h e Y o u n g -
d i a g r a m . T o d o t h i s w e c o n s i d e r a d i a g r a m ~ a n d a d i a g r a m ~
w h i c h c a n b e s u p e r i m p o s e d u p o n C mS , u p p e r l e f t h a n d c o r n e r u p o n
u p p e r l e f t h a n d c o r n e r s u c h t h a t ~ i s c o n t a i n e d e n t i r e l y w i t h i n
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 87/197
82
m .
T h e r e s i d u u m o f [ a ] n o t c o v e r e d b y l i B ] i s c a l l e d a s k e w - d i a g r a m
a n d d e n o t e d b y
E . g .
[ a ] - [ p ] .
[ v , 6 , 3 , 1 ] - [ ' z , 2 , 1 ] =
= [ 6 , 3 , 1 ] - [ 2 , 1 ]
( [ a ] - [ ~ ] i s b y n o m e a n s u n i q u e l y d e t e r m i n e d i n t e r m s o f [ a ] a n d
[ p ] ) .
S p e c i a l c a s e s o f s k e w d i a g r a m s c o n s i s t o f t w o d i s j o i n t d i a g r a m s :
C ~ P ] " = -
E . g .
[ 4 , 3 , 2 , 1 ] - [ 2 2 ] = [ 2 , 1 1 2 , 1 ] = "
W e s h a l l c o n s i d e r o n l y t h e s e s p e c i a l c a s e s o f s k e w d i a g r a m s .
iT a b l e a u x a n d s t a n d a r d - t a b l e a u x T a ; ~ a r e d e f i n ed a s b e f o re •
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 88/197
83
The number of standard-tableaux with Young-di agram [a; ~] is ob-
v i o u s l y
4 4 8 : ,
i.e . equal to the dimension of [a] [~] . The theore m analogous to
4.40 reads as follows (Robinson [5], 3.1):
1 fa;~..,T ^ (f~;~:=(m+n)!faf~/m!n!) is the last lette r4.49 If Tail,. a;p . . . . . .
sequence of the standard-tableaux wit h skew diag ram [~;~],
then we can buil d a representation equivalent to [~][~],
if we take for the entries of the matric es (d-'~(t,t+1))
repre senti ng the transpositions (t,t+1):
(i) d~l~(t,t+ 1 ) = ~I, if t and t+1 occur in the same rbw/
icolumn of T~;~,
(i i) [ d ~ ~(t 't+ 1) ~ijaa;(t 't +1 1~ . Id i~; (t,t+1)-I 1-d~;( t , t + 1 ) - ~ iI
[ d ~ ( t , t + 1 ) d ~ ( t , t + 1 1 d ~; ~( t, t+ 1) J
or := [ ~ 2 ]
Tf t and t+1 occur in ~;~ in the same diagr am consti-
tuent or not.
( i i i ) d ~ ( t , t + 1 ) = 0 f o r a l l t h e o t he r e nt r ie s .!
The formula analogous to the Murnaghan- Nakayama-for mula reads as
foll ows (Osi ma [I ]) :
4.50 If ~ E Sm+ is of type T~ = (al,...,am+ n) with a ~ 0 and if
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 89/197
84
~ * E S m + n _ i s o f t y p e T ~ * = ( a l , . . . , a k _ 1 , a k - l , a k + 1 , . . . , a m + n ) ,
t h e n w e h a v e f o r t h e v a l u e X ~ ; ~ ( ~ ) o f t he c h a r a c t e r o f [ ~ ] [ ~]
o n ~
= (
i , j :hi~=k
if we set X [O] := I.
-1) l~ X
T h e f o l l o w i n g t h e o r e m ( s t a te d b y L i t t l e w o o d a n d R i c h a r d s o n a n d
p r o v e d f i r s t b y R o b i n s o n ) d e s c r i b es , h o w w e c a n ge t t h e i r r e d u c i b l e
c o n s t i t u e n t s o f [ ~ ][ ~ ] :
4 .5 1 ( " L i t t l e w o o d - R i c h a r d s o n - r u l e " )
T h e i r r e d u c i b l e c o n s t i t u e n t s o f [ ~ ] [ ~ ] a r e e x a c t l y t h e r e p r e -
s e n t a t i o n s [ y] o f S m + n , w h o s e d i a g r a m s a r i s e b y a d d i n g t h e
n o d e s o f [ ~] to [ ~ ] a c c o r d i n g t o t he f o l l o w i n g r u l e s :
( i) T o [ ~ ] a d d t h e n o d e s o f t h e f i r s t r o w o f [ ~] . T h e s e m a y
b e a d d e d t o o n e r o w o r d i v i d e d i n t o s u b s e t s p r e s e r v i n g
t h e i r o r d e r a n d a d d e d t o d i f f e r e n t r o w s , t h e f i r s t s u b s e t
t o o n e r o w o f [ ~ ] , t h e s e c o n d t o a s u b s e q u e n t r o w , t h e
t h i r d t o a s u b s e q u e n t t o t h i s a n d s o o n . A f t e r t h e
a d d i t i o n s t h e r e s u l t i n g d i a g r a m m a y n o t c o n t a i n t w o a dd e d
n o d e s i n t h e s a m e c o l u m n .
( i i ) N e x t a d d t h e s e c o n d r o w o f [ ~ ] a c c o r d i n g t o t h e s a m e
r u l e s f o l l o w e d b y t h e r e m a i n i n g r o w s i n s u c c e s s i o n a n d
s u c h t h a t e a c h n o d e o f [ ~] a p p e a r s i n a l a t e r r o w o f
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 90/197
8 5
t h e c o m p o u n d d i a g r a m [¥] t h a n t h a t n o d e i m m e d i a t e l y
above it in IriS.
A s p e c i a l a n d v e r y i m p o r t a n t c a s e i s t h e b r a n c h i n g t h e o r e m f o r t h e
i r r e d u c i b l e o d i n a r 2 r e p r e s e n t a t i o n s o f S n :
4 . 5 2 [ ~ ] ~ S n _ I i ' j : h i J = 1
I t i s e a s i l y t o p r o v e t h i s u s i n g 4 . 51 a n d t h e r e c i p r o c i t y t h e o r e m
o f ~ r o b e n i u s . P o r 4 . 5 1 s a y s , t h a t t h e c o n s t i t u e n t s o f [ ~ ] $ S n + I
= [ ~ ] [ I] a r e e x a c t l y t h e r e p r e s e n t a t i o n s [ ¥] o f S n + 1 , w h o s e d i a -
g r a m s a r i s e b y a d d i n g a n o d e t o [ ~] . T h u s b y F r o b e n i u s ' r e c i p r o -
c i t y t h e o r e m t h e d i a g r a m s o f t h e c o n s t i t u e n t s o f [ ~] ~ S n _ I a r i s e
b y s u b t r a c t i n g a n o d e i n a l l t h e p o s s i b l e w a y s .
C o n c l u d i n g t h i s s e c t i o n w e w o u l d l i k e t o c o n s i d e r t h e c o n n e c t i o n
b e t w e e n t he i r r e d u c i b l e C - r e p r e s e n t a t i o n s o f S a n d A n .
A f i r s t r e m a r k f o l l o w s i m m e d i a t e l y f r o m 4 . 11 :
4 . 5 3 [ ~ 2 ~ A ~ ~ [ ~ ' 2 ~ A n •
T h u s [ ~] a n d [ a ' ] a r e a s s o c i a t e d r e p r e s e n t a t i o n s in t he s e n s e o f
C l i f f o r d ' s t h e o r y o f r e p r e s e n t a t i o n s o f g r o u p s w i t h n o r m a l d i v i -
s o r s ( C l i f f o r d [ 1] , c f. a l s o B o e r n e r [ 2 ] , I I I , ~ 13 ). B u t f r o m
C l i f f o r d ' s t h e o r y w e g e t m u c h m o r e :
4.5 4 (i) a + ~' ~ [~] ~ A = [~'] ~ A is irr edu cib le.
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 91/197
8 6
( i i ) a = ~' ~ ( [ a ] = [ a ' ] ) ~ A n = [ ~ ] + + [ a ] - w i t h t w o i r r e d u -
o i b l e a n d c o n j u g a t e r e p r e s e n t a t i o n s [ ~ o f A n ( i .e .
[ ~ ] + ( a ) i s e q u i v a l e n t t o [ m ] - , V a E S , i f
[ ~ ] + ( a ) ( a ~ a - 1 ) : = [ ~ ] + ( ~ ) , v ~ e A n ) .
H e n c e f o r t h e c h a r a c t e r s w e m a y u s e t h e M u r n a g h a n - N a k a y a m a - f o r m u l a
a g a i n i n t h e c a s e ~ ~ ~ ' . I f ~ = ~' d i f f i c u l t i e s a r i s e a l s o b e -
c a u s e o f t h e s p l i t t i n g o f t he S n - c l a s s e s . B u t w e h a v e ( s e e B o e r n e r
[ 2] ) a r e s u l t o f F r o b e n i u s :
( " F r o b e n i u s ' t h e o r e m " )
I f a = a' t h e c l a s s w i t h t h e p a r t i t i o n
: = ( h ~ 1 , h 2 2 , . . . , h k k )
i s a s p l i t t i n g S n - o l a s s C ~ = O ~ + U C ~ -. O n t h i s c l a s s C h a s
t h e v a l u e
C~ = ( - 1 ) ( n - k ) / 2 ,
a nd t h e v a l u e s o f Ce ~ o n C~ a r e
4 V~ r,= _ h i i )p + ~ ( C ~ + p
i f w e d e n o t e t h e i r r e d u c i b l e c o n s t i t u e n t s o f [ ~] ~ A n i n t h i s
w a y . O n a l l t h e o t h e r c l a s s e s w i t h p a r t i t i o n s V $ ~, w e h a v e
5 +¢_ = ~ / 2 .
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 92/197
87
W e r e c a l l t h e c o n s i d e r a t i o n s o f th e f i r st s e c t i o n c o n c e r n i n g t h e
a m b i v a l e n c y o f a l t e r n a t i n g g r o u p s ( cf . 1 . 2 5 ) a n d t a k e i n t o a c c o u n t ,
t h a t t h e a m b i v a l e n c y o f a g r o u p i s e q u i v a l e n t t o t h e r e a l i t y o f i t s
o r d i n a r y i r r e d u c i b l e c h a r a c t e r s . H e n c e t h e t a b l e s o f A I = A 2 = ( I ] ,
A 5 , A 6, A I O a n d A 1 4 a r e t h e o n l y c h a r a c t e r t a b l e s o f a l t e r n a t i n g
g r o u p s c o n t a i n i n g o n l y r e a l e n t r i e s , w h i l e e . g .
A 3 (3,0,0) (0,0,1) + (0,0 ,1)-
1 1 1
1 ( - 1 - q g ) / 2
1 ( 1 - i ~ ) / 2 ( 1 + i ~ ) / 2
[ 3 ]
[ 2 , 1 ] +
[ 2 , 1 ] -
is the chara cter table of A 3. The table of S is real for e ach n.
I t s h o u l d b e m e n t i o n e d , t h a t S n, A a n d t h e w r e a t h p r o d u c t s o f
t h e f o r m C p ~ S n ( p a p r i m e , n _~ 3) a r e N a 6 a o - g r o u p s , i . e . t h e y a r e
t h e o n l y g r o u p s w i t h t h e s e c h a r a c t e r t a b l e s ( s ee N a g a o [ I] , O y a m a
[ 1 ] , Y o ko nu m a [ 1 ] ) .
F o r t h e c o n s t r u c t i o n o f th e r e p r e s e n t i n g m a t r i c e s s e e P u t t a s w a -
m a i a h [ I] a n d P u t t a s w a m a i a h / R o b i n s o n [ I] .
T h e s e t h e o r e m s c o n t a i n t h e r e s u l t s w e n e e d f r o m t h e o r d i n a r y r e -
p r e s e n t a t i o n t h e o r y o f S a n d A n . B e l o w w e s h a l l s u m m a r i z e
t h e r e s u l t s o f t h e m o d u l a r t h e o r y . T h e r e s u l t s f r o m t h e o r d i n a r y
t h e o r y s u f f i c e t o g i v e a de t a i l e d d e s c r i p t i o n o f t h e o r d i n a r y
r e p r e s e n t a t i o n t h e o r y o f G ~ S n . B u t b e f o r e d e r i v i n g t h i s t h e o ry ,
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 93/197
8 8
w e w o u l d l i k e t o c o n s i d e r t h e m o r e g e n e r a l c a s e G~ H , t h e g r o u n d -
f i e l d w i l l b e a s s u m e d t o b e a l g e b r a i c a l l y c l o s e d .
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 94/197
89
5 . R e p r e s e n t a t i o n s o f w r e a t h p r o d u c t s==
Let K denot~an al gebrai cally closed field, G a finite group and H
a permutati on group of degree n, i.e. a subgro up of S , the sym-
met ric gr oup on Q = [1,...,n].
W e w o u l d l i k e t o d e r iv e , h o w t h e i r r e d u c i b l e K - r e p r e s e n t a t i o n s o f
G~H can be constructed.
Fo r K = £,W. Spech t has done this in 1933 (Spe cht [2]) after ha-
vin g tre ated the special case G~S n (Specht [I]). Hi s res ults can
be generalized to groundf ields K of any characteristi c, if K is
assumed to be algeb raica lly closed. Using the theory of repres en-
t a t i o n s o f g r o u p s w i t h n o r m a l d i v i s o r s g i v e n b y A .H . C l i f f o r d i n
1937 (Clifford [I]) the deri vati on of the desire d results can be
shortened considerably (Kerber [2],[4]). We describe this
now.
W e a p p l y C l i f f o r d ' s t h e o r y t o t he n o r m a l d i v i s o r
G* = G I × ... × G _~ G~ H ,
the basis group of G~H, which is a direct product of n subgr oups
G i isom orphi c to G:
G = G i := ~(f;1 H) [ f: g ~ G, f(j) =1 G, V j$i} ~ G~ H
(cf. se cti on 2).
Since the groundfl eld K is assumed to be algebr aical ly closed,
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 95/197
9O
t h e i r r e d u c i b l e K - r e p r e s e n t a t i o n s o f G * a r e e x a c t l y t h e o u t e r t e n -
s o r p r o d u c t s
5 . 1 ~ * : = F 1 @ ' ' ' @ P n
o f i r r e d u c i b l e K - r e p r e s e n t a t i o n s F i o f G w i t h t h e r e p r e s e n t i n g
m a t r i c e s
5 . 2 F * ( f ; 1 H ) : = F 1 ( f ( 1 ) ) x . .. x P n ( f ( n ) ) ( K r o n e c k e r p r o d u c t ) .
A t f i r s t w e h a v e t o d e r i v e t h e i n e r t i a ~ G ~J ~F . o f t h i s r e p r e -
s e n t a t i o n F * , w h i c h i s d e f i n e d b y
5 .3 o ~ F . := C ( f ; ~ ) J F * ( ~ ; ~ ) ~ F * ~
( " ~" i n d i c a t e s e q u i v a l e n c y, F * ( f l g ) ( f ' ; 1 H ) : = P * ( f l ~ ) - 1 ( f ' l I g ) ( f ; ~ )
P * C f - ~ 1 f ' ~- l f~ - l; 1 H ) = F * ( c f - l f v f ) ~ - l ; 1 H ) )"
S i n c e G * ~ G ~ H F . t h i s g r o u p i s o b v i o u s l y a p r o d u c t
5 . 4 G ~ H F . = G * H ~ .
o f G * w i t h a s u b g r o u p H ~ . o f t h e c o m p l e m e n t H ' o f G* . H i . w i l l b e
c a l l e d t h e i n e r t i a f a c t o r o f F * :
5 - 5 H ~ . = [ ( e1 ~ ) J F ( e ; ~ ) ~ F * ] .
W e n o t i c e , t h a t
5 . 6 F * ( e ; ~ ) ( f ; I H ) = F * ( e ; ~ ) - 1 ( f ; I H ) ( e ; ~ ) = F * ( f _ I ; I H) •
T o d e s c r i be t h e i n e r t i a f a c t o r e x p l i c i t l y w e d i s t i n g u i s h t h e i r -
r e d u c i b l e K - r e p r e s e n t a t i o n s 5 .1 w i t h r e s p e c t t o t h e i r ty p e :
L e t P I , . . . , F r b e a f i x e d a r r a n g e m e n t o f th e r p a i r w i s e
i n e q u i v a l e n t K - r e p r e s e n t a t l o n s o f G .
W e c a l l F * = F I ~ . . . ~ P n t o b e o f t y p e ( n ) = ( n l , . . . , n r )
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 96/197
9 1
( w i t h r e s p e c t t o th e a b o v e a r r a n g e m e n t ) , i f n j i s t he
n u m b e r o f f a c t o r s P i o f P * e q u i v a l e n t t o P J .
L e t F * b e o f t y p e ( n) a n d l e t S n j b e t h e s u b g r o u p o f S ( >_ H) c o n -
s i s t i n g o f t h e e l e m e n t s p e r m u t i n g e x a c t l y t h e n j i n d i c e s o f t he
n j f a c t o r s F i o f P * w h i c h a r e e q u i v a l e n t t o F j . W e s e t
5.8 Sin ) .-= S'nl ×. .. × S'nr wit h S'nj := [(e;~) I ~ E Snj ] •
W e w o u l d l i k e t o p r o v e , w h a t i s s u g g e s t e d b y 5 .6 :
5 . 9 = E ' n S i n )
P r o o f : 5 . 2 a n d 5 . 6 i m p l y
F * C e ; ~ ) C f ; I H ) = F l ( f C ~ C 1 ) ) ) x . . .X F n C f C ~ C n ) ) ) •
T h e q u e s t i o n i s, f o r w h i c h ~ t h i s r e p r e s e n t a t i o n i s e q u i v a l e n t t o
F * . S i n c e P * a s w e l l a s p . ( e ; ~ ) a r e i r r e d u c i b l e r e p r e s e n t a t i o n s ,
w e c a n u s e a c h a r a c t e r - t h e o r e t i c a l a r g u m e n t .
' Si ) I f ~ E H N ( n) ' t h e n t h e t r a c e o f F i ( f ( ~ ( i ) ) ) i s e q u a l t o t h e
t r a c e o f P ~ ( i ) ( f ( ~ ( i ) ) ) . T h u s
t r ' F * ( f ; I H ) = t r P * ( e ; ~ ) ( f ; I H ) , V f , ~ F *F , ( e ; ~ )
H ' n s I = >
( i i ) I f t h e o t h e r w a y r o u n d ( e ; ~) i s a n e l e m e n t o f t h e i n e r t i a
f a c t o r , w e h a v e
t r P * ( f ; 1 H ) = t r F * ( e ; ~ ) ( f ; 1 H ) = t r P * ( f _ I ; I H ) , V f .
I f w e c h o o s e ( f ;1 H ) E G s u c h t h a t f ( j ) = I , V j ~i , t h e n
i n t h i s s p e c i a l c a s e
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 97/197
92
( j ~ i f j ) t r F i ( f ( i ) ) = ( j ~ ~ - l ( i ) f J ) t r F _ l ( i ) ( f ( i ) ) ( I)
w i t h t h e d i m e n s i o n s f J o f t h e f a c t o r s F j o f F * . A n d t h i s i s
v a l i d f o r e a c h f ( i ) E G .
L e t u s c o n s i d e r t h e a s s o c i a t e d B r a u e r c h a r a c t e r s ( i f c h a r K = p )
r e s p. t h e t r a c e s ( i f c h a r K = 0) i . W e a r e a l l o w e d t o s i m p l i f y
( I) s o t h a t w e o b t a i n
~ - I ( i )~ i ( f ( i ) ) f ~ - 1 ( i ) = ~ ( f ( i ) ) f i, V f(i) 6 G .
S i n c e t h e r o w s o f t h e c h a r a c t e r t a b l e s a n d t h e B r a u e r c h a r a c -
t e r s of i r r e d u c i b l e m o d u l a r r e p r e s e n t a t i o n s a r e l i n e a r l y i n d e -
p e n d e n t , w e o b t a i n
i = ~ - 1 ( i ) ~ F i N F _ i (i ) ~ ~ E S ( n ) ' n S l n
q.e.d.
F r o m t h i s w e o b t a i n f o r t h e i n e r t i a g r o u p :
5 . 1 0 G ~ H ~ . = G * ( H Q S ( n ) ) ' = G ~ ( H Q S ( n )) .
~ o l l o w i n g C l i f f o r d ' s t h e o r y w e n o w h a v e t o e x t e n d F * t o a r e p r e -
s e n t a t i o n o f i t s i n e r t i a g r o u p.
I t is n o t p o s s i b l e t o e x t e n d a l i n e a r r e p r e s e n t a t i o n o f a n o r m a l
d i v i s o r t o a l i n e a r r e p r e s e n t a t i o n o f t h e i n e r t i a g r o u p i n g e n e r a l .
W e c a n o f t e n e x t e n d i t t o a p r o j e c t i v e r e p r e s e n t a t i o n . B u t i n o u r
c a s e h e r e , w h e r e G * , t h e n o r m a l d i v i s o r , i s a s e m i d i r e c t f a c t o r
o f t h e i n e r t i a g r o u p , w e a r e f o r t u n a t e l y a b l e t o e x t e n d ~ * t o a
l i n e a r r e p r e s e n t a t i o n o f G ~ H F. . H o w t h i s c a n b e do n e, S p e c h t h a s
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 98/197
93
s h o w n ( S p e c h t [ ] ) .
W e c a n a s s u m e w i t h o u t r e s t r i c t i o n , t h a t e q u i v a l e n t f a c t o r s P i o f
P * a r e n o t o n l y e q u i v a l e n t , b u t e v e n e q u a l:
Fj ~ Pk ~ Pi (f(i)) = Pk(f (i)) , V f(i) ~ G ..11
I f n o w
5 . 1 2 F * C f ; 1 H ) = ( f l p l C f C 1 ) ) . . . f n p n C f C n ) ) )
i s t h e m a t r i x r e p r e s e n t i n g ( f ; 1H ) , t h e n w e s e t f o r ~ E H n S ( n ) :
5 . 1 3 ~ * ( f ; ~ ) : = (f~l~ _1 (f(1 )).. .f~n ~ _I (f(n))) ,
(1) (n)
a n d i t i s e a s y ~ o v e r i f y , t h a t t h e s e m a t r i c e s f o r m a r e p r e s e n t a -
t i o n ~ * o f G ~ H ~ . . S i n c e
~
5.14 F* G* = F* ,
t h i s r e p r e s e n t a t i o n i s i rr e d u c i b le .
N o w l e t F " b e a n i r r e d u c i b l e K - r e p r e s e n t a t i o n o f H n S ( n ) ( i f H ' n S ! n )
i s t h e i n e r t i a f a c t o r o f P * ) a n d F ' a c c o r d i n g t o
5.1 5 F'Cf; ) :=
t h e c o r r e s p o n d i n g r e p r e s e n t a t i o n o f t he i n e r t i a g r ou p . M u l t i p l y i n g
t h e s e tw o r e p r e s e n t a t i o n s t o g e t h e r , t h e r e s u l t
5 . 16 ~ * ® F '
w i t h t h e r e p r e s e n t i n g m a t r i c e s
5 . 1 7 ( ~ * @ P ' ) ( f ; ~ ) : = ~ * ( f ; ~ ) x F ' ( f ; ~ )
i s a n i r r e d u c i b l e K - r e p r e s e n t a t i o n o f G~ J~ p, , a s c a n b e s e e n w i t h
t h e a i d o f C l i f f o r d ' s t h e o r y .
T h e m o s t i m p o r t a n t r e s u l t i s, t h a t t he r e p r e s e n t a t i o n i n d u c e d b y
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 99/197
94
5 . 1 6 i s i r r e d u c i b l e :
~ P := ( ~* @ F ') ~ G ~ H i s i r r ed u c i bl e a nd e v er y i r r e du c i b le
K - r e p r e s e n t a t i o n o f G ~ H i s o f t h i s f or m .
I t r e m a i n s t o i n v e s t i g a t e , w h i c h r e p r e s e n t a t i o n s F * a n d P ' r e s p .
F " h a v e t o r u n t h r o u g h s u c h t h a t F r u n s e x a c t l y t h r o u g h a c o m p l e t e
s y s t e m o f p a i r w i s e i n e q u i v a l e n t a n d i r r e d u c i b l e K - r e p r e s e n t a t i o n s
of G~H.
U s i n g C l i f f o r d ' s n o t a t i o n , w e c a l l t wo i r r e d u c i b l e r e p r e s e n t a t i o n s
o f G ~ H a s s o c i a t e d ( w it h r e s p e c t t o G * ) , i f t h e i r re s t r i c t i o n s t o
G * h a v e a n i r r e d u c i b l e c o n s t i t u e n t i n c o mm o n . F r o m C l i f f o r d ' s
t h e o r y w e k n o w , t h a t t h e r e i s a l - l - c o r r e s p o n d e n c e b e t w e e n t h e
c l a s s e s o f a s s o c i a t e d r e p r e s e n t a t i o n s o f G ~ H a n d t h e c l a s s e s o f
r e p r e s e n t a t i o n s o f G * w h i c h a r e c o n j u g a t e s w i t h r e s p e c t t o G~ H .
T w o r e p r e s e n t a t i o n s F * a n d F * * o f G * a r e c o n j u g a t e s w i t h r e s p e c t
t_.o G~H, if t her e is an (f;~) E G~H so tha t
5.19 F* (f;~) N F** •
A n d t h i s c o r r e s p o n d e n c e i s as f o l l o w s : t h e r e s t r i c t i o n t o G * o f
e v e r y e l e m e n t o u t o f a c l a s s o f a s s o c i a t e d r e p r e s e n t a t i o n s i s
( u p t o i t s m u l t i p l i c i t y ) j u s t t h e c o r r e s p o n d i n g c l a s s o f c o n j u g a t e
r e p r e s e n t a t i o n s .
H e n c e i t s u f f i c e s , t h a t i n ~ t h e r e p r e s e n t a t i o n F * r u n s t h r o u g h
a c o m p l e t e s y s t e m o f r e p r e s e n t a t i v e s o f t h e cl a s s e s o f c o n j u g a t e
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 100/197
95
r e p r e s e n t a t i o n s o f G *. M o r e o v e r C l i f f o r d ' s t h e o r y yi e l d s , t h a t
a s s o c i a t e d r e p r e s e n t a t i o n s d i f f e r o n l y i n t h e f a c t or , w h i c h i s
a n i r r e d u c i b l e r e p r e s e n t a t i o n o f t h e i n e r t i a f a c t o r . H e n c e i t
s u f f i c e s , t h a t - w h i l e P * i s f i x e d - P ' r u n s t h r o u g h a c o m p l e t e
s y s t e m o f i r r e d u c i b l e K - r e p r e s e n t a t i o n s o f H ~ .. T h u s w e h a v e o b -
t a i n e d t h e f o l l o w i n g t h e o r e m :
5 . 2 0 T h e i r r e d u c i b l e K - r e p r e s e n t a t i o n F = ( ~* @ F ' ) t G ~ H r u n s
e x a c t l y t h r o u g h a c o m p l et e s y s t e m o f p ai r w i s e i n e q u i v a l e n t
a n d i r r e d u c i b l e K - r e p r e s e n t a t i o n s o f G ~ H i f F * r u n s t h r o u g h
a c o m p l e t e s y s t e m o f p a i r w i s e n o t c o n j u g a t e b u t i r r e d u c i b l e
K - r e p r e s e n t a t i o n s o f G * , an d , w h i l e P * i s f i x e d , F " r u n s
t h r o u g h a c o m p le t e s y s t e m o f p a i r w i s e i n e q u i v a l e n t K - r e p r e -
s e n t a t i o n s o f H O S ( n ) .
I n t h e s p e c i a l c a s e H = S t w o r e p r e s e n t a t i o n s o f G * ar e c o n j u -
g a t e s i f a n d o n l y i f t h e y a r e o f t h e s a m e t y p e. H e n c e F r u n s
t h r o u g h a c o m p l e t e s y s t e m o f i r r e d u c i b l e K - r e p r e s e n t a t i o n s o f
G ~ S n i f P * r u n s t h r o u g h a c o m p l e t e s y s t e m o f i r r e d u c i b l e K - r e p r e -
s e n t a t i o n s w i t h p a i r w i s e d i f f e r e n t t y p e s a n d P " - w h i l e P * i s
f i x e d - r u n s t h r o u g h a c o m p l e t e s y s t e m o f p a i r w i s e i n e q u i v a l e n t
a n d i r r e d u c i b l e K - r e p r e s e n t a t l o n s o f S ( n ).
T h u s t h e n u m b e r o f i r r e d u c i b l e o r d i n a r y r e p r e s e n t a t i o n s o f G ~S n
i s
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 101/197
96
5 .2 1 E p ( n . ) . . . p ( n s ) ," ' ( n ) '
i f s i s t h e n u m b e r o f c o n J u g a c y c l a s s e s o f G , p ( m) i s th e n u m b e r
of parti tio ns of m, p(O) := I, and if the sum is taken over all
the types (n) = (nl,...,ns).
T h i s a g r e e s w i t h 3 . 8, t h e n u m b e r o f c o n j u g a c y c l a s s e s o f G ~ S n .
O f c o u r s e 5 . 21 y i e l d s a l s o t h e n u m b e r o f i r r e d u c i b l e K - r e p r e s e n t a -
t i o n s i f c h a r K = p d o e s n o t d i v i d e I G~ Sn l a s l o n g a s K i s a l g e b r a -
ical ly closed. If charK = p I IG~Snl we have for the numbe r of ir-
r e d u c i b l e K - r e p r e s e n t a t i o n s o f G ~ S n:
Z p r ( n l ) . . . p r ( n t ) ,( n )
i f t i s t he n u m b e r o f p - r e g u l a r c l a s s e s o f G , p r ( m) i s t h e n u m b e r
o f p - r e g u l a r p a r t i t i o n s o f m ( i . e . p d o e s n ' t d i v i d e t h e e l e m e n t s
of the parti tion) , pr(0) := I, and the sum is taken over all the
types (n) = (nl,...,nt ).
A s a n e x a m p l e w e d e r i v e t h e i r r e d u c i b l e C - r e p r e s e n t a t i o n s o f t h e
n o r m a l i z e r o f $ 3× S 3 i n $ 6, w h i c h i s a f a i t h f u l p e r m u t a t i o n r e p r e -
sent atio n of $3~S 2 (cf. sect ion 3):
( i ) T h e r e p r e s e n t a t i o n s o f t h e b a s i s g r o u p S ~, t h e i r t y p e s ° i n e r t i a
g r o u p s a n d i n e r t i a f a c t o r s :
S ~ ~ S 3 x S 3 h a s t h e f o l l o w i n g i r r e d u c i b l e C - r e p r e s e n t a t i o n s :
[ 3 ] I [ 3 2 [ 3 2 ~ [ 2 , 1 ] [3 2 ~ [1 3 2 [ 2 , 1 2 ~ [ 3 ] [ 2 , 1 ] ~ [ 2 , 1 ]
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 102/197
97
[ 2 ,1 1 1 1 1 1 3 ] [ 1 3 1 1 1 1 3 ] [ 1 3 1 1 1 1 2 , 1 ] [ 1 3 1 1 1 1 1 3 ] .
W i t h r e s p e c t t o t h e a r r a n g e m e n t [ 3] , [ 2 , 1] , [ 1 3 ] o f t h e i r r e d u c i b l e
C - r e p r e s e n t a t i o n s o f $ 3, t h e t yp e s o f t h e s e r e p r e s e n t a t i o n s a r e
( 2 , 0 , 0 ) ( 1 , 1 , 0 ) ( 1 , 0 , 1 ) ( 1 , 1 , 0 ) ( 0 , 2 , 0 )
( 0 , 1 , 1 ) ( 1 , 0 , 1 ) ( 0 , 1 , 1 ) ( 0 , 0 , 2 ) •
H e n c e a c o m p l e t e s y s t e m o f i r r e d u c i b l e C - r e p r e s e n t a t i o n s o f S
w i t h p a i r w i s e d i f f e r e n t t y p e s is
[ [ 3 1 1 1 1 3 ] , [ 3 1 1 1 1 2 , 1 ] , [ 3 1 1 1 1 1 3 ] , [ 2 , 1 ] 1 1 1 2 ,1 ] , [ 2 , 1 1 1 1 1 1 3 ] , [ 1 3 1 1 1 1 1 3 1 1 .
T h e c o r r e s p o n d i n g i n e r t i a g r o u p s ar e :
s 3 , , ~ 2 , s ~ , s ~ , s 3 , s 2 , s - ~ , s 3 ~ 2 ,
t h e i n e r t i a f a c t o r s :
s t , , s . i , s ~ , s ~ , s ~ , s ~ .
( i i ) T h e r e p r e s e n t a t i o n s o f S 3 ~ $ 2 :
T h e i r r e d u c i b l e o r d i n a r y r e p r e s e n t a t i o n s o f S a r e [2 ] a n d [1 2] ,
t h e o n l y on e o f S i s [ I] . T h u s w e g e t f o r t h e i r r e d u c i b l e
c - r e p r e s e n t a t i o n s o f $3 , $ 2:
[ 3 1 1 1 1 3 ] ® [ 2 ] , = [ 3 1 1 1 1 3 ] ,
[ 3 1 1 1 1 3 ] ® [ 1 2 ] ' ,
([311112,1] @ [1]'I t $3" S 2 = [3] #[2 ,1] ~ $ 3'~ 2 ,,
( [ 3 ] # [ i 3 ] ~ [ 1 ] , I I' s 3 - s 2 = [ 3 1 1 1 [ I 3 ] f s 3 - s 2 ,
[ 2 , 1 1 1 1 1 2 , 1 ] ® [ 2 ] ' = [ 2 , 1 ] # [ 2 , 1 ] ,
[ 2 , 1 ] ~ [ 2 , 1 ] ® [ 1 2 ] , ,
( [ 2 , 1 ] # [ I 3 ] ® [ I ] ' ) ~ ' 8 3 - 8 2 = [ 2 , 1 ] # [ 1 3 ] t 8 3 " S 2 ,
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 103/197
9 8
[ 1 3 ] , [ 1 z ] ® [ 2 ] , = [ l Z ] , [ 1 3 ] ,
[ 1 3 ] ~ [ 1 3 ] @ [ 1 2 ] ' .
T h e i r d e g r e e s a r e 1 ,1 , 4 , 2 , 4 ,4 , 4 , 1 , 1 i n a c c o r d a n c e w i t h
1 2 + 1 2 + 4 2 + 2 2 + 4 2 + 4 2 + 4 2 + 1 2 + 1 2 = 7 2 = I S 3 ~ $ 2 1 .
( i i i ) R e p r e s e n t i n 6 m a t r i c e s :
A s a n u m e r i c a l e x a m p l e w e s h a l l e v a l u a t e t h e m a t r i x o f
[ 2 , 1 ] ~ [ 2 , 1 ] @ [ 1 2] ' r e p r e s e n t i n g ( 1 4 ) ( 2 5 ) ( 3 6 ) , t h e i m a g e o f
( e ; ( 1 2 ) ) u n d e r t h e p e r m u t a t i o n r e p r e s e n t a t i o n o f $ 3 ~ S 2 . (T o
g e t a l l t h e e l e m e n t s o f a r e p r e s e n t a t i o n i t s u f f i c e s t o e v a l u a t e
t h e m a t r i c e s r e p r e s e n t i n g g e n e r a t i n g e l e me n t s . F o r g e ne r a t o r s o f
w r e a t h p r o d u c t s S m % S " s e e N e u m a n n [ I] .)
F i r s t , u s i n g t h e r e s u l t s o f s e c t i o n 4 , w e o b t a i n t h e m a t r i x e f
[ 2 , 1 ] ~ [ 2 , 1 ] r e p r e s e n t i n g ( e ; 1 ) :
[ 2 , 1 ] ~ [ 2 , 1 ] ( e ; 1 ) =
12 13 45 463 2 6 5
[: : ] [ : :]
12 45 12 46 13 45 13 463 6 3 5 2 6 2 5
1 2 ( 1 ) ) .= ( f ~ 1 ~ 1 ( 1 ) f ~ 2 P 2
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 104/197
99
=~ [ 2 , 1 ] I I [ 2 , 1 ] ( e ; ( 1 2 ) ) = ( f 1 1 ~ 2 ( 1 ) f 2 2 1 3 1 ( 1 ) ) = 0 11 0
O 0
(We have to permut e the second and third colllmn.)
O n a c c o u n t o f [ 1 2 ] ( 1 2 ) = ( - 1 ) w e o b t a i n t h e r e f r o m :
r 2 0 1 1 # r 2 , 1 1 r 2 1, o o 1 o
1 0 0
0 0 1
° °
0 - 1
- 1 0
0 0 -
x [ - 1 ]
T h i s i s a d e t a i l e d d e s c r i p t i o n o f t h e e x a m p l e R o b i n s o n g a v e ( R o -
binson [5], 3.515).
H a v i n g n o w g i v e n a c o m p l e t e a n d d e t a i l e d d e s c r i p t i o n o f t h e
c o n s t r u c t i o n o f t h e i r r e d u c i b l e r e p r e s e n t a t i o n s o f G ~ H o v e r an
a l g e b r a i c a l l y c l o s e d f i e l d w e m a y n o w t u r n t o s p e c i a l c a s e s .
T h e p r o c e d u r e b e c o m e s m u c h s i m p l e r i f G i s a n a b e l i a n g r o u p . S p e -
c i a l c a s e s o f t h i s, n a m e l y w r e a t h p r o d u c t s o f t h e f o r m C m ~ S n r e s p .
C m ~ A o f c y c l i c g r o u p s w i t h s y m m e t r ic r e sp ° a l t e r n a t i n g g r o u p s
h a v e b e e n c o n s i d e r e d b y Y o u n g, R o b i n s o n , O s im a , P u t t a s w a m a i a h a n d
F r a m e ( s e e Y o u n g L I ], R o b i n s o n [ 1] , O s i m a [ I ] , [ 3] , P u t t a s w a m a i a h
[ 1 ] , [ 2 ], F r a m e [ I] ), w h o s e r e s u l t s c a n n o w b e g e n e r a l i z e d .
I f G i s a b e l i a n , E * i s o n e d i m e n s i o n a l s u c h t h a t
5 . 2 3 ~ * ( f; ~ ) = F* C f; 1 H ) = ~ F i C f C i ) ) -l
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 105/197
1 0 0
I f ~ 1 , .. . ,~ i H: H fl S (n ) l i s a c o m p l e t e s y s t e m o f r e p r e s e n t a t i o n s o f
t h e l e f t c c s e t s o f t h e i n e r t i a f a c t o r H Q S ( n ) o f F * i n H a n d F " i s
a n i r r e d u c i b l e r e p r e s e n t a t i o n o f H n S ( n ) w e d e n o t e ( s ee t h e n o t a t i o n
o f O u r t i s / R e i n e r [1 ]) :
I -( g* @ P ' ) ( f - 1 ; ~ i l ~ k )' i f
( ~ * ® F ' ) C f - 1 ; ~ 1 1 ~ Z k ) : = ~ i - 1~ i ~ i ~ k E S ( n )
0 e l s e w h e r e .
W i t h t h i s n o t a t i o n a n d 5 . 2 3 w e o b t a i n , i f G i s a b e l i a n :
F ( f; ~ ) = ( ( ~* @ F ' ) ( f _ 1 ; ~ [ 1 ~ k ))
= ( F * ( f _ ~ l u ) 9 " ( q 1 ~ k ) )~ i I
i f
" 1 { F " C ~ [ 1 ~ k ), i f ~ [ I ~ k E HG S ( n )
0 , e l s e w h e r e
S i n c e
w e h a v e o b t a i n e d
~ . 2 4 I f G i s a b e l i a n w e h a v e f o r t h e r e p r e s e n t i n g m a t r i c e s o f
P = ( ~ * ® F ' ) ? Q ~ :
F ( f ; ~ ) = ( F * C f - 1 ; I H ) ' ~ " ( q l Q ) ,
i . e . t h a t t h e [ H : S ( n ) [ 2 s u b m a t r i c e s o f w h i c h t h i s m a t r i x
c o n s i s t s a r e u p t o t h e n u m e r i c a l f a c t o r s F * ( f - I ; 1 H )
~ i
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 106/197
101
e q u a l t o t h e s u b m a t r i c e s o f w h i c h t h e m a t r i x ( F" t H ) ( ~ )
c o n s i s t s .
T h e e v a l u a t i o n o f t h e m a t r i c e s o f F " $ H h a s b e e n d e s c r i b e d f o r
t h e s p e c i a l c a s e H = S i n 4 . 4 9 i n c a s e t h a t t h e r e a r e o n l y t w o
f a c t o r s , w h a t c a n e a s i l y b e g e n e r a l i z e d .
T h i s m e t h o d d e s c r i b i n g t h e c o n s t r u c t i o n o f t h e m a t r i c e s o f t h e i r -
r e d u c i b l e r e p r e s e n t a t i o n s o f G ~ f o r a n y a b e l i a n G g e n e r a l i z e s t h e
r e s u l t ~ o f P u t t a s w a m a i a h f o r C m ~ S n ( P u t t a s w a m a i a h [ 2] ) t o w r e a t h
p r o d u c t s G ~ S n, G a b e l i a n , a n d t h e r e s u l t s o f F r a m e o n C 2 ~ S n
(Frame [I]).
L e t u s r e t u r n t o 5 . 1 8 . T h i s t h e o r e m d e s c r i b e s , h o w w e c a n g et t h e
i r r e d u c i b l e K - r e p r e s e n t a t i o n s o f G ~ H f r o m th e i r r e d u c i b l e K - r e p r e -
s e n t a t i o n s o f G a n d th e i r r e d u c i b l e K - r e p r e s e n t a t i o n s o f c e r t a i n
s u b g r o u p s H N S ( n ) of H . T h u s t h e r e p r e s e n t a t i o n t h e o r y o f S m ~ S n c a n
h e d e r i v e d t o a l a r g e e x t e n t w i t h t h e a i d o f t h e r e p r e s e n t a t i o n
t h e o r y o f th e s y m m e t r i c g r o u p . T h i s w i l l b e s h o w n b e l o w , w h e r e
w e s h a l l c o n s i d e r e s p e c i a l l y t h e r e p e r c u s s i o n o f t hi s f a c t on t h e
r e p r e s e n t a t i o n t h e o r y o f t h e s y m m e t r i c g r o u p , f o r e x a m p l e o n t h e
t h e o r y of t h e s y m m e t r i z e d o u t e r p r o d u c t s [ ~ ] Q [ ~ ] o f i r r e d u c i b l e
o r d i n a r y r e p r e s e n t a t i o n s L ~ a n d E ~] o f s y m m e t r i c g r o u p s .
T o g e n e r a l i z e t h i s t h e o r y o f s y m m e t r i z e d o u t e r p r o d u c t s o f s y m m e -
t r i c g r o u p s w e p o i n t n o w t o c e r t a i n i r r e d u c i b l e r e p r e s e n t a t i o n s
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 107/197
102
o f G ~ H w i t h t h e a id o f w h i c h w e s h a l l d e f i n e s y m m e t r i z e d o u t e r p r o -
d u c t s f o r a n y r e p r e s e n t a t i o n s o f a n y p e r m u t a t i o n g r o u p s s u c h t h a t
[ a ] Q [ ~ ] i s a s p e c i a l ca s e.
A t f i r s t w e i n d i c a t e c e r t a i n i r r e d u c i b l e K - r e p r e s e n t a t i o n s o f G ~
b y a s p e c i a l n o t a t i o n : I f P * i s o f t y p e ( 0 , . . . , O , n , O , . . . , O ) , i . e.
i f a l l t h e f a c t o r s F i o f F * = ~ P i a r e e q u i v a l e n t t o a c e r t a i n i r -
r e d u c i b l e K - r e p r e s e n t a t i o n o f G , s a y t o P J , t h e n w e d e n o t e t h i s b y
5 . 2 5 ( F S ; P ,,) : = ~ S ~ . . . ~ F j ® P ,
n(The ine rti a fac tor of F* ~ PJ is H' ' ', P"OS = H hen ce is an ir-
r e d u c i b l e K - r e p r e s e n t a t i o n o f H . )
T h e s p e c i a l c a s e o f t h e r e p r e s e n t a t i o n s ( a; ~) o f a s u b g r o u p S m ~ S n
o f S m n ( c f. 2 . 3 3 ) p l a y s a n i m p o r t a n t r o l e i n t h e o r d i n a r y r e p r e s e n -
t a t i o n t h e o r y o f t h e s y m m e t r i c g r o u p . T h e i n d u c e d r e p r e s e n t a t i o n s
( ~| ~) ~ S m u = : [ ~ ] G [ ~ ] a r e t h e s o - c a l l e d s y m m e t r i z e d o u t e r p r o -
d u c t s o f i r r e d u c i b l e C - r e p r e s e n t a t i o n s o f s y m m e t r i c g r o u p s ( of .
s e c t i o n 6 ). T h u s w e g e t i n a n a t u r a l w a y t h e f o l l o w i n g g e n e r a l i z a -
t i o n o f t h is c o n c e p t ( K e r b e r [ 4] ):
. ~ L e t G _K Sm , H<_S . T h e n w e c an i d e n t i f y G ~ w i t h a s u b g r o u p o f
S m n ( cf . 2 . 2 4 / 2 . 2 5 ) , a n d i f P G a n d F a r e a n y t w o K - r e p r e s e n -
t a t i o n s o f G a n d H ( f o r a n y g r o u n d f i e l d K ) , t h e n w e c a l l
~ Q e F H : = ( F O ; F H ) t S tu n = ( ~ ~ a ) ® ~ ~ S t u n
t h e s 2 m m e t r i z e d o u t e r p r o d u c t o f F a n d F .
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 108/197
1o3
A r u l e w h i c h is o b v i o u s f r o m t h e f o r e g o i n g c o n s i d e r a t i o n s i s: If
P H~ Z ~ k
k
i n d i c a t e s t h e d e c o m p o s i t i o n o f P H i n t o i r r e d u c i b l e c o m p o s i t i o n
f a c t o r s , t h e n o b v i o u s l y P G ® P H h a s t h e s a m e d e c o m p o s i t i o n a s
z CFG® kl
k
H e n c e i n ca s e o f c o m p l e t e r e d u c i b i l i t y t h e s y m m e t r i z e d o u t e r p r o -
d u c t m u l t i p l i c a t i o n i s a d d i t i v e o n th e r i g h t h a n d s i de :
5 . 2 7 I f H i s c o m p l e t e l y r e d u c i b l e o v e r K, t h e n
z .
k k
T h i s g e n e r a l i z e s a w e l l k n o w n r u l e f o r t h e s y m m e t r i z e d o u t e T pr o -
d u c t o f c - r e p r e s e n t a t i o n s o f s y m m e t r i c g r o u p s .
W e w o u l d l i k e t o c o n s i d e r t h e c h a r a c t e r s o f G ~ H f o r a m o m e n t t o
d e r i v e s o m e o f t h e i r p r o p e r t i e s w h i c h w i l l b e o f u s e l a t e r o n .
I f t h e f a c t o r F * o u t o f P = ( 9 * @ P ' ) ~ G ~ H i s o f t y p e ( n) = ( n I ,
. o , nr ) , t h e n o b v i o u s l y e v e r y e l e m e n t ( f ;~ ) w h o s e p e r m u t a t i o n ~ h a s
a p a r t i t i o n P ~ w h i c h i s n o t a s u b p a r t i t i o n o f t h e t y p e ( n) h a s
z e r o a s c h a r a c t e r v a l u e u n d e r F :
~ . 2 8 I f t h e f a c t o r P * o u t o f P = ( 9 * @ F ' ) ~ G ~ i s o f t y p e ( n ) =
( n l , . . . , n r ) , t h e n a l l t h e e l e m e n t s ( f ;~ ) h a v e 0 a s c h a r a c t e r
v a l u e u n d e r P w h o s e c o n J u g a c y c l a s s h a s a n e m p t y i n t e r s e c t i o n
w i t h S ( n .
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 109/197
104
N o r u n d e r t h i s a s s u m p t i o n n o t a n y o n e o f t h e c o n j u g a t e s
C e ; ~ i ) - I C f ; ~ l C e ; ~ i ) -- ( f i I ; ~ I ~ i )
o f ( f ;~ ) i s c o n t a i n e d i n t he i n e r t i a g r o u p f r o m w h i c h P i s i n d u c e d ,
s i n c e f o r e ~ e r y i: ~ i 1 ~ i ~ H G S ( n ) . T h u s w e h a v e o n l y O - m a t r i c e s
a l o n g t h e l e a d i n g d i a g o n a l o f N ( f ; ~) .
q.e.d.
T h e d i f f i c u l t y o f g e t t i n g t he c h a r a c t e r s o f w r e a t h p r o d u c t s
e x p l i c i t l y , e x c e p t f o r s p e c i a l c a s es , a r i s e s f r o m t h e f a c t t h a t
t o p a s s f r o m N * ( f ; I H ) t o ~ * ( f ; ~ ) w e h a v e t o p e r m u t e t h e c o l u m n s
o f N * ( f ; I H ) s o t h a t t h e l e a d i n g d i a g o n a l w i l l b e d i s t u r b e d . N o r
a d i s c u s s i o n o f t h e e v a l u a t i o n o f t h e s e c h a r a c t e r s t h e r e a d e r
i s r e f e r r e d t o L i t t l e w o o d [ 3] . A u s e f u l r e m a r k i s:
5 . 2 9 I f ~ i s a n n - c y c l e t h e n t h e c h a r a c t e r o f ( f; ~) v a n i s h e s u n d e r
a l l t h e i r r e d u c i b l e r e p r e s e n t a t i o n s o f G ~ H w h i c h a r e n o t o f
the form (PJ;P").
U n d e r ( P J ;P " ) t h e e l e m e n t ( e; ~) h a s t h e c h a r a c t e r v a l u e
C ( p J ; F , , ) ( e ; ~ ) ~ ¢ N " ( ~ ) ,
if f ~ is the dim ens ion of N j.
P r o o f : T h e f i r s t s t a t e m e n t f o l l o w s f r o m 5 . 28 .
F u r t h e r m o r e w e k n o w t h a t
(FJ;F") (e;~) = E x "(~) .
( n
A n d i n t h i s f i r s t f a c t o r o n th e r i g h t h a n d s i d e, w h i c h a r i s e s
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 110/197
105
f r o m t h e ( f~ J) n- ro we d~ i d e n t i t y m a t r i x b y c e r t a i n c o l l m ~ e r m u t a t i o n s
t h e l e a d i n g d i a g o n a l c o n t a i n s , e x c e p t O ' s ~ a s m a n y 1 ' s a s is t h ep J F J
d i m e n s i o n o f P J , f o r e x a c t l y t h e e l e m e n t s f i i . . . f i i ( 1 ~ i ~ f F j )
r e m a i n i n t h i s l e a d i n g d i a g o n a l ( cf . 5 . 1 3 ) .
q . e . d .
W e w o u l d l i k e n o w t o d e r i v e s o m e r e s u l t s c o n c e r n i n g t h e m o d u l a r
r e p r e s e n t a t i o n t h e o r y o f w r e a t h p r o d u c t s ( cf . K e r b e r [ 21 ) w h i c h
w i l l b e o f u s e l a t e r o n i n a p p l y i n g t h i s t h e o r y t o t h e m o d u l a r
r e p r e s e n t a t i o n t h e o r y o f t h e s y m m e t r i c g r o u p .
F i r s t w e c o n s i d e r t h e c a s e w h e r e G i s a p - g r o u p . T h e n G ~ c o n -
t a i n s w i t h i t s b a s i s g r o u p a n o r m a l d i v i s o r w h i c h i s a p - g r o u p
a s w e l l a s i t s c e n t r a l i z e r i f G $ ~ I ~ .
Fo r if (f;IH) E G i, f $ e, ~ $ I, we h ave
I $ (e; ~)( f;I H)( e;~ ) -1 = (f~;1 H) E G -I $ Gi -( i )
H e n c e t h e f o l l o w i n g i s v a l i d :
5 . 3 O G ~ [ I~ ~ C Q ~ ( G * ) ~ G * .
T h u s w e c a n a p p l y a l e m m a o f B r a u e r ( B r a u e r [ 11 , l e m m a 2 ) w h i c h
s a y s , t h a t a g r o u p p o s s e s s e s e x a c t l y o n e p - b l o c k i f i t c o n t a i n s
a n o r m a l p - g r o u p w h i c h i n c l u d e s i t s o w n ce n t r a l i z e r . W e h a v e
o b t a i n e d :
5 . 31 I f G $ ~I ] i s a p - g r o u p , t h e n G ~ H p o s s e s s e s e x a c t l y o n e
p - b l o c k .
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 111/197
1 0 6
F u r t h e r m o r e i n t h i s c as e th e o nl y i r r e d u c i b l e p - m o d u l a r r e p r e s e n -
t a t i o n o f G * i s t h e i d e n t i t y r e p r e s e n t a t i o n s o t h a t e a c h p - m o d u -
l a r i r r e d u c i b l e r e p r e s e n t a t i o n o f G ~ H i s o f t h e f o r m
5.32 IG* @ F' = P' •
S i n c e G ~ H = G * H ' , t h e p - r e g u l a r e l e m e n t s a r e c o n t a i n e d i n H ' s o
t h a t a n o r d i n a r y i r r e d u c i b l e r e p r e s e n t a t i o n o f G ~ H h a s th e sa m e
B r a u e r c h a r a c t e r a s i ts r e s t r i c t i o n t o H ' :
I f G i s a p - g r o u p , t h e n a p - m o d u l a r r e p r e s e n t a t i o n a s s o c i a t e d
w i t h a n o r d i n a r y i r r e d u c i b l e r e p r e s e n t a t i o n P o f G ~ h a s th e
s a m e d e c o m p o s i t i Q n n u m b e r s a s F $ H ' .
I n c a s e t h a t G i s a n a b e l i a n p - g r o u p , t h e f a c t o r F * i s o n e d i m e n -
s i o n a l s o t h a t
~ * ( f ; ~ ) = F * ( f ; 1 H )
a n d th e a s s o c i a t e d p - m o d u l a r r e p r e s e n t a t i o n i s t h e i d e n ti t y r e -
p r e s e n t a t i o n . H e n c e t h e f o l l o w i n g i s v a l i d :
5 ~ I f G i s a n a b e l i a n p - g r o u p , t h e n a p - m o d u l a r r e p r e s e n t a t i o n
a s s o c i a t e d w i t h th e o r di n a r y i r r e d u c i b l e r e p r e s e n t a t i o n F =
( ~ * @ F ' ) ~ G ~ H h a s t h e s a m e d e c o m p o s i t i o n n u m b e r s a s
p - m o d u l a r r e p r e s e n t a t i o n a s s o c i a t e d w i t h F " ~ H .
A s a n e x a m p l e we w o u l d l i k e t o e v a l u a t e t h e d e c o m p o s i t i o n m a t r i x
o f $ 2 ~ S 3 w i t h r e s p e c t t o p = 2 .
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 112/197
~)
~
=
-
~
13
O
--~
O
--~
--~
-~
-~
-~
"~
O
-~
~
O
0
0
-~
~
"~
~
0
0
~
~1
iI
"~
!
O
O
~
O
O
~
C/~
el"
H"
H-
O
O
O
~
c+
¢D
d"
O
(I)
~-
"4
e
I
~
I~
I
!
--~
~
~
cf
O
®
®
6'--"I f--~ I'-'-I --~
Ct~
IX)
h)
.
~
ID"
h)
~
"e~
~
r
.
0"
-
0
0
O
~
.~
~
~
~
~
~
I
,~
,d'
O
,~-
v
~-~
~
0
~
d-
h)
,~
Z
r~
0
~
~.~
e
-~
~
0
c+
-
H.
I
0
c
I11
¢~
~
I
I1
0
~:~
c+
-
~~
0 ,1
I
0 e
~
N
m
t !
0
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 113/197
1 0 8
I f o n t h e o t h e r h a n d t h e o r d e r IGI o f G i s r e l a t i v e l y p r i m e t o p ,
t h e s i t u a t i o n i s q u i t e d i f f e r e n t . F o r t h e n e v e r y p - m o d u l a r r e p r e -
s e n t a t i o n a s s o c i a t e d t o ~ * i s i r r e d u c i b l e s i n c e ~ * ~ G * = F * i s
i r r e d u c i b l e a n d w e o b t a i n w i t h a l e m m a o f 0 s i m a ( O s i m a [ 3] ,
l e m m a 5 ) :
5.56 If (IGI,p) = 1 t h e p - b l o c k o f G a S t o w h i c h F = ( ~ * ® F ' ) $ G a S
b e l o n g s h a s t h e s am e d e c o m p o s i t i o n m a t r i x a s t h e b l o c k o f
t h e i n e r t i a f a c t o r t o w h i c h F " b e l on g s .
( ~ * ® P ~ ) t G a S a n d ( ~ * @ F ~ ) ~ G a S b e l o n g t o t h e s a m e b l o c k
o f G a S i f a n d o n l y i f F~ a n d P ~ b e l o n g t o t he s a m e b l o c k o f
t h e i n e r t i a f a c t o r H ' G S ( n ) of P * .
U s i n g t h i s a nd t h e w e l l k n o w n d e c o m p o s i t i o n m a t r i x
E2, ]
[ 1 3 ]
o f S w i t h r e s p e c t t o p = 3 w e o b t a i n a s d e c o m p o s i t i o n m a t r i x o f
8 2 % S 3 f o r p = 3 a n d t h e s a m e a r r a n g e m e n t a s i n 5 . 3 5 o f t h e r o w s :
1 0
1 1
0 1
5 . 3 7
1
1
1
1 0
1 1
0 1
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 114/197
1 0 9
I t is m o r e d i f f i c u l t t o e v a l u a t e t h e d e c o m p o s i t i o n m a t r i x i f
n e i t h e r G i s a n a b e l i a n p - g r o u p n o r ( I G I ,p ) = I. B u t s i n c e 5 . 1 8
i s i n d e p e n d e n t o f t h e c h a r a c t e r i s t i c w e c a n s o m e t i m e s p r o c e e d
u s i n g th i s f a c t . A s a n e x a m p l e w e e v a l u a t e t h e d e c o m p o s i t i o n m a -
trix of S3%S 2 for p = 2.
[ 3] a n d [ 2 , i i a r e t h e 2 - m o d u l a r i r r e d u c i b l e r e p r e s e n t a t i o n s o f S 3 ,
[2] is the only one of 8 . Hen ce
[ 3 ] ~ [ 3 ] ® [ 2 ] ' ,
( [ 3 ] @ [ 2 , 1 ] ® ( [ 1 ] @ [ 1 1 / ' / t 8 3% 8 2 = [ '3 " ] ~ [ 2 , i' ]" '~ S 3"vS2 ,
[ 2 , 1 1 1 1 1 2 , 1 ] ® [ 2 ] ,
a r e t h e 2 - m o d u l a r i r r e d u c i b l e r e p r e s e n t a t i o n s o f S 3 % S 2.
T h e t a b l e o f B r a u e r c h a r a c t e r s o f th i s g r o u p i s t h e r e f o r e
[ 3 1 1 1 1 3 ] ® [ 2 ] ,V
[2,1]II[2,1] ® [2] '
[ 3 ] ~ [ 2 , 1 ] t $ 3 '~ 2
( 1 , 1 ;1 1 ( ( 1 2 3 1 , 1 ; 1 1 ( ( 1 2 3 1 , ( 1 2 3 1 ; 1 1
1 1 1
4 - 2 1
4 1 - 2
P r o m t h i s i t f o l l o w s t h a t
( 3 ; 2 )( 3 ; 1 2 )(13;1 2 )
(13;2)
( 2 , 1 ; 2 1
5 . 3 8 ( 2 , 1 ; 1 2 )
[ 3 1 1 1 1 2 , 1 ] 1 ' s 3 % s 2[ 3 ] t t [ 1 3 ] 1' S 3 % 82
[ 2 , 1 1 t i [ 1 3 ] 1" 8 3 % 8 2
"1 0 01 0 0
1 0 0
1 0 0
0 1 0
0 1 0
0 0 1
2 0 0
0 0 1
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 115/197
110
is the de compos ition ma trix of $3~S 2 for p = 2 (of. also the
character table of $3~S 2 in section 6).
Conclu ding this section we point once mere to the constru ction
of the irreducible represe ntatio ns of G~H.
I f w e k n o w h o w t o c o n s t r u c t t h e i r r e d u c i b l e r e p r e s e n t a t i o n s o f G
and of the subgroups HnS( n ) of H we get the repre sentin g matrice s
P ( f ; ~) a s w e h a v e d e s c r i b e d a b ov e : F i r s t w e f o r m K r o n e c k e r
products of irreducible K-rep resen tatio ns of G (see 5.1/5.2), then
we have to permute the columns of these matri ces (see 5.13). Aft er
this we have to form Krone cker produc ts once more (see 5.17) and
at last we have to induce (see 5.18) to get P(f;~).
Hence the entries of P(f;~) have all the properties wh ich are pro-
perties of the entries of the irreducible repre senta tions of G
and HO S(n ) and w hich are invariant with respect to col~imn permu-
t a t i o n a n d t h e K r o n e o k e r p r o d u c t m u l t i p l i c a t i o n a s we l l a s t h e
inducing process.
Prom this consid eration we get some results about spl itting
fiel ds (of. Ke rbe r [7]):
5.39 If S c K (K algebr aicall y closed) is a splittin g field for G
and the subgroups HNS(nl, then S is a splitting field for
G~H, too, i.e. every irreducible K-repres enta tion of G~H is
realizable in S.
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 116/197
111
E . g . if a l l t he o r d i n a r y i r r e d u c i b l e r e p r e s e n t a t i o n s o f G a n d o f
t h e s u b g r o u p s H O S ( n ) a r e r e a l i z a b l e i n ~ ( r e s p. Q ), t h e n a l l t h e
o r d i n a r y i r r e d u z i b l e r e p r e s e n t a t i o n o f G ~ H ar e r e a l i z a b l e i n R
( r e sp . Q ) a s w e l l . T h u s f o r e x a m p l e a l l t h e o r d i n a r y i r r e d u c i b l e
r e p r e s e n t a t i o n s o f S m ~ S n a r e r e a l i z a b l e i n Q a n d h e n c e e v e n i n N.
A w e a k e r a s s u m p t i o n w o u l d b e t h a t t h e o r d i n a r y c h a r a c t e r s o f G a s
w e l l a s o f t h e s u b g r o u p s H n S ( n ) a r e r e a l . B u t i t i s p o s s i b l e, t h a t
t h i s i s n o t c a r r i e d o v e r t o G ~ H s i n c e t h e l e a d i n g d i a g o n a l i s
d i s t u r b e d w h e n p a s s i n g f r o m F * ( f ; I H ) t o ~ * ( f ; E ) . W e k n o w t h a t t h e
r e a l i t y o f t h e o r d i n a r y c h a r a c t e r s i s e q u i v a l e n t t o t h e a m b i v a -
l e n c y o f t h e g r o u p . A n d a s w e h a v e p r o v e d i n s e c t i o n 3 ( c f . 3 . 1 4 )
G ~ S n i s a m b i v a l e n t i f G i s a m b i v a l e n t . T h u s w e h a v e , t h o u g h t h i s
d o e s n ot f o l l o w f r o m t h e c o n s t r u c t i o n o f t h e m a t r i c e s ( K e r b e r [ 7 ] ~ :
5 . 4 0 I f t h e c h a r a c t e r s o f G a r e r e a l , t h e c h a r a c t e r s o f G ~ S n a r e
r e a l a s w e l l .
F r o m 3 . 1 6 w e g e t:
5 . 4 1 I f t h e ( o r d i n a r y ) c h a r a c t e r t a b l e o f G o r o f H i s n o t r e a l ,
t h e n t h e c h a r a c t e r t a b l e of G ~ i s c o m p l e x .
A f i n i t e g r o u p i s c a l l e d a n M - _ ~ , i f e v e r y i r r e d u c i b l e r e p r e -
s e n t a t i o n o v e r a n a l g e b r a i c a l l y c l o s e d f ie l d wh o s e c h a r a c t e r i s t i c
d o e s n ' t d i v i d e I S l i s i n d u c e d b y a o n e d i m e n s i o n a l r e p r e s e n t a t i o n
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 117/197
112
o f a s u i t a b l e s u b g r o u p . A n o t h e r c o r o l l a r y t o 5 . 1 8 c o n c e r n i n g t h i s
c o n c e p t i o n i s ( S e i t z [ 1] , K e r b e r [ 61 ):
5 . 4 2 I f G a n d t h e s u b g r o u p s H G S ( n ) a r e M - g r o u p s , t h e n G ~ H i s a n
M - g r o u p .
P r o o f : I f K i s a l g e b r a i c a l l y c l o s e d a n d c h a r K ~ I G I , t h e n e v e r y
i r r e d u c i b l e K - r e p r e s e n t a t i o n o f G a n d h e n c e a l s o o f G * i s e q u i v a -
l e nt t o a r e p r e s e n t a t i o n , w h o s e m a t r i c e s c o n t a i n i n e v e r y r o w a n d
i n e v e r y c o l u m n e x a c t l y o n e n o n v a n i s h i n g e n t r y . T h i s i s v a l i d f o r
F * a s w e l l a s f o r ~ " a n d t h i s i s a p r o p e r t y i n v a r i a n t u n d e r c o l u m n
p e r m u t a ti o n , K r o n e c k e r p r o d u c t m u l t i p l i c a t i o n a n d t h e i n d u c i n g
p r o c e s s . H e n c e i t i s a p r o p e r t y o f F * a n d F " a n d ~ * ® F ' a n d
F = ( ~ * ® P ' ) t G ~ H . F r o m a w e l l k n o w n t h e o r e m ( s ee H u p p e r t [ I] ,
V, 18.9) it follows, that since E is irredu cible, ~ is induced
b y a o n e d i m e n s i o n a l r e p r e s e n t a t i o n o f a s u i t a b l e s u b g r o u p .
q.e.d.
E . C . D a d e h a s p r o v e d t h i s f o r t h e s p e c i a l c a s e H = C p = < ( 1 . . . p ) >
S p ( p a p r i m e n u m b e r , s e e H u p p e r t [ I] , V , 1 8 . 1 0 ) a s a n i m p o r t a n t
p a r t o f h i s p r o o f , t h a t e v e r y s o l v a b l e g r o u p c a n be i m b e d d e d i n
s a M - g r o u p ( s e e H u p p e r t [ 1 ] , V , 1 8 . 1 1 ) .
T h e l a s t 4 t h e o r e m s a r e c o r o l l a r i e s o f t he c o n s t r u c t i o n o f t h e
i r r e d u c i b l e r e p r e s e n t a t i o n s o f G ~ H w e h a v e g i v e n a b o ve . A n o t h e r
t h e o r e m c o n c e r n i n g g e n e r a l i z e d d e c o m p o s i t i o n n u m b e r s w i l l b e g iv e n
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 118/197
113
i n s e c t i o n 8 .
W i t h t h e a i d o f t he r e s u l t s o f t h i s s e c t i o n w e w o u l d l i k e n o w t o
d e s o r i b e t h e a p p l i c a t i o n o f t h i s t h e o r y o f w r e a t h p r o d u c t s % o t h e
r e p r e s e n t a t i o n t h e o r y o f s ym m e t r i c a n d a l t e r n a t i n g g r o u p s.
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 119/197
C h a p t e r I I I
A p p l i c a t i o n t o th e r e p r e s e n t a t i o n t h e o r y
o f s y m m e t r i c a n d a l t e r n a t i n g g r o u p s
T w o e x a m p l e s , t h e t h e o r y o f t h e s y m m e t r i z e d o u t e r p r o d u c t s a n d t h e
t h e o r y o f t h e g e n e r a l i z e d d e c o m p o s i t i o n n u m b e r s w i l l s h o w h o w t h e
r e p r e s e n t a t i o n t h e o r y o f w r e a t h p r o d u c t s c a n b e a pp l i e d t o t h e r e -
p r e s e n t a t i o n t h e o r y o f s y m m e t r i c a n d a l t e r n a t i n g gr o u p s .
M o r e p r e c i s e l y w e a p p l y t h e r e p r e s e n t a t i o n t h e o r y o f w r e a t h p r o -
d u c t s o f t h e f o r m G % S . I n th e f i r s t c a s e t h e u s e d s u b g r o u p s a r e
of the fo rm Sm%Sn, in the sec ond case of the fo rm Cm~S n.
A l t h o u g h t h e r e p r e s e n t a t i o n t h e o r y o f G % S h a s b e e n d e r i v e d w i t h
t h e a i d o f t h e r e p r e s e n t a t i o n t h e o r y o f t h e s y m m e t r i c g r o u p , o u r ar -
g u m e n t i s n o t c i r c u l a r s i n c e f o r t h e a p p l i e d s u b g r o u p s G ~ S ~ S
w e h a v e m < n . H e n c e t h i s a p p l i c a t i o n i s a c t u a l l y a r e c u r s i o n p r o -
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 120/197
115
t e s s . T h u s f o r e T a m p l e t h e e v a l u a t i o n o f t h e ( s t r i c t l y ) g e n e r a l i z e d
d e c o m p o s i t i o n n u m b e r s o f S i s r e d u c e d t o t h e e v a l u a t i o n of d e c o m -
p o s i t i o n n u m b e r s o f s y m m e t r i c g r o u p s o f l o w e r d e g r e e s m < n .
T h e r e a r e p r o b a b l y o t h e r w a y s o f a p p l y i n g t h i s t h e o r y o f r e p r e s e n -
t a t i o n s o f w r e a t h p r o d u c t s t o t h e t h e o r y o f t h e s y m m e t r i c g r o u p .
P r e s u m a b l y w e c a n i l l u m i n a t e i n t h i s w a y t h e c o n c e p t o f t h e s o -
c a l l e d " s t a r - d i a g r a m " o r " p - q u o t i e n t " o f a Y o u n g - d i a g r a m s a t i s f a c -
t o r i l y , b u t t h i s w i l l b e d i s c u s s e d i n t h e f o l l o w i n g p a r t s o f
t h i s p a p e r .
T h e f i r s t s e c t i o n o f t h is c h a p t e r c o n t a i n s t h e t h e o r y o f t he s y m -
m e t r i z e d o u t e r p r o d u c t s o f i r r ed u c i b l e o r d i n a r y r e p r e s e n t a t i o n s
o f s y m m e t r i c g r o u p s . T h e n a s a p r e p a r a t i o n f o r t h e t h i r d s e c t i o n
w h i c h c o n t a i n s t h e t h e o r y o f th e g e n e r a l i z e d d e c o m p o s i t i o n m a t r i x
of symm etri c and alt ern ati ng group s we s1~mmarize in the second
s e c t i o n s o m e k n o w n a n d s o m e n e w r e s u l t s a b o u t d e c o m p o s i t i o n n u m -
b e r s o f s y m m e t r i c a n d a l t e r n a t i n g g r o up s .
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 121/197
1 1 6
6 . S y m m e t r i z e d o u t e r p r o d u c t s o f i r r e d u c i b l e
C - r e p r e s e n t a t i o n s o f s y m m e t r i c g r o u p s
A c h a n c e t o a p p l y t h e r e p r e s e n t a t i o n t h e o r y o f w r e a t h p r o d u c t s t o
t h e o r d i n a r y r e p r e s e n t a t i o n t h e o r y o f t h e s y m m e t r i c g r o u p a r i s e s
nf r o m t h e t r i v i a l f a c t , t h a t t h e n o r m a l i z e r N S m n ( × S ) o f a d i r e c t
n
produ c t × S m := S m×. . . ×S m (n f a c to r s ) o f n subgro ups i somo rph ic t o
nS a n d i n S m n l i e s b e t w e e n x S a n d S m n :
n n
6 . 1 X S _< g S m n ( x S ) -< S m n •
P o r a s w e h a v e s e e n i n s e c t i o n 2 ( of . 2 . 3 3 ) t h i s n o r m a l i z e r i s a
n
f a i t h f u l pe rmu ta t i o n re p r e se n t a t i o n o f S m '~ n wi th x S m a s i t s
b a s i s g r o u p .
H e n c e t h e p r o b l e m t o d er i v e t h e r e d u c t i o n o f th e r e p r e s e n t a t i o n
n
[ a ] . . . [ ~ ] = [ ~ ] ~ . . . ~ [ ~ ] t S m n i n d u c e d f r o m × S c a n b e d i v i d e d
i n t o t wo p r o b l e m s . F o r u s i n g t h e t r a n s i t i v i t y o f t h e i n d u c i n g p r o -
c e s s a n d 6 . 1 w e o b t a i n :n
6 . 2 = f S m ( X S m ) f .
T h e f i r s t o n e o f t h e t wo r e m a i n i n g p r o b l e m s i s t o d e r i v e t h e r e -
d u c t i o n o f
n
6 . 3 [ ~ 3 ~ . . . ~ [ ~ 2 f N S m n (X S ) •
T h e s e c o n d o n e i s t h e p r o b l e m t o g i v e t h e r e d u c t i o n o f t h e r e p r e -
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 122/197
117
s e n t a t i o n s o f S m n i n d u c e d b y t h e i r r e d u c i b l e c o n s t i t u e n t s o f 6 .3 .
L e t u s f i r s t c o n s i d e r t h e r e d u c t i o n o f 6. 3.n
W e k n o w t h a t N S m ( x S ) i s a f a i t h f u l p e r m u t a t i o n r e p r e s e n t a t i o n o f
S m ~ S n , h e n c e t h e p r o b l e m i s t o gi v e t h e r e d u c t i o n o f
n
6.4 ~ [~] $ Sm~ S n •
B u t w i t h t h e r e c i p r o c i t y t h e o r e m o f P r o b e n i u s a n d 5 . 1 8 w e h a v e a t
o n c e t h e s o l u t i o n o f t h i s p r o b l e m :
n
6.5 # [~] f Sm~.S = P. fP (e ;~ ),P
i f t h e s u m i s t a k e n o v e r a l l t h e p a r t i t i o n s o f n a n d i f f P d e n o t e s
t h e d i m e n s i o n o f [ p ].
A p p l i e d t o ou r s t a r t i n g p r o b l e m w e o b t a i n f r o m 6 . 5:
n
6 . 6 ~ [ = ] f S t u n = z f P C ( ~ ; P ) f S t u n ) ,P
T h u s w e h a v e r e d u c e d t h i s p r o b l e m t o t h e r e d u c t i o n o f t he
t r i z e d o u t e r p r q d u c t s ( cf . 5 . 26 )
6 . 7 [ ~ ] ® [ ~ ] : : ( ~ ; P ) t S m n •
G a t h e r i n g u p w e o b t a i n t h e e q u a t i o n
6 ~ s [ ~ 2 . . . [ ~ ] : z f P ( [ ~ ] ® [ p ] ) ,. p
w h i c h o r i g i n a l l y d i r e c t e d t h e a t t e n t i o n t o c e r t a i n i n g e n e r a l
r e d u c i b l e r e p r e s e n t a t i o n s o f S m n w h i c h w e r e c a l l e d s y m m e t r i z e d
o u t e r p r o d u c t s . A h i n t t o c l a r i f y t h e i r t h e o r y w i t h t h e a i d o f
t h e r e p r e s e n t a t i o n t h e o r y o f w r e a t h p r o d u c t s w e o w e t o R o b i n s o n
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 123/197
1 1 8
w h o p o i n t e d o u t t h a t t h e y ar e i n d u c e d b y c e r t a i n i r r e d u c i b l e r e -
n
p r e s e n t a t i o n s o f N g m n ( x S ) ( s e e R o b i n s o n [ 3 ] , [ 4 ] , [ 5 ] , K e r b e r [ 4] ).
T o d e r i v e r e s u l t s o f t h e t h e o r y o f s y m m e t r i z e d o u t e r p r o d u c t s i t
i s u s e f u l t o d e s c r i b e t h e o r d i n a r y r e p r e s e n t a t i o n t h e o r y o f S m ~ S n
i n m o r e d e t a i l . T h i s w e s h a l l d o n o w u s i n g t h e r e s u l t s o f t he
s e c t i o n s 4 a n d 5 . B u t w e s h a l l n o t o n l y c o n s i d e r t h e i r r e d u c i b l e
r e p r e s e n t a t i o n s o f t h e f o r m ( ~ | ~ ).
P r o m t h e r e s u l t s o f t h e s e c t i o n s 4 a n d 5 w e o b t a i n , t h a t a l l t h e
i r r e d u c i b l e C - r e p r e s e n t a t i o n s o f S m ~ S n ar e o f t h e f o r m
( P ~ m ) [ ~ ] k ) ) $ S m %S n.9 P = (( ~ _[~]j) ® 'j=1 k=1
w i t h i r r e d u c i b l e C - r e p r e s e n t a t i o n s [ ~] j o f S a n d [ ~ ]k o f S n k,
i f ~ [ ~] j i s o f t y p e ( n l , . . . , n p ( m ) ) .
T h e n u m b e r o f i r r e d u c i b l e C - r e p r e s e n t a t i o n s o f S m % S n i s ( c f . 5 . 2 1) :
f ~ t Q Z P ( n l ) . . . p ( n p ( m ) ) ,( n )
i f th e s u m i s t a k e n o v e r a l l t h e p ( m ) - t u p e l s ( n) = ( n l , . . . n p ( m ) )
so that O~n i E S, Z n i = n.
W e h a v e g i v e n a n e x a m p l e f o r t he e v a l u a t i o n o f th e r e p r e s e n t i n g
m a t r i c e s i n t h e l a s t s e c t i o n .
p ( m ) p ( n ) o f t h e s e r e p r e s e n t a t i o n s 6 . 9 a r e o f t h e s p e c i a l f o r m
C ~ ) .
T h e n e x t q u e s t i o n i s, h o w w e c a n e v a l u a t e t h e c h a r a c t e r t a b l e o f
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 124/197
119
S m ~ S . O f c o u r s e w e c a n o b t a i n t h e c h a r a c t e r s b y e v a l u a t i n g t h e
m a t r i c e s f o r a c o m p l e t e s e t o f r e p r e s e n t a t i v e s o f t he c o n j u g a c y
c l a s se s u n d e r e a c h i r r e d u c i b l e o r d i n a r y r e p r e s e n t a t i o n a n d
c h e c k i n g t h e t r a c e s o f t h es e m a t r i c e s . B u t t h i s i s t h e m o s t c o m -
p l i c a t e d w a y t o g e t th e c h a r a c t e r ta b l e a nd i t c a ~ e s i m p l i f i e d
v e r y m u c h b y e v a l u a t i n g t h e m a t r i c e s o n l y f o r c e r t a i n r e p r e s e n -
t a t i o n s a n d u s i n g s y m m e t r i e s o f t h e s e t a bl e s .
T h e s e s y m m e t r i e s a r e o f t h e s am e k i n d a s t h e s e o f t h e c h a r a c t e r
t a b l e o f S w h i c h a r i s e f r o m t h e f a c t d e s c r i b e d b y 4. 1 4 f r o m w h a t
foll ows that we get the ro w of [a'] from the row of [~] by
c h a n g i n g t h e s i g n i n t h e c o l u m n s o f c o n j u g a c y c l a s s e s w h i c h b e -
l o n g t o S n ~ A .
T h e r e a s o n f o r t h e s e s y m m e t r i e s o f t h e c h a r a c t e r t a b l e o f S i s
the fact that [a] and [a'] form a pai r of irreducib le C-rep re-
s e n t a t i o n s o f S w h i c h a re a s s o c i a t e d ( i n t h e s e n s e o f C l i f f o r d ' s
t h e o r y o f r e p r e s e n t a t i o n s o f g r o u p s w i t h n o r m a l s u b g r o u p s ) w i t h
r e s p e c t t o t ~ e n o r m a l d i v i s o r A o f i n d e x 2 .
T h i s c a n b e a p p l i e d a l s o t o S m ~S n , e v e n w i t h m o r e s u c c e s s: T h e
n
n o r m a l i z e r N S m n ( × S m ), a f a it h f u l p e r m u t a t i o n r e p r e s e n t a t i o n o f
S m ~ n ~ C O n t a i n s f o r m , n >1 t w o d i f f e r e n t an d n o n t r i v i a l n o r m a l s u b -
group s of index 2, the subgr oup
6.11 Sma Sh + := Sm~S n n Am n
of the even permu tatio ns, and the subgr oup
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 125/197
1 2 0
6 . 1 2 S m ~ A n .
( P o r t h e s a k e o f s i m p l i c i t y w e w r i t e S m % S n + i n s t e a d o f ( S m % S n )+ ,
h o p i n g t h a t t h i s s u b g r o u p w i l l n o t b e c o n f u s e d w i t h S m % S ~ = S m % A n . )
S e t u s d e n o t e b y F + t h e r e p r e s e n t a t i o n a s s o c i a t e d w i t h F w i t h r e s p e c t
t o S m ~ S n + a n d b y F t h e r e p r e s e n t a t i o n a s s o c i a t e d w i t h F w i t h r e s p e c t
t o S m % A n . T h u s F + ( r e sp . p A ) m e a n s t h e i n n e r t e n s o r p r o d u c t o f P
a n d t h e a l t e r n a t i n g r e p r e s e n t a t i o n o f S m% S n w i t h r e s p e c t t o S m % S n +
( r e sp . S m ~ A n ) . I f w e d e n o t e t h e s e a l t e r n a t i n g r e p r e s e n t a t i o n s b y
A + S m % S n r e s p. A - S % S w e h a v e o b v i o u s l yA m n
A +S m~ 'gn = { ( l m ; n ) , i f m i s e v e n
6 , 1 ~ ( l m ; l n ) , i f m i s o dd
AAS m%S n = (m;1 ) .
T h u s
6 . 1 4
P+ = f P @ (Im;n) , if 2 I m
tF ® (l m;In), if 2 t m ,
F = P @ (m|1 n) .
T o d e s c r i b e F + a n d F e x p l i c i t l y i n t h e f o r m 6 . 9 w e t a k e i n t o
a c e o u n t t h a t f o r i n n e r t e n s o r p r o d u c t s t h e f o l l o w i n g i s v a l i d i f
H ~ G , D I is a r e p r e s e n t a t i o n o f H, D 2 a r e p r e s e n t a t i o n o f G :
(D 1 f G) @ D 2 = (D 1 @ (D 2 ~ H ) ) f G .
U s i n g t h i s i t i s e a s y t o v e r i f y t h e f o l l o w i n g t h e o r e m ( K e r b e r [ 4] ):
T h e i r r ed u c i b l e C - r e p r e s e n t a t i o n s o f S m ~ S n a S S o c i a t e d w i t h th e
r e p r e s e n t a t i o n 6 . 9 w i t h r e s p e c t t o S m ~ S n + r es p . S m ~ A n a r e :
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 126/197
121
~ + : = I ( ( u K ~ ' ] J ) ~ ® ( ~ [ ~ ] k ) ' ) t S m ~ S n , i f 2 1 m
(C~[~']j) @ (~[~']k) ') t Sm~S n, if 2 t m
resp.
p A : = ( ( ~ [ ~ ] j ) ® ( # l i B , ] k ) , ) 1 ~ S m ~ S n ,
i f [ a' ] j r e s p . [ ~ ' ] k d e n o t e s t h e r e p r e s e n t a t i o n a s s o c i a t e d t o, J . .
[aSj resp. [~]k wit h resp ect to A resp. An~r, i.e. if
[~'Sj := [~]j @ [ImS ' [~'S k := [~]k ® lInkS "
S p e c i a l c a s e s ar e
{ C ~ ' ; ~ ) , i f 2 I m
( ~ | ~ ) + = C ~ ' ; ~ ' ) , i f 2 ~ m ,
( a ; ~) = ( ~ ; ~ , ) .
T h i s i n d i c a t e s h o w w e c a n g e t t h e r o w s o f P + a n d p A f r o m t h e r o w
of F by chang ing the sign in cer tain collnmns.
P i s c a l l e d s e l f a s s o c i a t e d w i t h r e s p e c t t o S m a S h + ( S m ~ A ) i f F =
F + ( P = F A ) . T h e c h a r a c t e r o f s u c h a s e l f a s s o c i a t e d r e p r e s e n t a t i o n
v a n i s h e s o u t s i d e o f S m ~ S n + ( S m ~ A n) .
F i n a l l y w e m e n t i o n s p e c i a l c h a r a c t e r v a l u e s w h i c h c a n b e o b t a i n e d
b y s p e c i a l i z i n g 5 . 2 8 a n d 5 . 2 9:
6 . 1 6 I f i n 6 . 9 t h e r e p r e s e n t a t i o n ~ [ ~ ] ~ o f t h e b a s i s g r o u p i s o f
type (nl,.. .,np(m )) and if the conj ugac y class._ of ~ in S
h a s a n e m p t y i n t e r s e c t i o n w i t h S ( n ) , t h e n w e h a v e f o r t h e
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 127/197
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 128/197
1 2 3
DO ~ ~ DO 1". .3 . - ~ ~ ~ ' . ,J ,I
r ~ ~ ~ 1 ~ h ) ~ I I ~ - ~ I I
~ 1 ~ II
I ' 0
+
. --- I I , ' --
IX) I ' 0 vv v
+ +
I I I0 1 ~ 0 0 - " ~ " ~ " -~ - " ~
I !r o ~ I ' O f * o - - ' , - . x ~ . - ~
I0 r o 0 0 0 - - ' - ' ~ ~ " " - '
I I
0 - - ~ 0 0 . - ~ . . L
' '
0 0 0 I x ) D O " ~
I I I0 0 0 ~ ~ ~ - " ~
' L._ ,
0 0 0 0 0 ~ '~
v
i,,3
v
t.,o
J D
P o
v
4 ~'kT t
v
v4 ~
v
4 ~v
DO
4 ~
C ~
v
k. l r t
,#,.
U
e_Jo
O ~ m
o U"4 ,= -i -
t ~
t~ 4
m o
( 1 , 1 ; 1 )
( ( 1 2 ) , 1 ; 1 )
( ( 1 2 3 ) , 1 ; I )
( ( 1 2 ) , ( 1 2 ) ; 4 )
( ( 1 2 3 ) , ( 1 2 3 ) ; 1 )
( ( 1 2 ) , ( 1 2 3 ) ; 1 )
( 1 , 1 ; ( 1 2 ) )
( ( 1 2 3 ) , ( 1 2 3 ) ; ( 1 2 ) )
( ( 1 2 ) , ( 1 2 3 ) ; ( 1 2 ) )
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 129/197
124.
b e c o n s t r u c t e d .
I n t h e s a m e w a y w e g e t t h e z e r o s o f t h e s e c o n d , f o u r t h a n d s i x t h
c o l u m n a n d t h e f i f t h a n d s i x t h r o w. T h e b o x c o n t a i n i n g z e r o s i n
t h e r i g h t a n d l o w e r c o r n e r w e g e t f r o m 6 . 1 6 ( cf . K e r b e r E 4] ).
T h i s t a b l e h a s a l s o b e e n e v a l u a t e d b y L i t t l e w o o d ( L i t t l e w o o d [ 2] ,
p . 2 7 5 ) w i t h t h e a i d o f t h e t a b l e o f S 6 , w h i l e f o r t h i s p r o c e d u r e
t o g e t t h e t a b l e o f $ 3 ~ S 2 ( i n t h e g e n e r a l c a s e : S m ~ S n ) w e u s e d
o n l y t h e r e p r e s e n t a t i o n s o f S a n d S 2 ( r e s p . S a n d S a n d s u b -
g r o u p s o f S i n t h e g e n e r a l c a s e ) a n d n o t t h e t a b l e o f S ( r e s p .
S m n ). I n L i t t l e w o o d ' s b o o k w e c a n f i n d a l s o t h e t a b l e s o f $ 4 ~ $ 2
( p . 2 7 7 ) , $ 2 ~ S 4 ( p . 2 7 8 ) a n d $ 3 ~ S 3 ( p. 2 8 0 ) . I n a p a p e r o f R o b i n -
s o n ( R o b i n s o n E 4 ]) t h e t a b l e o f $ 2 ~ S 3 c a n b e f o u n d , h e a l s o d i d
n o t u s e t h e t a b l e o f S . I n a l a t e r p a p e r L i t t l e w o o d u s e d t h i s
m o r e d i r e c t m e t h o d , t o o ( L i t t l e w o o d L 3] ).
H a v i n g d e r i v e d t h e s e d e t a i l e d r e s u l t s o n t h e o r d i n a r y r e p r e s e n -
t a t i o n t h e o r y o f S m ~ S n w e r e t u r n t o t h e t h e o r y o f s y m m e t r i z e d
o u t e r p r o d u c t s [ ~] (~ )[ ~] o f i r r e d u c i b l e o r d i n a r y r e p r e s e n t a t i o n s
o f s y m m e t r i c g r o u p s .
A p r o b l e m w h i c h i s u p t o n o w o n l y i n c o m p l e t e l y s o l v e d i s t h e r e -
d u c t i o n o f [ a ] Q [ ~ ] ( se e t h e r e f e r e n c e s g i v e n i n R o b i n s o n [ 5] a n d
B o e r n e r [ 3 ]) . B u t u s i n g o u r t h e o r e m s w e c a n e a s i l y o b t a i n t h e
m o s t i m p o r t a n t r e s u l t s o f t h i s t h eo r y .
A t f i r s t w e g e t a t o n c e f r o m 6 . 1 5 f o r t h e m u l t i p l i c i t y
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 130/197
1 2 5
( [ a S ( ~ [ p ] , [ y ] ) o f t h e i r r e d u c i b l e r e p r e s e n t a t i o n [ y ] o f S m n i n
[ ( [ , ~ ' 2 0 [ ~ 1 , [ ~ , ' 3 ) , i f 2 I m
( [ ~ ] ® [ p ] , [ ¥ ] ) l ( E , ~ ' l O [ ~ ' ] , r ~ , ' - I ) , i f 2 1 m ,
t h e s o - c a l l e d T, t t l e w o o d ' s t h e o r e m o f c o ~ u ~ a t e s ( L i t t l e w o o d E1 ]).
A n o t h e r t h e o r e m , p e r h a p s t h e m o s t i m p o r t a n t o n e c a n a l s o b e o b -
t a i n e d e a s i l y . W i t h i t s h e l p o u r p r o b l e m c a n b e r e d u c e d t o t he
p r o b l e m t o g i v e t h e r e d u c t i o n o f s y m m e t r i z e d o u t e r p r o d u c t s o f t he
s p e c i a l f o r m [ ~ ] ( ~ [ r ] ( r _< n) . T h e a s s e r t i o n i s a n a l o g o u s t o 4 . 4 1 .
I f n = n 1 + n 2 w e d e n o t e a t f i r s t
6 .1 8 ( [ c ~ ] Q [ n l ] ) ( [ a : ] Q [ n 2 ] ) : = ( ( [ °~ ] O [ n l ] ) # ( [ ~ ] O [ n 2 ] ) ) 1 " Bm n
a n d p r o v e t h a t t h e f o l l o w i n g i s v a l i d :
6 . 19 ( [ ~ 2 Q [ n 1 2 ) ( [ ~ 2 0 [ n 2 2 ) = [ ~ 2( ~ ([ n ll [ n2 2 )
P r o o f : U s i n g a w e l l k n o w n t h e o r e m a b o ut i n d u c e d r e p r e s e n t a t i o n s
( s e e C u r t i s / R e i n e r 5 1 2 , ( 4 3 . 2 )) a n d t h e t r a n s i t i v i t y o f t h e i n -
d u c i n g p r o c e s s w e o b t a i n f o r t he l e f t h a n d s i d e , u s i n g 6 . 1 8 :
( ( a ; n l ) ~ ( ~ ; n 2 ) ) ~ 8 m ~ ( S n l X B n 2 ) ~ S m ~ 8 n t S m n •
B e c a u s e o f ( S m ~ S n l ) X ( S m ~ S n 2 ) = S m ~ ( S n l X S n 2 ) t h i s i s e q u a l t o
( ~ ; [ n l ] t l [ n 2 ] ) '~ Sm ',,,S '~ S mn = [ o ~ ] Q ( [ n l ] [ n 2 ] ) •
q . e . d .
A p p l y i n g 4 . 4 1 t o [ P 2 :
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 131/197
126
[ ~ ] = l [ ~ + j - i ] l
w e o b t a i n t h e a n n o u n c e d r e s u l t ( R o b i n s o n [ 5] , 3 . 5 3 1 ) :
F o r e x a m p l e
[ ~ ] O [ ~ ] = l [ ~ ] O [ ~ i + J - i ] l •
[ ~ ] ® [ 2 ] [ a ] ® [ 3 ][ ¢ ] 0 1 2 , 1 ] =
1 [~]~)[I]
= ( [ ~ ] O [ 2 ] ) ( [ ~ ] ® [ 1 ] ) - [ ~ ] 0 1 3 ]
= ( [ ~ ] ® [ 2 ] ) [ a ] - [ ~ ] O [ 3 ] •
[ ~ ] Q [ ~ i + J - i ] i s o ~ t he ~ o r m [ ~ ] ® [ r ] , ~ n . A n a i~ w e k n o w t he
reauctions o~ these [~] Q[~ i+J -i] we get the reauct±on o~ [~] O[ ~]
w i t h 6 . 2 0 a n d t h e L i t t l e w o o d - R i c h a r d s o n - r u l e 4 . 51 .
I t is r e m a r k a b l e t h a t w i t h t h e r e c i p r o c i t y t h e o r e m of F r o b e n i u s
w e o b t a i n
6.21 ( [ o : ] C ) [ r ] , [ y ] ) = ( [ ¥ ] ~ S m ~ S r ,@ [ a ]) ,
w h i c h r e d u c e s t h e p r o b l e m t o t he e v a l u a t i o n o f t h e c h a r a c t e r o f
@[~] (cf. Kerber [4]).
C o n c l u d i n g t h i s s e c t i o n we w o u l d l i k e t o d e r i v e t w o e q u a t i o n s c o n -
c e r n i n g t h e m a t r i x
6.22
o f t h e m u l t i p l i c i t i e s
6.23 r ~
for a fixed pa rtit ion ~ of m and for the part itio ns ~ of n, y of
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 132/197
127
m n . T h u s R a i s a p ( m m ) x p ( n ) - m a t r i x .
L e t [ 6 ] b e a n i r r e d u c i b l e r e p r e s e n t a t i o n o f S n _ I an d
6 . 24 r ~ := ( [ ~ ] ~ [ 6 ] , [ E ] ) •
U s i n g t h e L i t t l e w o o d - R i c h a r d s o n - r u l e 4 .5 1 w e g e t a t o n c e t h e m a t r i -
c e s S : = ( s ~ ) a n d E
6.25
a n d
6.26 e~6
A sp ecia l c~se of 6.19 is
: = ( e ~& ) , w h o s e e n t r i e s a r e d e f i n e d b y
s ~ : : ( [ E ] [ = ] , [ ~ ] )yE
- - ( [ 6 ] [ i ] , [ ~ ] ) .
6 . 2 7 ( [ = ] 0 1 6 ] ) [ = ] -- [ = ] ® ( [ 6 ] [ i ] )
W e c a n c o m p a r e t h e m u l t i p l i c i t i e s o f t he i r r e d u c i b l e c o n s t i t u e n t s
o n b o t h s i d e s o f 6 . 2 7 .
F o r t h e l e f t h a n d s i d e w e o b t a i n f r o m 6 . 2 4 a n d 6 . 2 5:
6 . 2 8 ( [ ~ ] Q [ 6 ] ) [ = ] = ~ r a~ [ a] = n s v E r E 6 [ V ] -t o £ ~ y
A n d s i n c e 6 . 2 6 i s v a l i d t h e r i g h t h a n d s i d e o f 6 . 27 i s
6.29 [ = ] Q ( [ ~ ] [ 1 ] ) = n e ~ [ = ] Q [ ~ ] = ~ , r ~ e ~ 6 [ ~ ] •~,~
C o m p a r i n g 6 . 2 8 a n d 6 . 2 9 w e o b t a i n "
6 . 5 0 R ~ = S ~ R *
( R o b i n s o n [ 5] , 3 . 5 48 ) a s a n e c e s s a r y c o n d i t i o n f o r t h e w a n t e d
m a t r i x R m .
A s e c o n d c o n d i t i o n f o r R ~ c a n b e d e r i v e d u s i n g t h e t h e o r e m 6 . 1 6
c o n c e r n i n g t h e c h a r a c t e r s o f t h e i r r e d uc i b l e r e p r e s e n t a t i o n s o f
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 133/197
128
S m ~ S n -
W e
c o n s i d e r t h e e q u a t i o n 6 . 2 3 . U s i n g t h e r e c i p r o c i t y t h e o r e m o f
F r o b e n i u s w e o b t a i n
6 .3 S m , S n = + . . . ,
i f w e g a t h e r u n d e r t h e s n m m a t i o n s i g n e x a c t l y t h o s e i r r e d u c i b l e
c o n s t i t u e n t s o f [ y ] ~ S m a S h , w h i c h a r e o f t h e f o r m ( ~ ;~ ) . S i n c e
6 . 1 6 i t s u f f i c e s t o r e g a r d o n l y t h e s e c o n s t i t u e n t s o f th e f o r m
( ~ ; ~) i f w e t a k e t h e c h a r a c t e r o f ( e ; ( 1 . . . n ) ) o n b o t h s i d e s o f
t h i s e q u a t i o n . W e o b t a i n
C¥(n ) = ~ r ~ ; ~ ( e ; ( 1 . . . n ) ) .
( T h e p a r t i t i o n o f ( e ; ( 1 . . . n ) ) i s P ( e ; ( 1 . . . n ) ) = ( n , . . . , n ) = ( n m ) . ) .
U s i n g 6 . 1 6 w e g e t t h e r e f r o m :
6.~2 C =(n )
k r ~ 6 f ~ ( - 1 ) k
~ , ~ : # = ( n - k , 1 )
a s a s e c o n d n e c e s s a r y c o n d i t i o n f o r t h e c o e f f i c i e n t s r ~ of the
w a n t e d m a t r i x R ~ ( s e e K e r b e r [ 4] ).
A t t h e e n d o f t h i s s e c t i o n w e g i v e t h r e e o f t h e m o s t i m p o r t a n t
r u l e s f o r t h e s e s y m m e t r i z e d o u t e r p r o d uc t s . T h e y a r e w e l l k n o w n
b u t n o w w e c a n o b t a i n t h e s e r u l e s m u c h m o r e d i r e c t l y w i t h t h e a id
o f t h e r e p r e s e n t a t i o n t h e o r y o f w r e a t h p r o d u c t s .
A g e n e r a l i z a t i o n o f 6 . 1 9 i s
( [ ~ ] O [ ~ ] ) ( [ ~ ] Q [ ~ ] ) = [ ~ ] o ( [ ~ ] [ ~ ] ) ,
t h e p r o o f i s q u i t e a n a l o g o u s t o t h e p r o o f o f 6 . 1 9 .
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 134/197
129
A s p e c i a l c a s e o f 5 . 2 7 i s
6 . 3 4[ ~ ] ® ( [ ~ ] + [ ¥ D = [ ~ ] ® [ ~ ] ÷ [ , , ] 0 [ ~ , 1 ,
a n d f r o m t h e a s s o c i a t i v i t y o f th e w r e a t h p r o d u c t m u l t i p l i c a t i o n
w e o b t a i n
( E a ] ® C ~ l ) ® 1 " ~ ,3 --- [ a ] ® ( C # ' l ® [ ~ , l ) .
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 135/197
1 30
7 . B l o c k - s t r u c t u r e a n d d e c o m p o s i t i o n n u m b e r s
o f s y m m e t r i c a n d a l t e r n a t i n g g r o u p sI - , ' " i l l i l
T h e d e v e l o p m e n t o f t h e m o d u l a r r e p r e s e n t a t i o n t h e o r y o f t h e s y m -
m e t r i c g r o u p b e g a n i n 1 9 4 0 w i t h t h e p u b l i c a t i o n o f t h e t wo p a r t s
o f T . N a k a y a m a ' s p a p e r " O n s o m e m o d u l a r p r o p e r t i e s o f i r r e d u c i b l e
r e p r e s e n t a t i o n s o f s y m m e t r i c g r o u p s " ( N a k a y a m a [ I ] , [ 2 ] ). T h e s e c o n d
p a r t o f t h i s p a p e r c o n c l u d e s w i t h a c o n j e c t u r e a b o u t t h e p - b l o c k -
s t r u c t u r e o f t h e s y m m e t r i c g r o u p w h i c h h a s b e e n p r o v e d f i r s t b y
B r a u e r a n d R o b i n s o n i n 1 94 7 ( B r a u e r [ I] , R o b i n s o n [ 2] ) a n d w h i c h
i s t h e f o u n d a t i o n f o r a l l t h e f o l l o w i n g p a p e r s c o n c e r n i n g t h i s
theory.
B e y o n d t h i s f u n d a m e n ta l t h e o r e m w h i c h i s s t i ll c a l l e d " N a k a y a ma ' s
c o n j e c t u r e " w e k n o w a l o t o f r e s u l t s b u t n o t t h e w a n t e d g e n e r a l
r e s u l t s ( i. e. i n d e p e n d e n t o f n a n d p ) a b o u t t h e d e c o m p o s i t i o n
n u m b e r s o f S w i t h r e s p e c t t o p . P u r t h e r m o r e w e k n o w h o w t h e
e v a l u a t i o n o f t h e g e n e r a l i z e d d e c o m p o s i t i o n n u m b e r s C a n b e r ed u c e d
t o t h e e v a l u a t i o n o f d e c o m p o s i t i o n n u m b e r s o f s y m m e t r i c g r o u p s o f
l o w e r d e g r e e s a n d w e k n o w s o m e a n a l o g o u s t h e o r e m s a b o u t t h e a l t e r -
n a t i n g g ro u p , e . g . w e k n o w t h e b l o c k - s t r u c t u r e o f A a n d h o w w e
c a n g e t t h e d e c o m p o s i t i o n m a t r i x o f A a s f a r a s th e d e c o m p o s i t i o n
m a t r i x of S i s k n o w n .
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 136/197
131
W e w o u l d l i k e t o d e s c r i b e s o m e o f t h e se n e w e r r e s u l t s b e g i n n i n g
w i t h t h e t h e o r e m a b o u t t h e b l o c k - s t r u c t u r e o f A n • W e s h a l l d e s -
c r i b e t h e p r e s e n t s i t u a t i o n o f t h e t h e o r y o f d e c o m p o s i t i o n n u m -
b e r s o f s y m m e t r i c a n d a l t e r n a t i n g g r o u p s •
T o f o r m u l a t e N a k a y a m a ' s c o n j e c t u r e w e n ee d t h e f o l l o w i n g d e f i -
n i t i o n :
7 .1 D e f . : L e t [ a~ b e a Y o u n g - d i a g r a m a n d q a n a t u r a l n u m b e r .
I f w e c a n c e l s u c c e s s i v e l y p a r t s o f t h e r i m w h i c h b e l o n g
t o h o o k s o f l e n g t h q , t h e n a ( u n i q u e l y d e t e r m i n e d ) s u b -
d i a g r a m [ ~] r e m a i n s w h i c h w e c a l l t h e q - c o r e o f [ u] .
P o r e x a m p l e i f q = 3:
i •
po p pl
/
• • / / /• , r j I". -. ~ [ 3 2 , 2 , 1 ] = [ 0 1 •
I f p i s a p r i m e n u m b e r , t h e n t h e f u n d a m e n t a l t h e o r e m o f t h e m o d u -
l a r r e p r e s e n t a t i o n t h e o r y o f t h e s .y mm et ri c g r o u p r e a d s a s f o l l o w s :
~ 2 ( " N a k a 2 a m a ' s c o n j e c t u r e , ' )
T h e i r r e d u c i b l e o r d i n a r y r e p r e s e n t a t i o n s o f S w h i c h f o r m t h e
p - b l o c k o f S t o w h i c h r a~ b e l o n g s a r e e x a c t l y t h e r e p r e s e n -
t a t i o n s E ~ o f S w i t h t h e s a m e p - c o r e a s [~ ], i . e . t h e r ~]
w i t h
-- •
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 137/197
132
A s h a s b e e n s a i d a b o v e : t h i s i s n o l o n g e r a c o n j e c t u r e , s i n c e t h i s
t h e o r e m h a s b e e n p r o v e d i n 1 9 4 7 b y B r a u e r a n d R o b i n s o n !
T o p r o v e 7 .2 t h e w e l l k n o w n c h a r a c t e r i z a t i o n o f t h e p - b l o c k s b y
t h e c l a s s m u l t i p l i e r s ( s e e C u r t i s / R e i n e r [ I] , 8 5 , 8 6) c a n b e u s e d :
[ ~ ] a n d [ ~ ] b e l o n g t o t h e s a m e p - b l o c k i f a n d o n l y i f t h e i r c h a r a c -
t e ~ a , ~ s a t i s f y t h e f o l l o w i n g c o n g r u e nc e m o d u l o p :
7 3 : = (Loal/f ) (ic iIf ) =: mod p,
o n a l l t h e c o n j u g a c y c l a s s e s C o f S .
A n i m p o r t a n t r o l e i n t h e p r o o f i s p l a y e d b y t h e d e f e c t o f a b l o c k .
I t t u r n s o u t, t h a t t h e d e f e c t d o f t h e b l o c k c o n t a i n i n g [ ~] a n d
t h e n u m b e r b o f p - h o o k s w h i c h c a n b e r e m o v e d f r o m [ ~] t o y i e l d
[ ~ ] s a t i s f y t h e e q u a t i o n
d : b + ep(b~ !)
i f a s in s e c t i o n I e p (m ) d e n o t e s t h e e x p o n e n t o f t he m a x i m a l p o w e r
o f p w h i c h d i v i d e s m . b ~ i s c a l l e d t h e p - w e i g h t o f [ a ].
A c t u a l l y t h e f o l l o w i n g i s v a l i d ( B r a u e r [ 1] ):
~ . 5 T h e d e f e c t g r o u p o f t h e b l o c k o f [ ~] i s i s o m o r p h i c t o a p
p-Sylow-subgroup__ of Cp ~Sb a -< Spb~, i.e. iso mor phi c to the
w r e a t h p r o d u c t C p ~ P b ~ , i f P b a d e n o t e s a p - S y l o w - s u b g r o u p o f
S b ~ "
T h i s p r o v i d e s a n o p p o r t u n i t y t o a p p l y t h e t h e o r y o f r e p r e s e n t a t i o n s
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 138/197
133
o f w r e a t h p r o d uc t s . A c t u a l l y s o m e p a rt s o f t he k n o w n p r o o f s o f
N a k a y a m a ' s c o n j e c t u r e c a n b e s i m p l i f i e d i n t h i s w a y . B u t t h i s r e -
m a r k m a y s u f f i c e h er e , a m o r e d e t a i l e d d i s c u s s i o n i s l e f t t o t h e
l a t e r p a r t s o f t h i s p a p e r , s i n c e w e s h a l l h a v e a s i m i l a r a p p l i -
c a t i o n to t he t h e o r y o f g e n e r a l i z e d d e c o m p o s i t i o n n u m b e r s w h i c h
w i l l b e d i s c u s s e d i n f u l l d e t a i l .
B e f o r e d o i n g t h i s w e w o u l d l i k e t o c o n s i d e r t h e a l t e r n a t i n g g r o u p .
T h e t h e o r e m c o n c e r n i n g a l t e r n a t i n g g r o u p s a n d a n a l o g o us t o N a k a -
y a m a ' s c o n j e c t u r e i s ( P u t t a s w a m a ia h [ 1 ] , P u t t a s w a m a i a h / R o b i n s o n
[1], Ke rb er [3]):
7,6 (i) If [a] = [~], then every ir reduc ible cons titu ent of [ulnA
f o r m s i t s o w n p - b l o c k an d e a c h m o d u l a r r e p r e s e n t a t i o n a s -
s o c i a t e d w i t h s u c h a c o n s t i t u e n t i s i r r e d u c i b l e .
( i i ) I f [ ~] ~ [ ~ ], t h e n t o th e p - b l o c k o f a n i r r e d u c i b l e c o n -
s t i t u e n t o f [ ~] $ A b e l o n g e x a c t l y t h e i r r e d u c i b l e c o n -
s t i t u e n t s o f r e s t r i c t i o n s [ ~] $ A o f s u c h r e p r e s e n t a t i o n s
[~] of S for whi ch
P r o o f : W e s h a l l r e p e a t e d l y u s e t h e t h e o r e m ( o f. C u r t i s / R e i n e r [ 1 ] ,
( 8 6 . 3 )) t h at a n o r d i n a r y i r r e d u c i b l e r e p r e s e n t a t i o n f o r m s i t s
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 139/197
134
o w n p - b l o c k a n d i s m o d u l a r i r r e d u c i b l e i f p is c o n t a i n e d i n i t s
d i m e n s i o n a s o f t e n a s i n t h e o r d e r o f th e g r o u p .
( i ) W e a s s u m e f i r s t , t h a t [ ~ ] = [ ~ ] .
a ) I f ~ $ a ' , t h e n ( c f . # . 5 4 ) [ ~ ] ~ A n i s i r r e d u c i b l e .
[ a ] = [ ~ ] i m p l i e s , t h a t [ a ] c o n t a i n s n o h o o k o f l e n g t h p , h e n c e
i n t h i s c a s e ( c f. 4 . 4 6 ) :
e p ( f [ a ] ~ A n ) = e p ( f u ) = e p ( n ! ) ~ e p ( n ! / 2 ) = e p ( J A n J ) , i f n > 1 .
U s i n g t h e t h e o r e m m e n t i o n e d a b o v e , t h i s p a r t o f t h e s t a t e m e n t
i s p r o v e d f o r t h e c a s e [ ~ ] = [ ~ ] ~ [ a ' ] .
b ) I f o n t h e c o n t r a r y ~ = a ', t h e n b y 4 . 5 4 t h e r e s t r i c t i o n d e c o m -
poses:
[ a ] ~ A n = [ = ] + + [ a ] - ,
a n d [ a] a r e i r r e d u c i b l e o r d i n a r y r e p r e s e n t a t i o n s o f d i m e n s i o n
f a / 2 . [ a ] = [ ~ ] i m p l i e s a g a i n e p ( n ! ) = e p ( f a ) . T h u s
e p ( f ~ -+ ) = e p ( f a / 2 ) = e p ( n ! / 2 ) = e p ( l A n l ) ,
a n d t h e s t a t e m e n t i s p r o v e d f o r t h e c a s e [ i f ] = [ ~ ] = [ ~ ' ] .
( i i ) W e a ss um e n o w t h a t [ ~ 3 + [ ~ ] .
a ) A t f i r s t w e w o u l d l i k e t o s h o w t h a t u n d e r t h e a d d i t i o n a l
a s s u m p t i o n p ~ 2 t h e r e s t r i c t i o n [ a] ~ A c a n n o t c o n t a i n a n
i r r e d u c i b l e c o n s t i t u e n t w h i c h b e l o n g s t o a b l o c k o f d e f e c t 0.
I f f a A d e n o t e s t h e d i m e n s i o n o f s u c h a s u p p o s e d c o n s t i t u e n t o f
a b l o c k o f d e f e c t 0 , w e h a v e
e p ( f a A ) = e p ( n ! / 2 ) = e p ( n ! ) ,
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 140/197
1 3 5
t h e l a s t e q u a t i o n i s v a l i d s i n c e w e h a v e a s s u m e d p + 2.
B e c a u s e o f f a A = f a o r =f a / 2
t h i s i m p l i e s
e p C n ! ) = e p ( f a A ) = e p ( f a ) ,
i n c o n t r a d i c t i o n t o Ca ] ~ [~ ] .
b ) I f p = 2 w e h a v e f o r t h e d i m e n s i o n o f a c o n s t i t u e n t [ a ] A o f
C a] $ A w h i c h b e l o n g s t o a b l o c k o f d e f e c t 0 a n d w h i c h i s
t h e r e f o r e m o d u l a r i r r e d u c i bl e :
e 2 ( f a A ) = e 2 ( n ! / 2 ) = s 2 ( n X ) - 1 . ( 1 )
a AW i t h e 2 ( f a ) ~ e 2 ( f ) w e o b t a i n
e 2 ( f a ) = e 2 ( n ! ) - I ( 2 )
s i n c e [ a ] + [ ~ ] .
C o m p a r i n g ( I) a n d ( 2) w e g e t
e 2 C f a A ) = e 2 ( f a ) ,
a A f ~ = f a / 2 w e o b t a i nu c h t h a t b e c a u s e o f f = o r
[ a ] ~ A = [ a ] A •
S i n c e on a c c o u m t o f ( 2) C a] c o n t a i n s e x a c t l y o n e 2 - h o o k , C a ] b e -
l o n g s t o a 2 - b l o c k c o r r e s p o n d i n g t o a 2 - c o r e w i t h n - 2 n o d es .
2 - c o r e s a r e s e l f a s s o c i a t e d : C ~] = [ ~ ] f o r e v e r y 2 - c o r e s i n c e
f o r e v e r y 2 - c o r e [ ~] w e h a v e
= C o l o r = l j
H e n c e t h e d i a g r a m C a ] c o n t a i n i n g e x a c t l y o n e 2 - h o o k i s o f o n e
o f t h e t w o f o l l o w i n g f o r m s :
C a ] = [ ~ 1 . 2 , ~ 1 - 1 , . . . , 2 , 1 J o r C a ] = 1 , a 1 - 1 , . . . , 2 , 1 3 ] •
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 141/197
1 36
T h e s e t w o r e p r e s e n t a t i o n s a r e a s s o c i a t e d w i t h r e s p e c t t o A n , a n d
t h e i r r e s t r i c t i o n s t o A a r e e q u a l . H e n c e o n l y o n e o f t h e m
y i e l d s a r o w o f t h e d e c o m p o s i t i o n m a t r i x o f A . T h u s [ ~ ] A f o r m s
i t s o w n b l o c k a n d t h i s b l o c k c o n s i s t s a c t u a l l y o f t h e c o n s t i -
t u e n t s o f r e s t r i c t i o n s [ ~3 ~ A w i t h [ ~ ] = [ ~] o r [ ~3 = [ ~ ']
s i n c e t h e l a s t c o n s i d e r a t i o n s h o w s t h a t t h e r e i s u p t o e q u i v a -
l e n c e o n l y o ne s u c h c o n s t i t u e n t :
[ m ] A = [ ~ I + 2 ' $ I - I ' ' ' ' ' 2 ' I ] $ A n = K SI 'S I - I ' ' ' ' ' 2 ' 1 3 ] $ A n "
T h u s t h e s t a t e m e n t i s p r o v e d i n c a s e t h a t [ ~] $ E ~] a n d [ ~ ] ~ A n
c o n t a i n s a c o n s t i t u e n t o f a b l o c k o f d e f e c t 0 a n d i f [ ~ ] $ K ~ ]
t h i s i s o n l y t h e c a s e i f p = 2 .
c ) N o w l e t [ ~ ] A b e a n i r r e d u c i b l e c o n s t i t u e n t o f [~ ] $ A s o t h a t
= o r =
a ) a n d b ) i m p l y t h a t w e c a n a s s u m e t h a t [ ~ ] A a n d t h e c o n s t i -
t u e n t s [ ~ ] A o f [~ 3 ~ A b e l o n g t o b l o c k s w i t h d e f e c t s > 0. W e
h a v e t o s h o w t h a t [ ~ ] A a nd [ ~ ] A b e l o n g t o th e s a m e b l o c k . T o
p r o v e t h i s w e u s e t h e c l a s s m u l t i p l i e r s .
S i n c e [ ~] b e l o n g s t o t h e S n - b l o c k o f [ ~ ] o r o f [ ~' 3 w e h a v e
( C u r t i s / R e i n e r I s] , ( 8 5 . 1 2 )) :
f o r a l l t h e p - r e g u l a r S n - c l a s s e s C w h i c h s a t i s f y C ~ A n -
W e w o u l d l i k e t o s h o w th e v a l i d i t y o f t h e a n a l o g o u s c o n g r u e n c e s
~ A ~ A ,f o r ~ a n d t h i s w o u l d c o m p l e t e t h e p r o o f o f t h i s p a r t o f
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 142/197
137
o u r s t a t e m e n t ( s ee C u r t i s / R e i n e r [ I ] , ( 8 6 . 1 9 ) ) .
= A ~ A
T h e t h e o r e m of P r o b e n i u s ( 4 .5 5 ) i m p l i e s t h a t ~ r e s p .
a g r e e w i t h C r e s p . C ~ o r w i t h ~ C ~ r e s p . ½ C ~ o n n o n - s p l i t t i n g
c l a s s e s o f S . T h e s a m e i s v a l i d f o r t h e d i m e n s i o n s , h e n c e f o r
s u c h n o n - s p l i t t i n g c l a s se s c a _ c A n w e h a v e a l s o
~ A 8 AW a ~ ® a ( P ) "
T h e e l e m e n t s o f s p l i t t i n g c l a s s e s c o n s i s t o f c y c l e s o f p a i r w i s e
d i f f e r e n t l e n g t h s ( s ee 1 . 23 ) . H e n c e t h e o r d e r o f t h e c e n t r a l i -
z e r o f a p e r m u t a t i o n w h i c h b e l o n g s t o a s p l i t t i n g c l a s s i s t h e
p r o d u c t o f it s c y c l e l e n g t h s ( s ee 2 . 3 2 ). I f s u c h a p e r m u t a t i o n
i s a p - r e g u l a r o n e, p d o e s n o t d i v i d e a n y o n e o f t h e s e c y c l e
l e n g t h s a n d t h e r e f o r e p d o e s n ' t d i v i d e t h e o r d e r o f t h e c e n t r a -
l i z e r s u c h t h a t th e d e f e c t o f s u c h a p - r e g u l a r s p l i t t i n g c l a s s
i s O . H e n c e f r o m a w e l l k n o w n t h e o r e m ( C u r t i s / R e i n e r [ I] ,
( 8 6 . 2 7 ) ) w e g e t :
~ A ~ A® a ~ 0 m ® a ( P )
f o r a l l t h e p - r e g u l a r s p l i t t i n g c l a s s e s , s i n c e [ ~ ] A a n d [ ~ ] A
b e l o n g t o b l o c k s o f d e f e c t s > 0.
T h u s fo r a l l t h e p - r e g u l a r A n - c l a s s e s C w e h a v e
~ A ~ A® a ~ ~ a ( P ) '
h e n c e E ~ S A a n d [ ~ J A b e l o n g t o t he s a m e b l o c k .
d ) I t r e m a i n s t o sh o w , t h a t t h e b l o c k o f [ ~ ] A d o e s n o t c o n t a i n a
c o n s t i t u e n t [ ~ ] A o f a r e p r e s e n t a t i o n [ ~] ~ A w i t h [ ~] + [ ~]
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 143/197
138
a n d +
T h e o r d i na r y i r r e d u c i b l e r e p r e s e n t a t i o n s b e l o n g i n g t o a c e r t a i n
b l o c k B c a n b e c h a r a c t e r i z e d a s f o l l o w s : t w o o r d i n a r y i r r e d u -
c i b l e r e p r e s e n t a t i o n s b e l o n g t o B i f a n d o n l y if t h e r e e x i s t s
a c h a i n of o r d i n a r y i r r e d u c i b l e r e p r e s e n t a t i o n s b e g i n n i n g w i t h
o n e of t h e t w o r e p r e s e n t a t i o n s a n d e n d i n g w i t h t h e o t h e r o n e
a n d so t ha t m o d u l a r r e p r e s e n t a t i o n s a s s o c i a t e d t o a n y tw o
n e i g h b o u r s o f t h e c h a i n h a v e a n i r r e d u c i b l e c o n s t i t u e n t i n
c o m m o n .
H e n c e i t s u f f i c e s t o s h o w t h a t m o d u l a r r e p r e s e n t a t i o n s [ ~ ] A
a n d [ 8 ]A a s s o c i a t e d w i t h i r r e d u c i b l e c o n s t i t u e n t s [ ~ ] A a n d [ ~ ]A
of [~] 4 A n and [8] $ A n suc h that [~] + [S] and [~] + [S']
h a v e n o i r r e d u c i b l e c o n s t i t u e n t i n c o m m o n .
P r o m C l i f f or d ' s t h e o r y o f r e p r e s e n t a t i o n s o f g r o u p s w i t h
n o r m a l d i v i s o r s w e g e t t h a t a n i r r e d u c i b l e m o d u l a r c o n s t i t u e n t
P ~ o f [ ~ ] ~ A n i s a c o n s t i t u e n t o f t h e r e s t r i c t i o n P ~ ~ A o f
a m o d u l a r i r r e d u c i b l e r e p r e s e n t a t i o n F ~ b e l o n g i n g e i t h e r to
t h e p - b l o c k o f S w i t h p - c o r e [ ~] o r t o t h e a s s o c i a t e d p - b l o c k
w i t h p - c o r e I S '] . B u t [ 8 ] i s n o t c o n t a i n e d i n o n e o f t h e s e t w o
b l o c k s o f S .
I f n o w
~ d i k F k[~] k
d e s c r i b e s t h e m o d u l a r d e c o m p o s i t i o n o f [ ~] , t he n [ ~ ] ~ A h a s
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 144/197
139
t h e s a m e d e c o m p o s i t i o n a s t h e r e s t r i c t i o n o f t h e m o d u l a r r e p r e -
s e n t a t i o n o n t h e r i g h t h a n d s i d e :
A n = d i k ( A n )k
T h u s t h e m o d u l a r d e c o m p o s i t i o n o f t h i s r i g h t h a n d s i d e c o n t a i n s
t h e d e c o m p o s i t i o n o f [ ~ ] A. B u t s i n c e [ U ] A is c o n t a i n e d i n q u i t e
a n o t h e r b lo c k , t h i s r i g h t h a n d s i d e a n d h e n c e t h e d e c o m p o s i t i o n
i i , i i
o f [ ~ ] A' t o o , c a n n o t c o n t a i n a m o d u l a r r e p r e s e n t a t i o n i n c o m m o n
with [~]A"
q.e.d.
7 . 2 a n d 7 . 6 e n a b l e u s t o e v a l u a t e t h e d i s t r i b u t i o n o f t h e o r d i n a r y
i r r e d u c i b l e r e p r e s e n t a t i o n s o f S a n d A i n t o p - b l o c k s i n a v e r y
s i m p l e w a y a n d f o r e v e r y n a n d p.
B u t t h e p r o b l e m o f f i n d i n g t h e d e c o m p o s i t i o n n u m b e r s i s s t i l l f a r
f r o m a s a t i s f a c t o r y s o l u t i o n . W e w o u l d l i k e t o d e s c r i b e t h i s n ow .
W e s h a l l t r e a t t h e c a s e p = 2 a n d r e p o r t u p o n t h e k n o w n r e s u l t s .
T h e r e a f t e r w e s h a l l d i s c u s s w h a t c a n b e s a i d a b o u t t h e d e c o m p o ~
s i t i o n m a t r i x o f A n i f t h e d e c o m p o s i t i o n m a t r i x o f S i s k n o w n .
In certain cases, for examp le if n~2p, it is easy to get the de-
c o m p o s i t i o n n u m b e r s o f S ( s ee R o b i n s o n [ 5] , P . 12 2 ). B u t f o r t h e
g e n e r a l c a s e, t h e r e i s o n l y th e m e t h o d o f e x p l i c i t l y r e d u c i n g t h e
r e p r e s e n t i n g m a t r i c e s w h i c h i s p o s s ib l e w i t h o u t a v a s t a m o u n t o f
c a l c u l a t i o n s o n l y f o r v e r y s m a l l d i m e n s i o n s ( s e e R o b i n s o n [ 5 ]) -
T h e u s e o f a n i n d u c t i o n p r o c e s s s e e m s t o be m u c h m o r e p r o m i s i n g .
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 145/197
1 4 0
A s w e s o o n s h a l l s e e s u c h a p r o c e s s t o g e t h e r w i t h s o m e r e s u l t s o n
t h e d e c o m p o s i t i o n n u m b e r s o f s p e c i a l r e p r e s e n t a t i o n s a l l o w s t he
e v a l u a t i o n o f t h e d e c o m p o s i t i o n n u m b e r s o f S w i t h r e s p e c t t o p = 2
u p t o n = 9 . W e w o u l d l i k e t o s h o w h o w t h i s c a n b e d o n e .
P e r a f i x e d p r i m e n u m b e r p l e t
I = (d~k)I := Dn, p
d e n o t e t h e d e c o m p o s i t i o n m a t r i x o f S w i t h r e s p e c t t o p . ( Th e u p p e r
i n d e x I w i l l b e s h o w n t o b e o f u s e i n t h e f o l l o w i n g s e c t i o n w h e r e
t h e g e n e r a l i z e d d e c o m p o s i t i o n m a t r i x w i l l b e c o n s i d e r e d w h o s e f i r s t
c ol ,, m~ s a r e b u i l t u p b y D I . )
I f t h e o r d i n a r y i r r e d u c i b l e r e p r e s e n t a t i o n [ a ] i o f s b e l o n g s t o
t h e i - t h r o w o f D I i . e . i f
I F ~ ,[ ~ ] i ~ Z d i k
k
t h e m o d u l a r d e c o m p o s i t i o n o f Z d ~ k [ a] i is t h e s a m e a s t h e d e c o m -
i
p o s i t i o n o f t h e k - t h p r i n c i p a l i n d e e o m p o s a b l e U o f S n:
1 7 j.7 U ~ Z di k [ ]i "i
T h e i n d u c e d r e p r e s e n t a t i o n U k ~ S n + I is a d i r e c t s u m o f p r i n c i p a l
I ) h a s t h e s a m e d e -i n d e c o m p o s a b l e s o f S n + 1 , h e n c e Z d i k ( [ ~ ] i $ S n + Ii
c o m p o s i t i o n a s a c e r t a i n s u m of p r i n c i p a l i n d e o o m p o s a b l e s S j o f
S n + 1 :
[ ~ ] i ~ Z a j ~ j .. 8 Z d i k ( S n + 1 )i j
T h e b r a n c h i n g t h e o r e m 4 . 5 2 i mp l i es , t h a t t h e i r r e d u ci b l e c o n s t i t u -
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 146/197
141
e n t s o f [ ~ ] i t S n +l a r e e x a c t l y t h e [ ~] a r i s i n g f r o m [ ~ ] i b y a d d i n g
o n e no d e . R e s t r i c t i n g t h e s e a d d i t i o n s i n s u c h a w a y t h a t t h e
a r i s i n g d i a g r a m s [ #] h a v e t h e s a m e p - c o r e , w e c a n a s s u r e , t h a t t h e
d e c o m p o s i t i o n o f t h e a r i s i n g r e p r e s e n t a t i o n o f Sn + 1 co n t a i n s p r i n -
c i p a l i n d e c o m p o s a b l e s b e l o n g i n g t o o n e b l o c k o n l y.
T h e n o d e i n t h e i - t h r o w a n d j - t h c o l u m n o f [ 6] i s
c a l l e d a n r - n o d e ( w i t h r e s p e c t t o p ) i f
j - i ~ r (p) .
By
r
[ 6 ] t S n + l
w e s h a l l d e n o t e t h e r e p r e s e n t a t i o n r - i n d u c e d b y [ 6] a n d
c o n s i s t i n g e x a c t l y o f t h e r e p r e s e n t a t i o n s [ #] ( e ac h w i t h
m u l t i p l i c i t y 1) o f S n + I w h o s e d i a g r a m s a r i s e f r o m [ ~] b y
a d d i n g a n r - n o d e .
A n a l o g o u s l y w e d e f i n e t h e r - r e s t r i c t i o n o f E ~] t o S n _ I
a n d c a l l t h e p r o c e d u r e t h e r - i n d u c i n 6 r e s p . r - r e s t r i o t i n 6
p r o c e s s .
U s i n g N a k a y a m a ' s c o n j e c t u r e w e o b t a i n t ha t t he c o n s t i t u e n ts o f
r[ 6 ] ~ S n+ 1 h a v e t h e s a m e p - c o r e s o t h a t t h e y a l l b e l o n g t o t h e
s a m e p - b l o c k o f S n ÷ I a n d t h a t a l l t h e d i a g r a m s w i t h t h i s p - c o r e
r
a n d o u t o f [ 6 ] t S n + I a r e c o n t a i n e d i n [ a] ~ S n + 1 . H e n c e w e h a v e
( s e e R o b i n s o n C 5 ] , 6 . 1 1 ):
7 . 1 0 I f [ ~ ] a n d [ y ] a r i s e f ro m [ 6 ] b y a d d i n g a n o d e , th e n [ ~ ] = [ ~ ]
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 147/197
1 4 2
if and only if the added nodes are of the same residue class
r modulo p.
This impl ies for the decomposit ion matrix:
7,11
r~ ~
z ~ k ( [ a ] i f S n + 1 ) = z b s U S ,± j
such that the U~ wi th b~ $ 0 belon g to the same block of Sn+ 1.. , - - _ _
With this fu mdament al result we can start wit h our example p = 2.
The only princip al indecomposa ble of S I is [1], this is trivial.
The resi due class modulo 2 of the only node of the diagram [I] is
O. Thus
0 o 1 1
U 1 ~ S2 = [ 1 ] $ S 2 = ~ , [ 1 ] t S 2 = [ 2 ] + [ 1 2 ] ~ U 1 t S "
S 2 is a 2-group, h ence it possesses only one princ ipal indecompo-
sable and the last e quation toget her wit h 7.11 implies that this
principa l inde composable has the same decompositio n as [2] + [ 1 ~ .
T h u s
2 = [ 1 2 ]
is the decomp ositio n ma trix of S 2 for p = 2.
To proceed with the r-induci ng process we replace the nodes of
the diag ram by their residue classes modulo 2:
0[ 2 ] : 0 1 [ 1 2 ] : 1
We obtain
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 148/197
14.3
U 1 ~ 8 ~ [ 2 ] + [ 1 2 ] ~ S 3 = [ 3 2 + [ 1 3 2 ,
U 1 ~ S 3 .~ . [ 2 ] + [ 1 2 ] ~ ' S = 2 1 2 , 1 2 •
N a k a y a m a ' s c o n j e c t u r e i m p l i e s t h a t [ 2 , 1 ] f o r m s i t s o w n 2 - b l o c k a n d
i s m o d u l a r i r r e d u c i b l e .
B e s i d e s t h i s b l o c k S p o s s e s s e s o n l y o n e f u r t h e r p r i n c i p a l i n d e -
c o m p o s a b l e , h e n c e t h i s o n e h a s t h e s a m e d e c o m p o s i t i o n a s [ 3 ]+ [ I 3 ]
a n d w e o b t a i n t h e d e c o m p o s i t i o n m a t r i x o f S f o r p = 2:
D ~ , 2 = [ 1 3 -]
t r 2 , 1 ] •
( P o r t h e s a k e o f s i m p l i c i t y w e o f t e n o m i t t h e O ' s . )
T h e n
[ 3 ] = 0 1 0 , [ 2 , 1 ] : 0 1 , [ 1 3 ] . 01 10 .
T h u s
' 7 . 1 4
~ 1 ~ s 4 ~ [3 2 + [ 1 3 ] $ s _- ~
1 1
U 1 I ' S4 ~ . [ 3 ] + [ 1 3 2 I S 4 = [ 4 2 + [ 3 , 1 2 + [ 2 , 1 2 2 + [ 1 4 2 ,
o oU 2 ~' S4 ~ [ 2 , 1 ] f 8 4 . = [ 3 , 1 ] + [2 2 ] + [ 2 , 1 2 ] ,
1 1U 2 t 8 4 ~ - [ 2 , 1 ] ~ 8 4 . = , ~ •
S h a s e x a c t l y t w o 2 - r e g u l a r c l a s s e s s o t h a t D 1 ,2 ~ c o n s i s t s o f
2 columns.
7 . 1 4 i m p l i e s , t h a t t h e c o l u m n s o f t h e m a t r i x
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 149/197
144
7 . 1 5 R 4 , 2 : =
1 [ 4 ]
1 1 [ 3 , 1 ]
o I [ 2 2 ]
1 I [ 2 , 1 2 ]
1 [ 1 4 . ]
a r e l i n e a r c o m b i n a t i o n s ( w i t h n o n n e g a t v e i n t e g r a l c o e f f i c i e n t s ) o f
t h e c o l u m n s o f D ; , 2 .
R 4 , 2 i s a m a t r i x o f t h e s a m e s h a p e a s D ~ , 2 a n d i t i s a l o w e r t r i -
a n g u l a r m a t r i x . H e n c e i t s f i r s t c o l ! ~ mn c o n t a i n s t h e f i r s t c o l ~ m n
o f D ~ a n d i ts s e c o n d c o l u m n c o n t a i n s t h e s e c o n d c o l l m ~ o f D 1,2 ¢,2"
T h e t r i a n g u l a r f o r m i m p l i e s f u r t h e r m o r e , t h a t t h e s e c o n d c o l u m n
o f R 4 , 2 c a n n o t c o n t a i n t h e f i r s t c o l u m # o f D I , 2 s o t h a t t h e s e -
c o n d o o l 1 ~ m~ o f R 4 , 2 i s e q u a l t o t h e s e c o n d c o l u m n o f D 1 , 2 ' s i n c e
d e c o m p o s i t i o n n u m b e r s a r e i n t e g e r s . T h i s s e c o n d c ol 1~ mn o f R 4 , 2
c a n n o t b e s u b t r a c t e d f r o m t h e f i r s t c o l u m n o f R 4 , 2 w i t h o u t g e t t i n g
n e g a t i v e e n t r i e s s u c h t h a t t h e f i r s t c o l u m n o f R 4 , 2 is e q u a l t o
t h e f i r s t c o l u m n o f D 14,2:
? . 1 , , ~ D 14 , 2 =
1 [ 4 ]
1 1 [ 3 , 1 ]
0 1 [ 2 2 ]
1 1 [ 2 , 1 2 ]
1 [ 1 4 ] •
T h e n
[ 4 ] : 0 1 0 1 , [ . 3 , 1 ] : 0 1 0 , [ 2 2 ] ; 0 1 , [ 2 , 1 2 ] : 0 1 , [ 1 4 ] : 01 1 0 1 1
0 01
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 150/197
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 151/197
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 152/197
147
H e n c e t h e c o l u m n t o t h e e x t r e m e r i g h t o f t h e c o n s i d e r e d s u m m a n d
o f R n , p ( c f . e x a m p l e 7 . 1 8 ) i s a n i n t e g r a l m u l t i p l e o f t h e c o r r e s -
p o n d i n g c ol 1~ m~ o f D 1 T h u s w e h a v e t o c h e c k w h e t h e r t h i s c o l u m nn , p "
c a n b e d i v i d e d b y a n a t u r a l n u m b e r t o y i e l d a n e w c o l u m n o v e r ~ .
~ . ~ ! ~ I f t h e c o l u m n t o t h e e x t r e m e r i g h t o f t h e c o n s i d e r e d s u m m a n d
o f R n l P c a n b e d i v i d e d b y a n a t u r a l n u m b e r , t h i s d i v i s i o n h a s• , • , _ , . , , • , . , .
t o b e c a r r i e d o u t t o y i e l d t h e c o r r e s p o n d i n g c o l u m n o f In, p"
P r o o f: W e k n o w t h a t t h e C a r t a n m a t r i x
1 t~l ~1C n , p : = ~ n , p ~ n , p
( t I t h e t r a n s p o s e d m a t r i x ) h a s a d e t e r m i n a n t w h o s e v a l u e i s aD n , p
p o w e r o f p .
P u r t h e r m o r e i f D p a r i s e s f r o m D n ,l b y a d d i n g a c o l u m n o f D n , p
t o a n o t h e r c o l u m n o f I i t i s e a s y t o s e e t h a tD n , p ,
d e t ( t 1 , D I , ) = d e t 1D n , p n , p " C n , p "
W i t h t h i s i n m i n d i t is n o t t o o d i f f i c u l t t o c he c k , t h a t
d e t ( t R n , p R n , p ) = r ~ . 2 I.rkde tOn, p , (I)
D n , pf r i E N i s t h e m u l t i p l i c i t y o f t h e i - t h c o l u m n o f I i n t h e
i - t h c o l ~ m n o f R n , p ( a f t e r t h e s u i t a b l e r e a r r a n g e m e n t o f t he
c o l u m n s o f 1 h a s b e e n c a r r i e d o u t ) .D n , p
1 h a s m a x i m a l p - r a n k ( s ee C u r t i s /i n a l l y w e r e c a l l t h a t D n , p
R e i n e r [1 ] , ( 8 3 . 5 ) ) .
H e n c e i f i t i s p o s s i b l e w e h a v e t o d i v i d e t h e c o n s i d e r e d c o l u m n
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 153/197
1 4 8
t o t h e e x t r e m e r i g h t b y p. T h a t w e h a v e t o d i v i d e t h e s e e n t r i e s
b y o t h e r c o m m o n f a c t o r s w e s e e f r o m ( I) , r e c a l l i n g t h a t d e t C ~ , p
i s a p o w e r o f p .
q . e . d .
T h u s w e o b t a i n o n e c o l ! 3 m n o f D 1 a n y w a y .n , p
P o r e x a m p l e t h e s e c o n d c o l u m n o f 7 . 1 8 h a s t o b e d i v i d e d b y 2 : I n
11 1
2 1
1 1
1
[ 5 ]
[ 3 , 2 ]E 3 , 1 2 ][ 2 2 , 1 ][ 1 5 ]
[ 4 , 1 ][ 2 , 1 3 ]
7 . 2 0 R ~ , 2 : =
a t l e a s t t h e s e c o n d a n d t h i r d c o l u m n s a g r e e w i t h t h e c o r r e s p o n d i n g
o o l u m ~ s o f D 1
5 , 2 "
I t r e m a i n s t o d e c i d e w h e t h e r t h e s e c o n d c o l1 ~ m~ h a s t o b e s u b ~ r a o -
t h e f i r s t o n e i n R ~ , 2 t o o b t a i n D ~ , 2 .e d f r o m
T h i s c a n be d e c i d e d u s i n g a r e s u l t o f ~ . H . P e e l o n t h e d e o o m p o -
s i t i o m n u m b e r s o f [ n - 2, 2 ] .
B e f o r e w e m e n t i o n P e e l ' s r e s u l t w e g i v e t h e o t h e r g e n e r a l r e s u l t
o n d e c o m p o s i t i o n n u m b e r s o f S ( F a r a h a t [ I ], cf . a l s o K e r b e r [ 1 ])
a n d w h i c h i s o f e q u a l i m p o r t a n c e :
7 ~ 2 1 I f p d o e s n o t d i v i d e n , t h e n [ n - 1 , 1 ] i s i r r e d u c i b l e .m ,
I f p d i v i d e s n an d n> 2 , t h e n t h e r e a r e e x a c t l y 2 i r r e d u c i b l e
c o n s t i t u e n t s o f [ n - 1, 1 ] , e a c h o f t h e m w i t h m u l t i p l i c i t y 1,
a n d o n e o f t h e m i s t h e i d e n t i t ~ r e p r e s e n t a t i o n .
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 154/197
149
P e e l ' s r e s u l t ( P e el [ 1 ] ) r e a d s a s f o l l o w s :
7 , 2 2 1) If p d o e s ~ o t d i v i d e n - 2 w e d i s t i n g u i s h t h e c a s e s p = 2 an d
p~2s
a ) I n c a s e t h a t p ~ 2 a n d
( i) p ~ n - l , t h e n [ n - 2 , 2 ] i s i r r e d u c i b l e . I f
( i i ) p ] n - l , t h e n [ n - 2 , 2 ] h a s e x a c t l y ~ w o d i f f e r e n t
i r r e d u c i b l e c o n s t i tu e n t s , e a c h w i t h m u l t i p l i c i t y I,
o n e o f t h e m i s t h e i d e n t i t y r e p r e s e n t a t i o n .
b) If p=2 and
( i) n = 2 a + 1 , 2 ~ a , [ n - 2 , 2 ] i s i r r e d u c i b l e . I f
( i i ) n = 2 a + 1 , 2 I a , t h e n [ n - 2 , 2 ] c o n t a i n s e x a c t l y ~ w o i t -
r e d u c i b l e c o n s t i t u e n t s , e a c h w i t h m u l t i p l i c i t y I,
o n e o f t h e m i s th e i d e n t i t y r e p r e s e n t a t i o n .
2 ) I f o n t h e o t h e r h a n d p d i v i d e s n - 2 , a n d
a ) p = 2 w e h a v e t o d i s t i n g u i s h t h e f o l l o w i n g t w o c a s es :
( i) I f n = 2 a , 2 I a a n d a > 2 ( [2 ] a n d ~ a r e i r r e d u c i b l e
a s w e h a v e s e e n a b ov e ) , t h e n [ n - 2 , 2 ] p o s s e s s e s
e x a c t l y tw o d i f f e r e n t i r r e d u c i b l e c o n s t i t u e n t s, e a c h
o n e w i t h m u l t i p l i c i t y I, o n e o f t h e m i s o f d i m e n s i o n
n-2.
( i i ) I f n = 2 a , 2 t a , t h e n [ n - 2 , 2 ] c o n t a i n s e x a c t l y t h r e e
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 155/197
1 5 0
d i f f e r e n t i r r e d u c i b l e c o n s t i t u e n t s , e a c h o n e w i t h
m u l t i p l i c i t y I, o n e of t h e m is t h e i d e n t i t y r e p r e s e n -
t a t i o n , a n o t h e r o n e i s o f d i m e n s i o n n - 2 .
b ) If p $ 2, E n - 2 , 2 ] p o s s e s s e s e x a c t l y 2 d i f f e r e n t i r r e d u -
c i b l e c o n s t i t u e n t s , e v e r y o n e w i t h m u l t i p l i c i t y 1 , o n e
o f t h e m is t h e i r r e d u c i b l e r e p r e s e n t a t i o n [ n - 1 , 1 ]
(of. 7.21).
P r o m 7 . 2 2 I) b ) ( ii ) w e o b t a i n w i t h 7 . 2 0 :
[ 5 1
[ 3 , 2 ]![ 3 , 1 2 ]
7.2 3 D 1 = I I5 , 2 1 [ 2 2 , 1 ]
1 [ 1 5 ]
[ 2 , 1 ~ ] .
T h e r - i n d u c i n g p r o c e s s , N a k a y a m a ' s c o n j e c t u r e a n d 7 . 2 1 / 7 . 2 2 y i e l d
D ~ , 2 =
11 1
1 1
2 1
1 0
1 0
2 1
1 1
1 1
1
[ 6 ]
[ 5 , 1 ]
[ 4 , 2 ][ 4 , 1 2 ]
[ 3 2 ]
[ 2 3 ]
[ 3 ~ 1 3 ][ 2 z , 1 2 ]
[ 2 , 1 4 ][ 1 6 ]
[ 3 , 2 , 1 ] .
T h e a p p l i c a t i o n o f t he r - i n d u c i n g p r o c e s z t o D 1 y i e l d s t h e6 , 2
f o l l o w i n g m a t r i x ( w e u s e d 7 . 1 9 a n d 7 . 2 2 ) :
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 156/197
1 5 1
7 . 2 5 R 7 , 2 : =
1
0 1
1 1
1 I
I 0
1 0
1 1
1 1
0 1
1
1
2 1
1 1
1 J
[ 7 ][ 5 , 2 ]
[ 5 , 1 2 ][ 4 , 2 , 1
[ 3 2 , 1 ]
[ 3 , 2 2 ]
[ , 2 , 1 2
[ 3 , 1
[ 2 2 , 1 3
[ 1 7 ]
[ 6 , 1 ]
[ 4 , 3 ][ 4 , 1 3 ][ 2 3 , 1 ][ 2 , 1 5 ]
T o c he c k , t h a t t h i s m a t r i x i s t h e d e c o m p o s i t i o n m a t r i x o f S w e
u s e a n i c e t r i c k : 7 . 2 4 i m p l i e s t h a t t h e d i f f e r e n c e o f t h e c h a r a c -
t e r s o f ~ a n d [ 6 ] i s t h e B r a u e r c h a r a c t e r o f F 3 , t h e t h i r d
2 - m o d u l a r i r r e d u c i b l e r e p r e s e n t a t i o n o f S 6 w h i c h b e l o n g s t o t he
t h i r d c o l u m n o f D ~ , 2 . ~ 1° r s h o r t :
H e n c e w e m a y i n d u c e t o g e t
7 . 2 6 ~ z ? s 7 ~ ( [ 3 - N ~ ] ) t s ~ ~ t 7 - [ 6 ] t s
[ 4 , ' 3 ] * [3-~,1] - [ 7 ] - [ 6 , 1 ] .
N o w w e l o o k a t t h i s d e c o m p o s i t i o n a n d 7 .2 5 .
T h e r i g h t h a n d s i d e o f 7 . 2 6 c o n t a i n s e a c h 2 - m o d u l a r i r r e d u c i b l e
r e p r e s e n t a t i o n o f S w i t h n o n n e g a t i v e m u l t i p l i c i t y . F r o m 7 . 2 5
w e k n o w , t h a t [ 7] a s w e l l a s [ 6, 1 ] a r e i r r e d u c i b l e r e p r e s e n t a -
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 157/197
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 158/197
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 159/197
-q
I~
~
~
o
P
I~
r~
i -~.
o
~1
o
~
o
o"
(D
o
P
~
r~
~
o
I~
r~
¢
,n
H
o
~
o
I
~
I1
i
o
e
~
o
o
H.
°
I¢
,~
o
o
,~-~
e
I~
e
o
C~ io
r ~o
~
~
~
~~
~
o
~
~
0
~
~
~0
~
~
~
~
~
~~
~~~
~
~
0
~
~
~
~
~~
~
~
~
~
0
0~
~~
~
0
~
~
~
~
~
~~
~
~
~
~
~
0~
~~~
~
~
~
~
~
~
~
~
0
~
0
~
0
0
~~
~
0
~
~
0
0
~
~
0
0
~
~
~
~
0
~
~
-~~
D
~
D~~
'~~
~~
~~
0~
I~~-~
'~
~
.1
I~~~
"~
I~~~
~
~
P~~
~
.1~
~
~
D
~
o o H Is o o o t~ ~~
Io I
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 160/197
1 5 5
7.33
w o u l d c o n t a i n t h e e i g t h c o l u m m o f D ~ , 2 . T h i s i m p l i e s , t h a t
7 . 3 4
1
1
0 1
1 1
1 11 0
0 1
1
a r e t h e t w o c o l u m n s t o t h e e x t r e m e r i g h t o f D 19,2"
H e n c e t h e r e r e m a i n s t o e xa m i n e t h e f o l l o w i n g t w o p o s s i b i l i t i e s f o r
t h e s i x t h c o l n m n a n d t h e c o r r e c t e d s e v e n t h a n d e i g t h c o l n m n :
1 1
0 2 11 3 1
3 1 0 1
7.35 3 3 1 13 3 1 1I 3 1 0
3 1 0
0 2 1
1 1 1
T h e c o m b i n a t i o n o f t h e s e t w o p o s s i b i l i t i e s f o r th e f i r s t c o l n m n
g i v e s , t h a t
7 . 3 6
c o n t a i n s t h e f i r s t c o l u m n o f t h e c o r r e s p o n d i n g b o x o f D ~ , 2 .
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 161/197
156
T h u s i t r e m a i n s t o d e c i d e w h e t h e r
7 -37
10 1
1 1
0 0 1
0 1 1
0 1 I
1 1 0
0 0 1
0 1
1
[8,1][ 6 , 3 ~[ 6 , 1 J ]
[ 4 , 3 , 2 ][4,3,1 2 ]
[ 4 , 2 2 , 1 ][4,1 5 ]
[ 3 2 , 2 , 1 ][ 2 3 , 1 3 ]
[ 2 , 1 7 ]c a n b e a s u b m a t r i x o f D I9,2 or not.
T o d e c i d e t h i s w e c o n s i d e r a g a i n a s p e c i a l i n d u c e d c h a r a c t e r :
7 . 3 8 F ~ t s 9 = ( [ ~ , 2 ] - 2 1 8 ' i ) ~ s 9
= [ 4 , 3 , 2 ] + [ 3 " ~ ' ~ + [ 3 2 , 2 , 1 " ] - 2 1 9 ] - 2 1 8 , 1 ] .
T h i s d e c o m p o s i t i o n i m p l i e s , t h a t [ 4 , 3 , 2 ] + [ 3 2 , 2 , 1 ] c o n t a i n s a t l e a s t
t w i c e t h e i r r e d u c i b l e c o n s t i t u e n t [ 8 , 1] s o t h a t 7 . 3 6 d e s c r i b e s
t h e f i r s t c o l u m n o f t h e c o n s i d e r e d s u b m a t r i x o f D ~ , 2 .
I t r e m a i n s t o i n v e s t i g a t e t h e s u b m a t r i x o f 7 . 3 2 w h i c h c o n t a i n s
t h e i d e n t i t y r e p r e s e n t a t i o n .
T h a t t h e o n l y p o s s i b i l i t y f o r t h e f o u r t h c o l u m n h a s t o b e d i v i d e d
b y 2 w e o b t a i n f r o m 7 . 1 9 s i n c e t h e f i f t h c ol l, mn c a n n o t b e s u b -
t r a c t e d . H e n c e 7 .3 1 s u g g e s t s t o e x a m i n e t h e m a t r i x 7 . 3 9 ( s e e t h e
f o l l o w i n g p a g e ) , w h o s e i - t h c o l u m n c o n t a i n s t h e i - t h c ol ~3 mn o f
D~, 2 (I~i~5).
O b v i o u s l y i t r e m a i n s t o c h e c k th e f i r s t a n d t h e s e c o n d c o l ~ m n o f
7 . 3 9 . T h e o t h e r c o l u m n s a r e c o l u m n s o f D I , 2 a s t h e y s t a n d s i n c e
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 162/197
157
f r o m t h e s e c o l u m n s n o t a n y o t h e r o n e o a n b e s u b t r a c t e d w i t h o u t
y i e l d i n g n e g a t i v e e n t ri e s .
7 . 3 9
1
1 1
2 1
1 1 1
0 1 0 1
2 1 1 1
2 0 1 0
3 2 1 1
2 2 0 1
2 1 0 1
3 2 1 1
2 0 0 0
2 0 1 0
2 1 0 1
2 1 1 1
1 1 1 0
2 1 0
0 1 1
1 1
1
[ 9 ][ 7 , 2 ][ 7 , 1 2 ]
[ 6 , 2 , 1 ]
[ 5 , 4 ][ 5 , 3 , 1 ][ 5 , 2 2 ]
[ 5 , 2 , 1 2 ]
[ 5 , 1 4 ][ 4 2 , 1 ]
[ 4 - , 2 , 1 3 ]
[ 3 3 ][ 3 2 , 1 3 ]
[ 3 , 2 3 ][ 3 , 2 2 , 1 2 ]
[ 3 , 2 , 1 4 ]
[ 3 , ~ ]
[ 2 4 , 1 ]
[ 2 2 , 1 5 ]
[1 9 ]
T o e x a m i n e t h e f i r s t a n d s e c o n d c o l u m n o f th i s m a t r i x w e c o n s i d e r
7 . 4 o ~ 4 t s 9 - - ( [ 8 ] + [ 5 , 3 ] - [ 6 , ~ 1 ) t s
: [9 ]+ [8 ,1 ]+ [6 ,3 ]+ [5 ,4 ]+ [5 ,3 ,1 ]-[7,1--~-[6,2,'I"]'-[6,1-~] •
S i n c e t h e f i r s t t h r e e r o w s o f 7 . 3 9 a r e c o r r e c t a s t h e y s t a n d ( c f .
7 . 2 2) , t he r e p r e s e n t a t i o n [ 7 , 1 ~ + [ 6 , 2 , 1 i c o n t a i n s t h e s e c o n d i r r e -
d u c i b l e r e p r e s e n t a t i o n [ 7 , 2] - [ 9 ] w i t h m u l t i p l i c i t y 2 ( n o t i c e t h a t
t h e t h i r d c o l n m n o f 7 . 3 9 c a n n o t b e s u b t r a c t e d f r o m t h e s e c o n d
o n e ) . H e nc e 7 . 4 0 i m p l i e s t h a t [ 5 , 4 ] + [ 5 , 3 , 1 ] c o n t a i n s [ 7 , 2 ] - [ 9 ]
a t l e a s t t w i c e s u c h t h a t n e i t h e r t h e f o u r t h n o r t h e f i f t h c o l u m n
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 163/197
158
has to be subtrac ted from the second col~mn of 7.39.
The secon~ col1~mn of 7.39 is therefore correct as it stands.
It remains to consider the first column and to decide whether the
third and/or fifth coll,mn have to be subtracted or not.
The first three entries of this col~Imn are cor rect as the y stand.
W e c o n s i d e r t h e d e c o m p o s i t i o n
7.41 ~3 ~ $9 ~ ([8]+[6, 2]-[7, 1]) ~ S 9
=
[8,1]+[7,2]+[7,1--~ contains thrice the irreduci ble repr esenta tion
[9], hence at least this is valid f or [9]+[7,2]+[6,2,1]. Th us the
third column has not to be subtracted from the first one so that
even the first four entries of this col1~mn agree wit h D I9,2"
W i t h t h i s w e r e t u r n t o 7 . 40 : [ 7 , 1 ~ + [ 6 , 2 , 1 ] c o n t a i n s th r i c e th e
irreducible constituen t [9] such that this represent atiau is con-
tained in [9]+[ 5,3,1] at least with multiplic ity 3. Hence also the
fifth column has not to be subtracted from the first one.
Hence 7.42 (on page 159) is the deco mpositi on matr ix of S 9 with
respect to p=2.
T h u s w e h a v e v e r i f i e d w i t h o u t a n y a n e x p l i c i t r e d u c t i o n o f a r e -
prese ntatio n the decomp ositio n number s of S for p=2 and n_(9
whi ch Robinson gave (Robinson [5],[6]). We have shown, how a com-
b i n a t i o n o f t he r - i n d u c i n g p r o c e s s t o g e t h e r w i t h a u s e o f F a r a h a t ' s
and Peel's results yields these far reaching results. But it
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 164/197
m
0
m
h
'
~.~
•
0
~
.
h
P
O
~
"
o
o
m
I~
~
o
°
o
0
~
~
.
0
c
~
0
-4
~+
0
P~
--
~.
0
4~
o
~
,a
0
N
I~
o
I
ro
0
0
0
0
(D
I
I~
c
0
m
~
+
(~
k
~.
~
O]
k
I
~
0
~
~
~
~
~
~
0
~
~
0
~
0
~
~
0
~
~
~
0
~
~
~
~
~
~
~
~
~
~
~
~
0
~
~
~
~
~
~
~
~
~
~
0
0
~
~
~
~
0
~
~
~
~
~
~
~
0
~
0
~
0
0
~
~
~
0
~
~
0
0
~
~
0
0
~
~
~
~
0
~
~
k
2
4
~
~
~,
--~
~
0
~
k/~L.._~ ~
--~
,,
~
k2~
--~
~
~
.
.a
~
--.%
,.~
--~
--~
f
O
L
-
~
~
4
-.~
~
k,W
~
~
C.
~
D
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 165/197
160
7 . 4 3
11 1111
2 111011211100111302111301001¢131112121100010104 . 1 1 0 1 1 15 1 3 1 2 1 15 1 2 1 1 1 12 1 2 1 1 0 0
21101012111101210000151211112111101
51312114 .1311102111 00021000012110101411011130100130211121100
00101001111011111111
( cf . t h e t a b l e 2 - 1 0 i n R o b i n s o n [ 5] , A p p e n d i x , w h i c h h a s t o b e
c o r r e c t e d ) . T h e l a s t f o r c o l u m n s o f 7 . 4 3 a g r e e w i t h t h e l a s t f o u r
c o l ~ m n s o f th e c o r r e s p o n d i n g s u b m a t r i x o f D !10,2"
T h e s e m e t h o d s h a v e b e e n u s e d a l s o f o r t h e c as e p = 3 , w h e r e t h e
f i r s t d i f f i c u l t y a r i s e s a t n= 8 . T h e q u e s t i o n i s w h e t h e r E 5 , 3 ]
c o n t a i n s [ 8] o r n o t . T h e a n s w e r i s n e g a t i v e : [ 5 , 3] d o e s n o t c o n -
t a i n [ 8] a n d u s i n g t h i s r e s u l t , t h e d e c o m p o s i t i o n m a t r i c e s h a v e
b e e n c a l c u l a t e d u p t o n = 1 0 ( K e r b e r / P e e l [ I] ). T h e r e a d e r c a n f i n d
o
t h e r e a n e c e s s a r y a n d s u f f i c i e n t c o n d i t i o n t h a t [ n - 3 , 3 ] c o n t a i n s
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 166/197
161
I nS . P o r f u r t h e r i n t e r e s t i n g r e s u l t s e s p e c i a l l y o n t h e d e c o m p o -
s i t i o n o f h o o k - r e p r e s e n t a t i o n s I n - r , 1 r ] t h e r e a d e r i s r e f e r r e d
t o P e e l [ 2 ] .
C o n c l u d i n g t h e s e c o n s i d e r a t i o n s o f t h e d e c o m p o s i t i o n n u m b e r s o f
S a n d g a t h e r i n g u p o u r e x p e r i e n c e s w e d a r e t o g i v e a c o n j e c t u r e :
7 . 4 4 C o n j e c t u r e : T h e s u b m a t r i c e s o f w h i c h t h e d e c o m p o s i t i o n m a t r i x
Dn,pl of S for p is a dire ct s um are for a
s u i t a b l e r e a r r a n g e m e n t o f t h e c o l 1~ m ns l o w e r
t r i a n g u l a r m a t r i c e s w i t h 1 's a l o n g t h e l e a d i n g
d i a g o n a l , i f t h e f i r s t r o w s o f th e c o n s i d e r e d
s u b m a t r i x c o r r e s p o n d t o d i a g r a m s w i t h n o p r o w s
o f e q u a l l e n g t h i n t h e i r n a t u r a l o r d e r .
P a r t s o f t h i s c o n j e c t u r e b u t n o t t h e f u l l s t a t e m e n t h a v e b e e n
prove d by Ro bin so n and 0.E. Taul bee (Robins on [5], Taulbee [I]).
C o n c l u d i n g t h i s s e c t i o n w e w o u l d l i k e t o i n v e s t i g a t e w h a t c a n b e
s a i d a b o u t t h e d e c o m p o s i t i o n m a t r i x D I o f A n if D 1 i s k n o w n .A n , P S n , P
7 . 6 y i el d s t h e d i s t r i b u t i o n o f t h e o r d i n a r y i r r e d u c i b l e r e p r e s e n -
tatio ns of A n into p-blo cks Henc e for to obtain D I it remain s• An, p
t o d e s c r i b e h o w w e c a n g e t i t s c o l u m n s f r o m t h e c o l u m n s o f D IS n , P
a n d t o d e s c r i b e w h a t h a p p e n s w i t h t h e c o r r e s p o n d i n g e n t r y o f
D IS n , P , i f t h e r e p r e s e n t a t i o n s a r e r e s t r i c t e d t o A n .
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 167/197
162
A s i n t h e o r d i n a r y c a s e w e c a n a p p l y C l i f f o r d ' s t h e o r y o f r e p r e -
s e n t a t i o n s o f g r o u p s w i t h n o r m a l d i v i s o r s . O u r a i m i s t o d e s c r i b e
m o d u l a r i r r e d uc i b l e r e p r e s e n t a t i o n s F o f S w h o s e r e s t r i c t i o n is
r e d u c i b l e r e s p. i r r e d u c i b l e .
F r o m C l i f f o r d ' s t h e o r y w e c o n c l u d e t h a t t h e ir r e d u c i bl e r e p r e s e n -
t a t i o n s o f S o v e r a n a l g e b r a i c a l l y c l o s e d f i e l d K ( o f a n y c h a -
r a c t e r i s t i c ) c a n b e o b t a i n e d i n t h e f o l l o w i n g w a y : T a k e a n i r r e -
d u c i b l e r e p r e s e n t a t i o n s F A of A a n d f i n d it s i n e r t i a g r o up . S i n c e
ISn:Anl!2 this inertia group is A or S . If A is the inerti a
g r o u p , t h e n P A f S n i s a n i r r e d u c i b l e r e p r e s e n t a t i o n o f S . I f S
i s t h e i n e r t i a g r o u p o f F A , t h e F c a n b e e x t e n d e d t o a n i r r e d u -
c i bl e r e p r e s e n t a t i o n ~ A o f S n, a n d w i t h t h i s r e p r e s e n t a t i e n w e
c a n c o n s t r u c t t w o i r r e d u c i b l e r e p r e s e n t a t i o n s o f S n:
FA = ~A @ [ ] ' @
(whi ch need n ot be dif fere nt, e.g. if char K = 2: i2] = [I--~, and
he nc e ~A = ~ A @ [1--1~).
A n d i n t h i s w a y w e o b t a i n a l l t h e i r r e d u c i b l e r e p r e s e n t a t i o n s o f
S •
T h i s i m p l i e s :
I f F i s a n i r r e d u c i b l e 2 - m o d u l a r r e p r e s e n t a t i o n o f S ( n >1 ) ,. , . , ,
t h e n t h e f o l l o w i n g i s v a l i d :
(i) F S & A red uci ble ~ Z FA: F S = F ~ S n.
(ii)Fs ~ P8 @ [ln] ~ PS $ ~ = (P8 [ln] ) $ An irredu cible.
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 168/197
163
I f a= ~ ' , t h e n [ ~ ] ~ An s p l i t s i n t o t w o m u t u a l l y c o n j u g a t e a n d i r -
r e d u c i b l e r e p r e s e n t a t i o n s o f A n :
[a] ~ A = [u]+ + [u]-
s o t h a t
T h u s a l s o
[~]+(a) ~ [~ ]- , V a E 8 n \ A n .
y ( a ) ~ i 1 i
a n d h e n c e t h e c o n s t i t u e n t s o f [ ~ ] - a r e c o n j u g a t e s o f t h e c o n s t i -
tuents of [~]+.
T h i s i m p l i e s
• If PS ~ PS @ [1'hi' and t he mu lt ip li ci ty of PS in [~] is odd
a n d ~ = ~ ' t h e n P s ~ A n i s r e d u c i b l e •
S u p p o s e n o w t h a t u s i n g 7 . 4 6 w e h a v e s u c c e e d e d i n p i c k i n g o u t t h e
c o l u m n s of D I w h i c h b e l o n g to m o d u l a r i r r e d u c i b l e r e p r e s e n -8 n , P
t a t i o n s P S w h o s e r e s t r i c t i o n t o A i s r e d u c i b l e ( i. e. P S is s e l f -
a s s o c i a t e d w i t h r e s p e c t t o A n ) . T h e n u n d e r c e r t a i n c i r c u m s t a n c e s
( w h i c h a r e f u l f i l l e d i n a l l t h e k n o w n c a s e s D ~ n , p ) w e a r e a b l e t o
eval uate D I at once.A n , P
L e t u s c o n s i d e r t h e r o w o f D I w h i c h b e l o n g s t o [ u] a n d t h eS n , P
c o l u m n w h i c h b e l o n g s t o P S " W e d e n o t e b y a r e s p . b t h e m u l t i p l i -
city of ~S resp. PS @ [ln] in i~] such that D I conta ins theS n , P
f o l l o w i n g s u b m a t r i x :
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 169/197
1 6 4
[ G ] . . .
[ ~ t ] ° . .
~ S
a
b
P s ® [ 1'n]
(i) If ~ + ~', PS ~ FS ® [In] :
I n t h i s c a s e t h e r o w o f [ 5 '] a n d t h e c o l u m n o f P S @ [ I n i h a s t o
b e c a n c e l l e d , a n d i n t h e r o w o f [ 5] ~ A w e h a v e i n t h e c o l u m n
o f P S ~ A n t h e d e o o m p o s i t i o n n u m b e r a + b, s i n c e
[~i " a~ S + b(F S @ [In]) +--.
[ 5 ] ~ A n . a ( ~ ~ A n ) + b ( F S @ [ I n ] ~ An) +...
= s A n + . . .
( i i) a + m' , P S " F S " [ I n] ' F S & A n i r r e d u c i b l e :
I t i s t r i v i a l , t h a t a i s t h e m u l t i p l i c i t y o f F ~ A i n [5 ] ~ A .
( i i i ) ~ + 5 ' , P S ~ A n r e d u c i b l e ( ~ P S N ~ S @ [ l n ] ) :
T h e n F S ~ A n ~ F S + F S w i t h t w o m u t u a l l y c o n j u g a t e a n d i r r e d u c i b l e
r e p r e s e n t a t i o n s ~ o f A . O b v i o u s l y [ ~] I A c o n t a i n s F ~ a s w e l l
a s F ~ w i t h m u l t i p l i c i t y a .
( i v ) a -- 5 ' , F s ~ F S ® [ I n ] :
a = b i s t h e m u l t i p l i c i t y o f P S ~ A n i n [ 5 ] a s w e l l a s i n [ ~ ] -
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 170/197
165
s i n c e F $ A i s s e l f c o m j u g a t e .
( v ) ~ = ~ ', P S N P S ® [ 1 hi , F S ~ A n i r r e d u c i b l e :
P S ~ A n i s s e l f c o n j u g a t e a g a i n . T h u s a = b i s e v e n a n d a / 2 i s t h e
m u l t i p l i c i t y o f P S ~ A n i n [ m ] + as w e l l a s i n [ ~ ]- .
T h e t h e o r y p r o v i d e s a n a n s w e r o n l y i f a = O o r a = I . I n t h i s
c a s e w e h a v e t h e s u b m a t r i c e s
o or °IC o ~ ] - o [ , , I - I
( r e s p. IO ~ ] i f w e u s e a n o t h e r d e n u m e r a t i o n ) .
G a t h e r i n g u p w e h a v e o b t a i n e d ( s ee P u t t a s w a m a i a h [1] , P u t t a s w a -
m a i a h / 2 o b i n s o n [1] , K e r b e r [3] ) :
I f D I c o n t a i n s t h e s u b m a t r i xS n , P
F S F s ~ [ 1 ~ ]
[ e , ] b a ,
t h e n i f
( i ) ~ ~ ~ ' P S ~ F S @ [ I n] ' D 1 c o n t a i n s t h e s u b m a t r i x, A n , P
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 171/197
166
~sSAn
[ = ] ~ , A n [ a + b ]
( i i ) I f ~ + = ', P S N F s @ [ s ni , P S ~ A n i r r e d u c i b l e :
F s ~ A n
[ ~ ] ~ A n [ ]
+ P S :i i i ) ~ ~ ~ , , P s ~ A n " P s +
[ ~ s ~ A n [ a a ]
(iv) ~ = ~', PS + PS @ '['ln']':
[ = ] +
[ a ] -
P S ~ A n
[:1( v) a = ~ ', P S N p S @ [ I n ] ' P S ~ A n i r r e d u c i b l e :
F ~ A
E ~ ÷ r ~ / 2 ]
[ - ] +
resp.
o]I .
A s a n e x a m p l e w e g i v e t h e d e c o m p o s i t i o n m a t r i x o f A w h i c h a r i s e s
f r o m t h e d e c o m p o s i t i o n m a t r i x o f S f o r p = 3 g i v e n i n K e r b e r /
P e e l [ 1 ] ,
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 172/197
(~
N
m
N
o
et-
N
N
~
~u
~
C
~
F
N
•
N
N
~
~
•
•
~,
~'
e
O O
° c
U
-
O
O
-~-A O
O ro
-~O
.~O
O .~
O
O ro
-~ O
O -~ O
O -A -~ -~ -A
.A ro
O
O
O
O
O
.L~
O -A
O
O .A -A O
O .A .~
O
~
,A
O
O ro
-A -~~
I~O O
"A
.L
o
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 173/197
1 6 8
8 . G e n e r a l i z e d d e c o m p o s i t i o n n u m b e r s o f
s y m m e t r i c a n d a l t e r n a t i n g g r o u p sl|
I f p i s a p r i m e n u m b e r a n d G a f i n i t e g r o u p w i t h o r d i n a r y i r r e d u -
c i b l e c h a r a c t e r s C , B r a u e r c h a r a c t e r s k o f t h e i r r e d u c i b l e
Ip - m o d u l a r r e p r e se n t a t io n s , a n d d e c o m p o s i t i o n m u m b e r s d i k w i t h r e -
s p e c t t o p w e h a v e f o r a p - r e g u l a r e l e m e n t g E G :
8 .1 ~ i (g ) = Z d ~ k ( g ) •
k
T h i s c a n b e g e n e r a l i z e d t o g e n e r a l g r o u p e l e m e n t s g .
A s i s w e l l k n o w n a n e l e m e n t g E G i s a p r o d u c t o f a u n i q u e l y d e t e r -
m i n e d p - e l e m e n t x w i t h a u n i q u e l y d e t e r m i n e d p - r e g u l a r y w h i c h
c o m m u t e s w i t h x :
8 . 2 g = x y = y x .
L e t u s c a l l x t he p - c o m p o n e n t , y t h e p - r e g u l a r c o m p o n e n t o f g .
g r u m s t h r o u g h a c o m p l e t e s y s t e m o f r e p r e s e n t a t i v e s o f t h e c o n j u -
g a c y c l a s s e s o f G if i n 8 . 2 x r u n s t h r o u g h a c o m p l e t e s y s t e m o f
t h e p - c l a s s e s o f G a n d y - w h i l e x i s f i x e d - r u n s t h r o u g h a c o m -
p l e t e s y s t e m o f r e p r e s e n t a t i v e s o f t h e p - r e g u l a r c l a s s e s o f t h e
c e n t r a l i z e r C G ( X ) o f x i n G . S i n c e C G ( 1 ) = G , t h e f o l l o w i n g r e s u l t
o f B r a u e r g e n e r a l i z e s 8 . 1:
I f x E G i s a p - e l e m e n t o f o r d e r p r a n d i f ~ k a r e t h e B r a u e r
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 174/197
169
c h a r a c t e r s o f 0 G (x ) w i t h r e s p e c t t o p , t h e n t h e r e e x i s t a l g e -
b r a i c i n t e g e r s d ~ k i n Q ( ~ ) ( ¢ a p r i m i t i v e p r - t h r o o t o f u n i t y )
d e p e n d i n g o n l y o n x an d s a t i s f y i n g
y E C G ( X ) , y p - r e g u l a r .
c i C xy ) = Z d ~ k ~ C y ) ,
k
(of. Ou rt is /R ei ne r [I ], $ 90A)
I f n o w D x i n d i c a t e s t h e m a t r i x o f t h e s e a l g e b r a i c i n t e g e r s
8 . 4 D x = = ,
i t c a n b e s h o w n, t h a t f o r a n x' c o n j u g a t e t o x t h e m a t r i x D x '
a r i s e s f r o m D x b y a p e r m u t a t i o n o f t he c o l u m n s . T h u s f o r a n i n -
xv e s t i g a t i o n o f t h e s e a l g e b r a i c i n t e g e r s d i k W e n e e d o n l y c o n s i d e r
t h e m a t r i c e s D x j f o r a c o m p l e t e s y s t e m , s a y f o r [ X l : = 1 , . . . , X u ] ,
o f r e p r e s e n t a t i v e s o f t h e p - c l a s s e s o f G .
F o r s u c h a f i x e d s y s t e m o f r e p r e s e n t a t i v e s w e d e n o t e f o r s h o r t
X8 . 5 D v = = l v < _u .
T h e m a t r i x
8 . 6 D : = ( D I , . . . , D u ) ,
w h i c h i s t h e r e f o r e u n i q u e l y d e t e r m i n e d u p t o a c o l u m n p e r m u t a t i o n
i s c a l l ed t h e g e n e r a l i z e d d e c o m p o s i t i o n m a t r i x o f G w i t h r e s p e c t
t o p. I t s e n t r i e s a r e c a l l e d t h e R e n e r a l i z e d d e c o m p o s i t i o n n u m b e r s
o f G w i t h r e s p e c t t o p .
I t s f i r s t c o l~ 3 m ~s c o n t a i n D I t h e d e c o m p o s i t i o n m a t r i x o f G .
I f y j a r e t h e r e p r e s e n t a t i v e s o f th e p - r e g u l a r c l a s s e s o f C G ( X v)
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 175/197
170
we indicate as follows:
8 . ?c i ~ v ( ~ iv . = ( ( x v y Q ) , : = ( y Q )
a n d h e n c e t h e m a t r i c e s
U
8.8 # := $ jv , Z := (Z 1,.. .,z )
v=l
satisfy the equation
8 . 9 Z = D # .
We would like to evaluate these matrices D of generalized dec om-
posit ion numbers of the symmetric group.
A t f i r s t w e n o t i c e t h a t s i n c e a m a t r i x o f B r a u e r c h a r a c t e r s i s
not singular:
8 . 1 0 D v = z V ( J V ) - 1 .
Z v is known fr om the charac ter table, thus it remains to derive
the matrices @v of the Braue r charact ers of centralizers of p-ele-
ments of S .
E S is a p-elem ent if and only if the lengths of all the cyclic
factors of ~ are powers of p, this is implied by 1.11.
Pro m 2.32 we obtain, that the centralizer of such a p-element is
a direct product of symmetries of cyclic p-groups:
8.11 If ~ E S is a p-el emen t of type T~ = (al,...,an) , then we
have for the centralizer of ~:
( ~ ) = × ( c i ~ S a ) .CSn i p pi
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 176/197
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 177/197
1 7 2
T h e c e n t r a l i z e r s o f t h e s e e l e m e n t s a r e o f t h e f o r m
0 ( ~ 1 ) = S 6 , 0 ( ~ 2 ) = 0 2 x 8 4 , C ( ~ 3 ) = O 2 ~ S 2 x S 2 .
0 ( ~ 4 ) = 0 2 % S 3 , 0 ( ~ 5 ) = 0 4 x S 2 , C ( ~ 6 ) = 0 4 x 0 2 .
( , , ) H e n c e w e n e e d o n l y t h e m a t r i c e s o f B r a u e r c h a r a c t e r s o f S i,
$ 2 , S a n d S . T h e s e m a t r i c e s a r e
[: 1]@ 1 = @ 2 = ( 1 ) a n d ' 3 = ' 4 = '
- 1
a s c a n b e e v a l u a t e d e a s i l y w i t h t h e k n o w n c h a r a c t e r t a b l e s
a n d t h e d e c o m p o s i t i o n m a t r i c e s D I D I a n d D I ( s e e2 , 2 ' 3 , 2 4 , 2
s e c t i o n 7 ) . T h u s w e o b t a i n
= = [1 2 i ] , 3 , 2 x , 2 ( 1 ) ,2 ' 4 X t I - , = =
' 4 = ' 3 = [1 2 - : ] ' ' 5 = ' 1 X ' 2 = ( 1 ) = ' 6
( ,1 h a s b e e n o m i t t e d s i n c e D ~ , 2 h a s b e e n e v a l u a t e d i n s e c t i o n
7 ) .
B e c a u s e
[ : 1 ] _ 1 _ _ i i / 3 , j 3 1- ~ [ 2 / 3 - ~ / 3 . I
a n dr 1 1 1 1
3 0 1 13 0 3 o
- ~ - 2 I
z ~ _ i _ ~ ~ z , _ ~ o= 0 0
3 0
2 -1
- 1 - 1
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 178/197
1 73
a s c a n b e r e a d o f f f r o m t h e c h a r a c t e r t a b l e o f $ 6, w e g e t
f o r t h e g e n e r a l i z e d d e c o m p o s i t i o n m a t r i x o f S 6 w i t h r e s p e c t
to p = 2:
D 6 , 2 =
1
1 11 1 1
2 1 1
1 0 1
1 0 1
2 1 1
1 1 1
1 1
1
I
I 1
I I
0 1
I 0
-I 0
0 - 1
-1 -I
-I -1
-I
1 -1 1
- 1 2 0 - t- 1 - 1
0 1
t - 1 - 1
1 1
1 - 1
t
,1 1
,o o
- 1
- 10
, 1 i - 1
,1 1
( t h e c o l u m n s b e l o n g i n g t o @ 3 = 1 5 = ~ 6 = ( 1 ) a g r e e w i t h t h e c o n -
c e r n i n g c o l u m n s o f t h e c h a r a c t e r t a b l e ) .
T h e g e n e r a l i z e d d e c o m p o s i t i o n n u m b e r s o f A n c a n b e e v a l u a t e d s i m i -
l a r l y a s l o n g a s t h e a p p r o p r i a t e c e n t r a l i z e r s o f p - e l e m e n t s a r e
d i r e c t p r o d u c t s o f g e n e r a l i z e d a l t e r n a t i n g g r o u p s C i % A a . o r
P p ~
h a v e (I ) a s m a t r i x o f B r a u e r c h a r a c t e r s ( s u c h t h a t t h e c o l u m n s
a g r e e s w i t h a c o l u m n o f t h e c h a r a c t e r t a b l e ). I n t h i s w a y t h e
g e n e r a l i z e d d e c o m p o s i t i o n m a t r i c e s o f A n w i t h r e s p e c t t o p= 3 h a v e
b e e n c a l c u l a t e d f o r n ~ 7 ( K e r b e r [ 1] ).
D u r i n g t h e s e c a l c u l a t i o n s w e se e t h a t ~ o t h e r w i s e t h a n i n t h e c a s e
o f t h e s y m m e t r i c g r o u p ~ t h e g e n e r a l i z e d d e c o m p o s i t i o n n u m b e r s o f
A n a r e n o t i n g e n e r a l r a t i o n a l i n t e g e r s , e . g.
8 . 1 6
, 3 3 " -
I
( - 1 - i W ) / 2
i s t h e g e n e r a l i z e d d e c o m p o s i t i o n m a t r i x o f A 3 f o r p = 3. T h u s
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 179/197
174
(K er be r [I S) :
8 . 1 7 T h e g e n e r a l i z e d d e c o m p o s i t i o n m u m b e r s o f a l t e r n a t i n g g r o u ps
a r e n o t i n g e n e r a l r a t i o n a l i n t e g r a l .
N e v e r t h e l e s s ( O s i m a [ 5 ]) :
8 . 1 8 T h e g e n e r a l i z e d d e c o m p o s i t i o n n u m b e r s o f a l t e r n a t i n g g r o u p s
a r e r a t i o n a l i n t e g r a l f o r p = 2 .
P r o o f : T h e d e c o m p o s i t i o n n u m b e r s o f A n a r e r a t i o n a l i n t e g r a l b y
d e f i n i t i o n , t h u s D I is a m a t r i x o v e r 2 .
H e n c e i t s u f f i c e s t o s h o w t h a t @ v a n d t h e Z v ar e m a t r i c e s o v e r Z
i f v > 1 .
T h u s i t is e n o u g h t o p r o v e t h a t t he B r a u e r c h a r a c t e r s w i t h r e s p e c t
t o p = 2 o f c e n t r a l i z e r s o f 2 - e l e m e n t s ~ I o f A n a r e r a t i o n a l i n t e -
g r a l a n d t h a t t h i s i s v a l i d a l s o f o r t h e v a l u e s o f t h e o r d i n a r y
i r r e d u c i b l e c h a r a c t e r s o f 2 - s i n g u l a r e l e m e n t s o f A n -
T h e l a s t s t a t e m e n t i s v a l i d a s c an b e s e e n f r o m P r c b e n i u s '
t h e o r e m 4 .5 5 , s i n c e p e r m u t a t i o n s o f s p l i t t i n g c l a s s e s a r e o b v i o u s -
l y 2 - r e g u l a r . I t r e m a i n s t o p r o v e , t h a t t h e v a l u e s o f t h e B r a u e r
c h a r a c t e r s w i t h r e s p e c t t o p = 2 o f c e n t r a l i z e r s o f 2 - e l e m e n t s i n
A n a r e r a t i o n a l i n t e g r a l .
T h u s t h e p r o o f o f t h e f o l l o w i n g l e m m a ( O s i m a [ 5 ]) c o m p l e t e s t h e
p r o o f o f 8 . 1 8 :
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 180/197
175
8 . 1 9 I f ~ $I i s a 2 - e l e m e n t o f A n , t h e n t h e i r r e d u c i b l e B r a u e r
c h a r a c t e r s o f ( ~) w i t h r e s p e c t t o p = 2 r e m a i n i r r e d u c i b l eC S n _ _ _
i f t h e y a r e r e s t r i c t e d t o C A n ( ~ ) s u c h t h a t t h e v a l u e s o f t h e
B r a u e r c h a r a c t e r s o f C A n ( ~ ) a r e r a t i o n a l i n t e g r a l a s w e l l
( o f . 8 o 1 3 ) .
P r o o f : W e s h a l l s h o w t h a t t h e r e i s a s u b g r o u p o f C A n ( ~ ) w h i c h h a s
t h e s am e m a t r i x o f B r a u e r c h a r a c t e r s a s C S n ( ~ ) .
L e t ~ b e a n e v e n 2 - e l e m e n t o f S s u c h t h a t ~ I a n d h e n c e
CS n( ~) = ×i (C i% Sa i) = ×j (C2 J~%S 2 j) = ×j (C*~S~2 2 ) .
~ 1 i m p l i e s t h a t t h e r e i s a k > 1 s o t h a t a k > 0 . L e t u s f i x s u c h-- 2
a k . A s u b g r o u p o f C S n ( ~ ) w i t h t h e s a m e m a t r i x o f B r a u e r c h a r a c -
t e r s a s C S n ( ~ ) i s
G : = S ' S ' × ( C 2 k ~ S a 2 k ) × S 'l X . . . X X . . . .a 2 k - 1 a 2 k + 1
L e t u s c o n s i d e r t h e s u b g r o u p
G + := G G A ~ CA n(~ ) •
W e w o u l d l i k e t o s h o w , t h a t G + h a s t h e s a m e i r r e d u c i b l e B r a u e r
c h a r a c t e r s a s G a n d h e n c e a s C S n ( ~ ) , w h a t i m p l i e s t h a t t h e s t a t e -
m e n t 8 . 1 9 i s v a l i d .
~ r o m C l i f f o r d ' s t h e o r y o f r e p r e s e n t a t i o n s o f g r o u p s w i t h n o r m a l
d i v i s o r s w e k n o w , t h a t a n o r m a l d i v i s o r N o f i n d e x 2 i n B h a s
t h e s am e i r r e d u c i b l e B r a u e r c h a r a c t e r s a s B i f n o 2 - r e g u l a r c o n j u -
g a c y c l a s s o f B s p l i t s i n t o c o n j u g a c y c l a s s e s o f N .
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 181/197
1 7 6
H e n c e i t s u f f i c e s t o s h o w t h a t n o 2 - r e g u l a r c l a s s o f G s p l i t s i n t o
t w o 2 - r e g u l a r c l a s s e s o f G + .
I f C i s a 2 - r e g u l a r c l a s s o f G i t i s a p r o d u c t
0 = C 1 0 2 0 4 . . .
' if j~k, andf 2 - r e g u l a r c l a s s e s C j o f t h e d i r e c t f a c t o r s S a 2 j
C i s a 2 - r e g u l a r c l a s s o f 0 k ~ S a .
2 2
' s u c h t h a tr o m t h e r e s u l t s o f s e c t i o n 3 w e o b t a i n t h a t C E S k '
2a l l t h e f a c t o r s C i a r e c o n t a i n e d i n G + a s w e l l .
I t is o b v i o u s , t h a t t h e f a c t o r s C i d o n ' t s p l i t i n t o G + - c l a s s e s i f
i > I . H e n c e i t r e m a i n s t o s h o w t h a t C I d o e s n o t s p l i t , w h i c h c a n b e
p r o v e d a s f o l l o w s .
S e t p b e a n y o d d p e r m u t a t i o n o u t o f S 'l ; s i n c e k > O t h e r e i s a n
o d d p e r m u t a t i o n ~ E C k ~ S a a n d w e h a v e p a E G + . H e n c e C I d o e s
2 2
n o t s p l i t .
T h i s c o m p l e t e s t h e p r o o f o f 8 . 1 9 a n d s o a l s o o f 8 . 1 8.
q . e . d .
H e n c e ( O s i m a [ 5 ] ) :
8 . 2 0 I f ~ 1 i s a 2 - e l e m e n t o f t y p e T ~ = ( a l , . . . , a n ) o f A n ,
t h e n ( ~) a s w e l l a s ( ~) h a v eCSn CAn
~ a l x ~ a 2 x ~ a ¢ x . - .
a s m a t r i x o f B r a u e r c h a r a c t e r s w i t h r e s p e c t t o p = 2 i f ~ a
2 j
i s t h e m a t r i x o f t h e 2 - m o d u l a r B r a u e r c h a r a c t e r s o f S .
2 ~
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 182/197
177
U s i n g t h i s l e m m a M . 0 s i m a e v a l u a t ed t h e ge n e r a l i z e d d e c o m p o s i t i o n
m a t r i c e s o f A w i t h r e s p e c t to p = 2 f o r n = 6 , 7 , 8 , 9 ( O s i m a [ 5] ) , t h e
m a t r i c e s f o r n ~ 7 h a d a l r e a d y b e e n k n o w n ( K e r b e r [ I ]) .
T h i s s h o w s , t h a t f o r t o p r o v e t h a t t h e g e n e r a l i z e d d e c o m p o s i t i o n
n u m b e r s o f a f i n i t e g r o u p G w i t h r e s p e c t t o p a r e r a t i o n a l i n t e -
g e r s i t s u f f i c e s t o s h o w t h a t t h e v a l u e s o f t h e B r a u e r c h a r a c t e r s
o f c e n t r a l i z e r s o f p - e l e m e n t s a s w e l l a s t h e v a l u e s o f o r d i n a r y
i r r e d u c i b l e c h a r a c t e r s o n p - s i n g u l a r e l e m e n t s a r e r a t i o n a l i n t e -
g r a l . W e w o u l d l i k e t o c h e c k w h e t h e r t h i s i s t r u e f o r c e r t a i n
w r e a t h p r o d u c t s G ~ S .
8 . 2 1 I f G F ( p ) i s a s p l i t t i n g f i e l d f o r t h e c e n t r a l i z e r s o f t h e
p - e l e m e n t s ~ I o f t he f i n i t e g r o u p G a n d i f t h e v a l u e s o f t h e
o r d i n a r y i r r e d u c i b l e c h a r a c t e r s w i t h r e s p e c t t o p o f G ~ S o n
p - s i n g u l a r e l e m e n t s a r e r a t i o n a l i n t e g r a l, t h e n t h e g e n e r a -
l i z e d d e c o m p o s i t i o n n u m b e r s o f G % S n w i t h r e s p e c t t o p a r e
r a t i o n a l i n t e g r a l .
P r o o f : S e t ( f; ~ ) b e a p - e l e m e n t o f G ~ S a n d o f t y p e ( a i k ). F o r i t s
c e n t r a l i z e r w e h a v e ( cf . 3 . 2 5 ) :
8 . 2 2 ~ x )- i , k k ik
H e n c e i t s u f f i c e s t o c o n s i d e r t h e B r a u e r c h a r a c t e r s o f t h e f a c t o r s
8 . 2 3 O G ~ S k ( f ~ k ; ~ k ) - S a i k •
W e w o u l d l i k e t o s h o w t h a t t h e v a l u e s o f t h e i r B r a u e r c h a r a c t e r s
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 183/197
1 7 8
w i t h r e s p e c t t o p a r e r a t i o n a l i n t e g r a l .
F r o m t h e r e s u l t s o f s e c t i o n 5 w e o b t a i n t h a t i t s u f f i c e s t o s h o w
t h a t t h e p - m o d u l a r r e p r e s e n t a t i o n s o f
i . j8 . 2 4 C G , , ~ k ( f i k , ~ i k )c a n b e w r i t t e n o v e r G P ( p ) . B u t t h i s i s v a l i d s i n c e 8 . 2 4 i s a n e x -
t e n s i o n o f th e c e n t r a l i z e r o f a p - e l e m e n t o f G w i t h a c y c l i c
p - g r o u p ( c f. 3 . 1 9 ).
T h u s G F ( p ) i s a s p l i t t i n g f i e l d f o r t h e s u b g r o u p s 8 . 2 4 a n d h e n c e
f o r t h e b a s i s g r o u p o f 8 . 2 3 a s w e l l . T h i s i m p l i e s ( s e e s e c t i o n 5 )
t h a t G F ( p ) i s a s p l i t t i n g f i e l d f o r t h e g r o u p s 8 . 2 3 , t o o , s i n c e i t
i s a s p l i t t i n g f i e l d f o r s y m m e t r i c g r o u p s S a i a s w e l l .
H e n c e G P ( p ) i s a s p l i t t i n g f i e l d f o r O G ~ S n ( f ; ~ ) ( s e e 8 . 2 2 ) s u c h
t h a t t h e v a l u e s o f i t s B r a u e r c h a r a c t e r s a r e r a t i o n a l i n t e g r a l .
T h e d e c o m p o s i t i o n n u m b e r s o f G % S n a r e r a t i o n a l i n t e g r a l b y d e f i n i -
t i o n , t h e v a l u e s o f t h e o r d i n a r y i r r e d u c i b l e c h a r a c t e r s o f G % S n
o n p - s i n g u l a r e l e m e n t s a r e r a t i o n a l i n t e g r a l b y a s s u m p t i o n , h e n c e
( o f. 8 . 1 0 ) t h e D v a r e m a t r i c e s o v e r Z .
q . e . d .
8 . 1 1 a n d t h e r e s u l t s o f s e c t i o n 5 i m p l y t h a t G F ( p ) i s a s p l i t t i n g
f i e l d f o r t h e c e n t r a l i z e r s o f p - e l e m e n t s i n S n, t h u s a s a s p e c i a l
c a s e o f 8 . 21 w e o b t a i n :
8.25 T h e g e n e r a l i z e d d e c o m p o s i t i o n n u m b e r s of S m ~ S w i t h r e s p e c t
t o p a r e r a t i o n a l i n t e g r a l f o r a l l m, n a n d p .
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 184/197
1 7 9
A s w e h a v e s e e n, t h e p - m o d u l a r i r r e d u c i b l e r e p r e s e n t a t i o n s o f t h e
c e n t r a l i z e r s C S n ( ~ ) o f p - e l e m e n t s ~ + I s u c h t h a t ~ E A r e m a i n i r -
r e d u c i b l e i f t h e y a r e r e s t r i c t e d t o CA n ( ~ ) s u c h t h a t G P ( p ) i s a
s p l i t t i n g f i e l d f o r C A n ( ~ ) a s w e l l . H e n c e a l s o 8 . 1 8 i s a s p e c i a l
c a s e o f 8 . 21 ( G : = A m , n = 1 ) . F o r G : = [I ] w e o b v i o u s l y o b t a i n 8 . 1 4 .
M u l t i p l y i n g D S n , P r e sp . D A n , P w i t h t h e t r a n s p o s e d o f it s c o m p l e x -
c o n j u g a t e w e g e t t h e m a t r i c e s
S+~ n,p.D Sn,P ~1 ~uSn ,p := = C ~ ... ~ C ,
8 . 2 6
C A n , P : = A t ~ n , p ' D A n , P = C p l ~ , .. ~ C p v ,
t h e ~ e n e r a l i z e d 0 a r t a n m a t r i x o f S r e s p . A n , c o n s i s t i n g o f
~i Pjs u b m a t r i c e s 0 r e sp . C a l o n g t h e l e a d i n g d i a g o n a l w h i c h a r e
t h e C a r t a n m a t r i c e s o f t h e c e n t r a l i z e r s o f t h e p - e l e m e n t s ~ i r e s p .
p j ( c f . C u r t i s / R e i n e r [ I ], ~ 9 0 A ) . F o r e x a m p l e
% 6 , 2 = 6 ,i] , , 16] , , 8] , [8].
4
T h e o r d i n a r y i r r e d u c i b l e c h a r a c t e r s o f t h e c e n t r a l i z e r
n(~) = X (C i~ Sa )
C S n i = 0 p p i
o f a p - e l e m e n t ~ o f S o f t y p e T ~ = ( a l , . . . , a n ) a r e o f c o u r s e t h e
p r o d u c t s
C = C ° C 1 - - . C n
o f i r r e d u c i b l e o r d i n a r y c h a r a c t e r s ~ i of t h e d i r e c t f a c t o r s
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 185/197
180
(C i := I, if ap i= 0 ).
S i n c e
0 i ~ S ap p i
n
0 S n ( ~ ) / O 1 ~ S a l = x (C i ~ S a )i=I p pi
p o s s e s s e s o n l y o n e p - b l o c k ( c f . 5 . 3 1) w e h a v e ( 0 s i m a [ 4 ]) :
8 , 2 7 T w o o r d i n a r y i r r e d u c i b l e c h a r a c t e r s C = C ° . . . C n a n d
C ' = C ° ' . . . C n ' o f O Sn (~ ). ( ~ a p - e l e m e n t o f t y p e T ~ = ( a l , . . . , a n ) )
b e l o n g t o t h e s a m e p - b l o c k i f a n d o n l y i f C a n d C ° ' b e l o n g
t o t h e s a m e p - b l o c k o f S a l , i . e . i f t he y b o ~ h h a v e t h e s a m e
p - c o r e .
A c c o r d i n g t o t h i s w e d e n o t e t h e d i a g r a m o f C a s t h e d i a g r a m o f C
s u c h t h a t n o w 8 . 2 7 r e a d s a s f o l l o w s :
8 . 2 8 T w o o r d i n a r y i r r e d u c i b l e r e p r e s e n t a t i o n s o f t h e c e n t r a l i z e r
o f a p - e l e m e n t o f S b e l o n g t o t h e s a m e p - b l o c k i f a n d o n l y
i f t h e i r d i a g r a m s h a v e t h e s a m e p - c o r e .
T w o c o r o l l a r i e s a r e ( K e r b e r [ I ] , O s i m a [ 4 ] ) :
8 ~ I f ~ i s a p - e l e m e n t o f t y p e ( a l , . . . , a n ) , t h e n CS n .( X ) h a s
o n l y o n e p - b l o c k i f a 1 ~ I a n d p ~ 2 r e s p . i f a 1 ~ 2 a n d p = 2 .
A n a p p l i c a t i o n t o th e c h a r a c t e r t a b l e i s :
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 186/197
181
8 . 3 0 I f B is t h e b l o c k o f S w h i c h c o n t a i n s t h e i d e n t i t y r e p r e s e n -
t a t i o n [ h i, t h e n C a ( x y ) = 0 , V [ a S E B i f a I ~ I ( x a p - e l e m e n t
o f t y p e ( a l , . . . , a n ) ) a n d p ~ 2 r e s p . i f a i ~ 2 a n d p= 2 .
T h e s e r e s u l t s f o l l o w f r o m a r e s u l t o f B r a u e r ( B r a u e r [ 2] , m a i n
t h e o r e m ) , t h a t e v e r y c o l u m n o f t h e g e n e r a l i z e d d e c o m p o s i t i o n m a t r i x
o f a f i n i t e g r o u p G c o n t a i n s n o n v a n i s h i n g e n t r i e s o n l y i n t h e r o w s
o f a c e rt a i n p - b l o c k ( 8 . 3 0 c an b e ob t a i n e d f r o m t h e M u r n a g h a n - N a k a -
y a m a - f o r m u l a a s w e l l ) .
8 . 2 9 s u g g e s t s t h a t w e c o n c l u d e w i t h a h i n t a t a n i m p o r t a n t r e s u l t
o f 0 s i m a ( 0 s i m a [ 4 ]) w h i c h e s t a b l i s h e s t h e c o n n e c t i o n b e t w e e n t h e
p - b l o c k s o f S a n d t h e p - b l o c k s o f t h e c e n t r a l i z e r s o f p - e l e m e n t s
( s ee B r a u e r [ 2] , ( 6 A ) , a l s o C u r t i s / R e i n e r [ I ] , ~ 8 7, 9 0A ) :
8 . 3 1 T h e b l o c k ~ o f C S ~ ( ~ ) w i t h p - c o r e [ ~] d e t e r m i n e s t h e p - b l o c k
B o f S w i t h t h e s a m e p - c o r e I V] .
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 187/197
R e f e r e n c e sm
N . N . A i z e n b e r g : [ I] O n t h e r e p r e s e n t a t i o n s o f t h e w r e a t h p r o d u c t o f
f i n i t e g r o u p s . U k r a i n M a t . ~ . 1 3 , n o . 4 ( 1 9 6 1 ) ,
5-12. (Zbl 109, MR 25)
E . B a y a r : [ 1 ] E i n e ne u e E i n f G h r u n g i n d i e D a r s t e l l u n g s t h e o r i e s y m -
m e t r i s c h e r G r u p p e n . M i t t . m a th . S e m . U n i v . G i e s s e n
8 1 ( 1 9 6 9 ) , 1 - 4 5 . ( Z b l 1 9 7 , ~ R 3 9)
J . L . B e r g g r e n : [ 1 ] F i n i t e g r o u p s i n w h i c h e v e r y e l e m e n t i s c o n j u -
g a t e t o i t s i n v e r s e . P a c i f i c J . M a t h . 2 8 ( 1 9 6 9 ) ,
289- 293. (Zbl 172, MR 39)
R . L . B i v i n s /
O . N . M e t r o p o l i s /
P . R . S t e i n /
M . B . W e l l s :
[ I] C h a r a c t e r s o f t h e s y m m e t r i c g r o u p s o f
d e g r e e 1 5 a n d 1 6 . ~ a t h . T a b l e s A i d s C o m p u t .
(195# ), 212-216. (Z bl 56, ~ 16)
H . B o e r n e r : [ I] R e p r e s e n t a t i o n s o f G r o u p s . N o r t h - H o l l a n d
P u b l i s h i n g C o m p a n y , A m s t e r d a m , 1 9 63 .
[ 2] R e p r e s e n t a t i o n s o f G r o u p s . S e c o n d r e v i s e d e d it i on .
N o r t h - H o l l a n d P u b l i s h i n g C o m p a ny , A m s te r d a m , 1 9 7 @
[ 3] D a r s t e l l u n g s t h e o r i ~ d e r e n d l i c h e n G r u p p e n . E n z y -
k l o p ~ d i e d e r m a t h . W i s s . B a n d I ,I , H e f t 6 , T e i l If.
T e u b n e r - V e r l a g , S t u t t g a r t , 1 9 6 7 .
R . B r a u e r : [ I] O n a c o n j e c t u r e b y N a k a y a m a . T r a n s . R o y . S o c . C a n a d a ,
Sect. III (3) 41 (1947), 11-19. (Zbl 29, MR 10)
[ 2] Z u r D a r s t e l l u n g s t h e o r i e d e r G r u p p e n e n d l i c h e r 0 r d -
nun g II. Math . Z. 72 (1959), 25-46. ~Zbl 93, MR 21)
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 188/197
183
R. Brauer/O. Nesbitt: [ 1 ] On the mod ula r char acters of groups.
Ann als of Math . (2) 42 (1941), 556-590.(Zbl 27, MR 2)
M. Burrow: [I] A generali zation of the Youn g diagram. Can. J. Math.
( 1 9 5 4 ) , 4 9 8 - 5 o 8 . ( Z b l 5 6 , m ~ 1 6 )
[ 2 ] Repres entati on theory of finite groups. A cademic
Press, Ne w York/ London , 1965.
A. Cauchy: [1] Exercis em d'analyse et de physique math~matique.
Band III, Paris 1844.
A.H. Clifford: [ 1 ] Repres entatio ns induced in an invariant sub-
group. Anna ls of Math. (2) 38 (1937), 533-550.
( Z b l I ? )
A.J. Coleman: [1] Induced representations wit h applications to S
and GL(n). Lecture notes prepared by 0.J. Bradley.
Queen's Papers in Pure and Applied Mathematics,
no. ~. Queen's University, Kingston, Ontario,1966. (Zbl 14 1, MR 34)
S. Comet: [I] Improved methods to calculate the characte rs of the
sym met ric group. M ath. Oompu t. I.~ (1960), 104-117.
(Z b l 10 3 , MR 22)
H.S.M. Ooxeter/W.O.J. Moser: [ 1 ] Generators and relations for dis-
crete groups. Springer-Verlag, B er-
lin-GSttingen-Heidelberg 1957.
O.W. Curtis/l. Reiner: [I] Repres entati on theory of finite groups
and associative algebras. Interscience
Publishers, New York 1962.
H.K. Parahat: [I] On the natural repre sentation of the symmetric
groups. Proc. G lasg ow Math. Assoc. ~ (1962),
121-136. (Zbl 107, MR 25)
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 189/197
184
J . S . F r a m e : [ 1 ] O r t h o g o n a l g r o u p m a t r i c e s o f h y p e r o c t a h e d r a l g r o up s .
N a g o y a M a t h . J . 2 7 ( 1 9 6 6 ), 5 8 5 - 5 9 0 . ( Z b l 14 5 , M R 3 3 )
J.S. P r a m e /
G . d e B . R o b i n s o n /
R . M . T h r a l l :
[ I] T h e h o o k g r a p h s o f t h e s y m m e t r i c g r o u p .
C a n a d i a n J . M a t h . ~ ( 1 9 5 4 ) , 3 1 6 - 3 2 4 .
(zbl 5 5 , M R 1 5 )
R . E r u c h t : [ I ] C o r o n a s o f g r o u p s a n d t h e i r s u b g r o u p s , w i t h a n a p p l i ~
c a t i o n t o d e t e r m i n a n t s . ( S p a n i s h ) R e v i s t a U n i o n M a t .
A r g e n t i n a ~ ( 1 9 4 2 ) , 4 2 - 6 9 . ( Z b l 6 1 , M R 4 )
Y. Gtindttzalp: [1 ] ~ be r d i e g e w G h n l i c h e n i r r e d u z i b l e n O h a r a k t e r e d e r
s y m m e t r i s c h e n G r u p p e . M i t t . m a t h . S em . U n i v . G i e s -
sen 8_!I no. 2 (196 9), 1-53. (Zb l 196, MR 39)
B . H u p p e r t : [ I] E n d l i e h e G r u p p e n I . S p r i n g e r - V e r l a g , B e r l i n - G S t t i n -
g e n - H e i d e l b e r g - N e w Y o r k 1 9 6 7 .
H . H u t z e l m e y e r / P . K r a m e r / T . H . S e l i g m a n : [ I ] A n t i s y m m e t r i c s t a t e s o f
t h e c l u s t e r m o d e l a n d t h e i r ~ - p a r t i c l e p a r e n t a g e .
I n t e r n a t i o n a l C o n f e r e n c e o n C l u s t e r i n g P h e n o m e n a i n
N u c l e i . B o c h u m 1 9 6 9 .
O. J o r d a n : [ 1 ] T r a i t ~ d e s s u b s t i t u t i o n s e t d e s ~ q u a ti o n s a l g ~ -
b r i q u e s . G a u t h i e r - V i l l a r s , P a r i s , 1 8 7 0 .
L . K a l o u J n i n e : [ I] S u r le s p - g r o u p e s d e S y l o w d u gr o u p e s y m ~ t r i q u e
du de gr ~ pm. C .R. A cad . Sci. Pa ri s 22__!1 1945 ),
222-224 . (Zb l 61 , MR 7)
[ 2 ] L a s t r u c t u r e d u p - g r o u p e d e S y l o w d u g r o u p e
s y m ~ t r i q u e d u d e g r ~ p 2 . C . R. A c a d . S c i . P a r i s
~ 2 2 ( 1 9 4 6 ) , 1 4 2 4 - 1 4 2 5 . ( Z b l 6 1 , M R 8 )
[ 3] S ur l e s p - g r o u p e s d e S y l o w d u g r o u p e s y m e t r l q u e d u
d e g r ~ p m . (s u i t e c e n t r a l e a s c e n d a n t e e t d e s c e n -
d a n t e . ) C . R . A c a d . S c i . P a r i s 2 2 3 ( 1 9 4 6 ) , 7 0 3 - 7 0 5 .
(MR 8)
[ 4 ] S u r l e e p - g r o u p e s d e S y l o w d u g r o u p e s y me t rl q ue l d u
d e g r 6 p m . ( S o u s - g r o u p e s c a r a c t e r i s t i q u e s , s o u s -
g r o u p e s p a r a l l e l o t o p i q u e s . ) C . R. A c a d . S c i . P a r i s
2 2 4 ( 1 9 4 7 ) , 2 5 3 - 2 5 5 . ( Z b l 3 0 , ~ R 8 )
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 190/197
185
[ 5S L a s t r u c t u r e d e s p - g r o u p e s d e s S y l o w d e s g r o u p e s
s y m 6 t r i q u e s f i n i s . A n n . S c i . E c o l e N o r m . S u p . ( 3)
6 5 ( 1 9 4 8 ) , 2 5 9 - 2 7 6 . ( Z b l 3 4 , M R 1 0 )
[ 6] S u r l a s t r u c t u r e d e s p - g r o u p e s d e S y l o w d e s g r o u -
p e s s y m e t r l q u e s f i n i s e t d e q u e l q u e s g e n e r a l i z a -
t i o n s i n f i n i s d e s o es g r o u p e s . S e m i n a i r e B o u r b a k i
1 9 4 8 / 1 9 4 9 ( Z b l 10 0 )
[ 7] ~ b e r s i n e V e r a l l g e m e i n e r u n g d e r p - S y l o w g r u p p e n
s y m m e t r i s c h e r G r u p p e n . A c t a M a t h . A c a d . S c i . H u n -
gar. ~ ( 1951), 197-2 21. (Zbl 44, MR 14)
A . Ke r b e r : [ I] Z u r m o d u l a r e n D a r s t e l l u n g s t h e o r i e s y m m e t r i s o h e r u n da l t e r n i e r e n d e r G r u p p e n . M i t t . m a t h . S e m . U n i v . G i e s -
sen 6.~8 (1966) , iii +80 8. (Zbl 139, MR 33)
[ 2] Z u r D a r s t e l l u n g s t h e o r i e y o n K r a n z p r o d u k t e n . C a n . J .
Math . 2_~0 (1968), 665- 672. (Zbl 157, MR 58)
[ 3] Z u r m o d u l a r e n D a r s t e l l u n g s t h e o r ie s y m m e t r i s c h e r u n d
a l t e r n i e r e n d e r G r u p p e n I I . A r c h l y d . M a t h . 1 9 ( 19 6 9 ) ,
5 8 8 - 5 9 4 . ( Z b l 1 7 5, M R 3 9 )
[ 4] Z u r D a r s t e l l u n g s t h e o r i e y o n S y m m e t r i e n s y m m e t r i s c h e rG r u p p e n . M i t t . m a t h . S e m . U n i v . G i e s s e n 8_~0 ( 1 9 6 9 ) ,
1-27. (Zbl 167, MR 40)
[ 5] O n a p a p e r o f F o x a b o u t a m e t h o d f o r c a l c u l a t i n g t h e
o r d i n a r y i r r e d u c i b l e c h a r a c t e r s o f s y m m e t r i c g r o u p s .
J . C o m b i n a t o r i a l T h e o r y ~ ( 1 9 6 9 ) , 9 0 - 9 3 . ( Z b l 1 6 5,
M R 3 8 )
[ 6] Z u r T h e o r i e d e r M - G r u p p e n . M a t h . Z . 1 ! ~ ( 1 9 7 0) , 4 - 6 .
( Z b l 1 8 6 , M R 4 1 )
[ 7] Z u e i n e r A r b e i t y o n J . L . B e r g g r e n ~ b e r a m b i v a l e n t e
G r u p p e n . P a c i f i c J. M a t h . ( Z b l 18 2 )
A . K e r b e r / [ I ] O n t h e d e c o m p o s i t i o n n u m b e r s o f s y m m e t r i c a n d
M . H . P e e l : a l t e r n a t i n g g r o u p s . M i t t . m a t h . S e m. U n i v . G i e s s e n
9_!I (1971) , 4 5 - 8 1 .
K . K o n d o : [ I] T a b l e o f c h a r a c t e r s o f t h e s y m m e t r i c g r o u p o f
deg ree 14. Proc . Phys . Mat h. Soo. Jap an (3) 2_~2
( 1 9 4 0 ) , 5 8 5 - 5 9 3 . ( Z b l 23 , M R 2 )
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 191/197
186
[ 2] D e c o m p o s i t i o n o f t h e c h a r a c t e r s o f s o m e g r o u p s I .
P r o c . P h y s . - M a t h . S o c . J a p a n ( 3 ) 2 3 ( 1 9 4 1 ) , 2 6 ~ - 2 7 1 .
(MR 3)
P . K r a m e r / T . H . S e l i g m a n : [ 1] O r i g i n o f R e g g e S y m m e t r y f o r W i g n e r
C o e f f i c i e n t s o f S U ( 2 ) . Z . P h y s i k 2 1 9
( 1 9 6 9 ) , 1 0 5 - 1 1 3 .
M . K r e t z s c h m a r: [ I] G r u p p e n t h e o r e t i s c h e U n t e r s u c h u n g e n z u m S c h a l e n -
m o d e l l I. D i e M a t h e m a t i s c h e T h e o r i e d e s H a m i l t o n -
O p e r a t o r s . Z . f . P h y s i k 1 ~ 7 ( 1 9 6 0 ) , 4 3 3 - 4 5 6 .
[ 2] G r u p p e n t h e o r e t i s c h e U n t e r s u c h u n g e n z u m S c h a l e n -
m o d e l l II. Z a m P r o b l e m d e r T r a n s l a ti o n s i n v a ri -
a n z . Z . P h y s i k I ~ 8 ( 1 9 6 0 ) , 2 8 4 - 3 0 3 .
D . E . L i t t l e w o o d : [ I] I n v a r i a n t t h e o r y , t e n s o r s a n d g r o u p c h a r a c t e r s .
P h i l . T r a n s . R o y . S o c . L o n d o n S e r . A 2 3 9 ( 1 9 4 4 )
3 0 5 - 3 6 5 . ( Z b l 6 0, M R 6 )
[ 2] T h e t h e o r y o f g r o u p c h a r a c t e r s a n d m a t r i x r e -
p r e s e n t a t i o n s o f g r o u p s . O x f o r d : A t t h e C l a r e n -
don Press 1940, 2 nd ed. 1958.
[ 3] T h e c h a r a c t e r s a n d r e p r e s e n t a t i o n s o f i m p r i m i -
t i v e g r o u p s . P r o c . L o n d o n M a t h . S o c . ( 3)
(1956), 251-26 6. (Zbl. 70, MR 17)
A . L o e w y : [ 1 ] ~ b e r a b s t r a k t d e f i n i e r t e T r a n s m u t a t i o n s s y s t e m e o d e r
M i s c h g r u p p e n . J . r e i n e a n g e w . M a t h . I ~ 7 ( 1 9 2 7 ) , 2 3 9 -
254.
J . S . L o m o n t : [ I] A p p l i c a t i o n s o f f i n i t e g r o u p s . N e w Y o r k / L o n d o n :
A c a d e m i c P r e s s 1 9 5 9 .
J . M a l z a n : [ I] R e a l f i n i t e g r o u p s . T h e s i s , U n i v e r s i t y o f T o r o n t o
1969.
H . J . M u n k h o l m : [ I] I n d u c e d m o n o m i a l r e p r e s e n t a t i o n s , Y o u n g e l e m en t s ,
a n d m e t a c y c l i c g r o u p s . P r o c . A m e r . M a t h . S o c.
1 9 , 4 5 3 - 4 5 8 ( 1 9 6 8 ) . ( Z b l 1 55 , M R 3 6)
H . N a g a o : [ 1] O n g r o u p s w i t h t h e s a m e t a b l e o f c h a r a c t e r s a s
s y m m e t r i c g r o u p s . J . I n st . P o l y t e c h n . O s a k a C i t y U n i v .
Ser. A ~ (1957), I-8. (MR 19)
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 192/197
187
T . N a k a y a m a : [ I] O n s o m e m o d u l a r p r o p e r t i e s o f i r r e d u c i b l e r e p r e -
s e n t a t i o n s o f a s y m m e t r i c g r o u p I. J a p . J . M a t h .
17 (19 40 ), 165-184 . (Z bl 61, MR 3)
[ 2] O n s o m e m o d u l a r p r o p e r t i e s o f i r r e d u c i b l e r e p r e -
s e n t a t i o n s o f s y m m e t r i c g r o u p s I I. J a p . J . M a t h .
1'7 (19 41 ), 411-42 3. (Z bl 61, MR 3)
E . N e t t o : [ 1] S u b s t i t u t i o n e n t h e o r i e u n d i hr e A n w e n d u n g e n a u f d i e A l -
g e b r a. T e u b n e r - V e r l a g , L e i p z i g 18 8 2 .
B . N e u m a n n : [1 ] D i e A u t o m o r p h i s m e n g r u p p e d e r f r e i e n G r up p e n . M a t h .
A n n . 1 0 7 ( 1 9 3 2 ) , 3 6 7 - 3 8 6 .
O . O r e : [ I] T h e o r y o f m o n o m i a l g r o u p s . T r a n s . A m e r . M a t h . S o c . 5 1
(19 42) , 15-64. (Z b l 28 , MR 3)
M . O s i ma : [ I] O n t h e r e p r e s e n t a t i o n s o f t h e g e n e r a l i z e d s y m m e t r i c
g r o u p . M a t h . J . O k a y a m a U n i v . ~ ( 1 9 5 4 ) , 3 9 - 5 6 .
(Zbl 58, ~ 16)
[ 2] S o m e r e m a r k s o n t h e c h a r a c t e r s o f t h e s y m m e t r i c
g r o u p I I . C a n . J. M a t h . ~ ( 1 9 5 4 ) , 5 1 1 - 5 2 1 . ( Z b l 58 ,
]~[R 16)
[ 3] O n t h e r e p r e s e n t a t i o n s o f t h e g e n e r a l i z e d s y m m e t r i c
g r o u p I I . L a t h . J . O k a y a m a U n i v . ~ ( 1 9 5 6 ) , 8 1 - 9 7 .
(Zbl 72, MR 18)
[ 4] O n t h e g e n e r a l i z e d d e c o m p o s i t i o n n u m b e r s o f t h e sy m -
met ric group. J. ~ath. Soc. J apa n 2_~0 (1968), 289- 296.
(MR 36)
[ 5] O n t h e g e n e r a l i z e d d e c o m p o s i t i o n n u m b e r s o f t h e a l -
t e r n a t i n g g r o u p . ( J a p a ne s e ) S y m p o s i u m o n G r o u p T h e o r y ,
K y o t o U n i v . , 1 9 6 8 , 5 1 -5 5 .
T . O y a m a : [ I] O n t h e g r o u p s w i t h t h e s a m e t a b l e o f c h a r a c t e r s a s
a l t e r n a t i n g g r o u p s . O s a k a J . M a t h . 1 ( 1 9 6 & ) , 9 1 - 1 0 1 .
(Zbl 139, MR 29)
M . H . P e e l : [ I] O n t h e s e c o n d n a t u r a l r e p r e s e n t a t i o n o f t h e s y m m e t r i c
grou ps. Gla sg ow Math . J. 1_~0 (1969), 25-37. (Zbl 175,
] ~ 3 9 )
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 193/197
1 8 8
[ 2] H o o k r e p r e s e n t a t i o n s o f t h e s y m m e t r i c g r o u p s .
( t o a p p e a r i n t h e G l a s g o w M a t h . J .)
S . P i o c a r d : [ 1] S u r l e s b a s e s d u g r o u p e s y m 6 t r i q u e e t l e s c o u p l e sf
d e s u b s t i t u t i o n s q u i e n g e n d r e n t u n g r ou p e r e g u l l e r .
M e m . U n i v . N e u c h ~ t e l , T o m e I__9 ( 1 9 4 6 ) . ( Z b l 6 1 , M R 8 )
[ 2] S u r l e s b a s e s d u g r o u p e s y m e ~ r i q u e I I. P a r i a , L i b -
r a i r i e V u i b e r t , 1 9 48 . ( Z b l 3 1 , N R 1 0)
[ 3] S u r l e s b a s e s d ~ s ~ r o u p e s d ' o r d r e f i n i . M e m . U n i v .
N e u c h ~ t e l , T o m e ~ ( 1 9 5 7 ) . ( Z b l 7 7 , ~ 2 0 )
G . P 6 1 y a : [ I] K o m b i n a t o r i s c h e A n z a h l b e s t i m m t m g e n f o r G r u p p e n, G r a -
p h e n u n d c h e m i s c h e V e r b i n d u n g e n . A c t a ma t h . U p p s a l a
6_~8 (19 37 ), 14 5- 25 4.
B . M . P u t t a s w a m a i a h : [ I] G r o u p r e p r e s e n t a t i o n s ( a l t e r n a t i n g a n d g e -
n e r a l i z e d s y m m e t r i c g r o u p s ) . T h e s i s , U n i v e r -
s i t y o f T o r o n t o 1 96 3.
[ 2] U n i t a r y r e p r e s e n t a t i o n s o f g e n e r a l i z e d s y m -
m e t r i c g r o u p s . C a n . J . M a t h . 2!I ( 1 9 6 9 ) ,28-38. (Zbl 169, MR 38)
B . M . P u t t a s w a m a i a h / G . d e B . R o b i n s o n : [ I] I n d u c e d r e p r e s e n t a t i o n s
a n d a l t e r n a t i n g g r o u p s . C a n . J . M a t h . 1 6
( 1 9 6 4 ) , 5 8 7 - 6 0 1 . ( M R 2 9 )
A . Ra d z i g : [ I] D i e A n w e n d u n g d e s S y l o w ' s c h e n S a t z e s a u f d i e s y m m e -
t r i s c h e u n d d i e a l t e r n i r e n d e G r u p p e . D i s s . B e r l i n
1895.
G . d e B . R o b i n s o n : [ I] A g e o m e t r i c a l s t u d y o f t h e h y p e r o c t a h e d r a l
g r o u p . P r o c . C a m b r i d g e P h i l o s . S o c . 2 6 ( 1 9 3 0)
9 4 - 9 8 .
[ 2] O n a c o n j e c t u r e b y N a k a y a m a . T r a n s . R o y . S o c .
Ca na da Sect. III (3) 4_!I (1947 ), 20-25 .
(Zbl 29, MR 10)
[ 3] O n t h e d i s j o i n t p r o d u c t o f i r r e d u c i b l e r e -
p r e s e n t a t i o n s o f t h e s y m m e t r i c g r o u p . C a n .
J . M a t h . ! ( 1 9 4 9 ) , 1 6 6 - 1 7 5 . ( M R 1 0 )
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 194/197
189
[4] Induced representations and invariants. Oan.
J. Math. ~ (1950), 334-34 3. (Zbl 39, MR 12)
[5] Repre senta tion theory of the symmetric group.
Unive rsity of Toronto Press, Toro nto 1961.
[6] Modu lar represen tations of 8 . Can. J. Math.
16 (1964), 191-203. (Zbl 11 7, ~R 28)
G. de B. Robinson/0.E. Taulbee: [I] On the modul ar represen tations
of the sym metri c group VI. Proc. Nat. Acad.
Sci. US A 41 (1955), 596-598. (Zbl 66, MR 17)
A. Scholz: [I] Ein Beit rag zur Zusammen setzung e ndlicher Gruppen.
Mat h. Z. 32 (1930), 187-189.
G.M. Seitz: [I] M-Group s and the supersolv able residual. Math. Z.
110 (1969), 101-122.
P.R. Smith: [1] The use of plethy sm in the study of configurati on of
equiv alent electrons. M. Sc. thesis, Un ive rsi ty of
Canterbury, Ne w Zealand 1967.
P.R. Smith/B.G. Wybourne: [I] Selection rules and the decomp ositio n
of the Krone cker square of irreducible represen -
tations. J. Math. Phys. ~ (1967), 2434-244 e.
[2] Ple thy sm and the theor y of comp lex spectra. J. Math.
Phys. ~ (1968), 1040-1051.
W. Specht: [1] Ein e Verallge meine rung der symmetri echen Gruppe.
Schr ifte n Ber lin I (1932), 1-32. (Zbl 4)
[2] Eine Verall gemei nerung der Permutation sgruppen. Math.
Z. 3 7 (1933), 321-341. (Zbl 7)
O.E. Taulbee: [I] Modu lar repr esentati ons of the symmetric group.
Thesis, Michig an State Unive rsity 1957.
A.J. Weir: [I] The 8ylo w subgroups of the symme tric groups. Proc.
Amer . Math . Soc. 6 (1955), 534 -541. (Zbl 65, MR 17)
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 195/197
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 196/197
8/3/2019 (Lecture Notes in Math, No 240)Adalbert Kerber-Representations of Permutation Groups Representations of Wreath Products and Applications to the Repres…
http://slidepdf.com/reader/full/lecture-notes-in-math-no-240adalbert-kerber-representations-of-permutation 197/197
192
L i t t l e w o o d - R i c h a r d s o n - r u l e
L i t t l e w o o d ' s t h e o r e m o f
c o n j u g a t e s
M - g r o u p
~ u r n a g h a n - N a k a y a m a - f o r m u l a
N a k a y a m a ' s c o n j e c t u r e
O d d p e r m u t a t i o n
o r d e r o f a c y c l e
P - c o m p o n e n t
p - e l e m e n t
84 .
125
111
80
131
11
6
168
8
S e l f a s s o c i a t e d p a r t i t i o n 2 0
- Y o u n g - d i a g r a m 2 0
s i m i l a r p e r m u t a t i o n g r o u p s 2 9
s t a n d a r d - c o n j u g a t o r 14
s t a n d a r d - t a b l e a u 71
s y m b o l s 5
s y m m e t r i c g r o u p 5
- - , g e n e r a l i z e d 3 9
s y m m e t r i z e d o u t e r p r o d u c t s
( g e n e r a l ) 1 0 2
( o f i r r . o r d i n a r y
r e p r . o f S n ) 1 1 7
s y m m e t r y 3 9