compact - math.utah.edu
TRANSCRIPT
G- - connected compactt
lie group
q : GxT -2 G-
ie ( gatt = gt g-I
y is differentiableie (Gat) is compactsubset of Ct , i.e .
y (G-XT) is closed -
claim : yj .
It is enough to provethat y (a- xT) is open in G-since G is connected
.
I
Froot big induction in2
dim G - dimT 30
If dim G- = dim F ⇒ G-=T
y in a projection .
The statement is true .
Can assume that dim G - dimTM.
To show that q ( GxT) is open
it is enough to show that it is
a neighborhood of gt g-'= 4cgF)
for any g EG and tfT .
Since InHg ) is an automorphismof G , it is enough to showthat y l G xT) is a neig
'
bar hood
of t for anyt ←T .
3
Let It be the centralizer
of tH - { he G- l ht -- th}
11
{ he G- / tht"= h }
11
{ he a- I Int H) (h) = h }equalizer of Intlt) and id .
⇒ It is a Lie subgroupHH) = { 3 c- LlG) lad It) 151=3 }Ho - identity componentof H
.4
Clearly , TCH .SinceT is a maximal
torus in .G,it is a maximal
for us in Ho
Let Z be the center ofG-
. There are two optionsL or t¢⑦
⇒ H = G- ⇒ Ho = G .
Let T'be another maximal torus
in G.
Then T'
= hThi'
for some h EG .
Since teZ,teT implies
that t =htti'ET
'.
t is in all max .ton
.
5-
Let Ge Uf) . There ' IR q is
in a maximal abelian Lie sibalgebra ofUG) ⇒ exp } is in a maximal
torus T"
.
t . apes a- T"
.=kTk- 'c y(a-xD .
{ t . apes l -GE UG) 3 is a
neigh . oft ⇒ y (Gxt)is a neigh . of t .
'
tee then we must have
LCH) FL (G) .Otherwise
,
we would have'UH ) =L(G)
it would be open in G- .6
Since G- is connected⇒ It = ft.Hence dim Ll it) - dim L ( G) .
\
,
dim It a dimeG-
dim Ho - dim T s dim G - dint
By induction .
-
'
'
H.xT → H
.is surjective .
⇒
y (a- xT) = y (a- x Ho)y
'
n G- x Ho→ G-
41g ,h ) -- gh g-
'
.
^
T : G- x H. → G-
>
have to prove that this is a
submersion at ( lat) .
Equivalent( §,hi ) 1-5 upB) heap C- as )
is a submersion at ( O,t) .
⇐ L (G) x LtHo) z les ,z)iQ> exp tap in) exp f
- es)is a submersion at co ,o) .
( { , y ) '→ E' erupts) t.expeye.pt 's)is a submersion at lo
,O)
.
G,n)→ ap fad 3) up in) eye testis a submersion at co
,o) . I
8The differential of this map isGm) '→ ANE't est y - § =
- HADLEY -I)Gt n .
( (G) has a natural G - invariant
inner productLCG) = LI Ho) to LIHo)
-
t
ku (Ad KY - I) Im 't AdH -I)Hence
, by the formula forthe differential , we seethat it is surjective .
Hence, y is a submersion
at Kitt, image of y is
a neigh for hood of t .
This implies that9
y (G XT) is a neighborhoodof t .
⇒ eCGXT) is open and
q is surjective .
connectedtheorem .
Let G be a compact^
Lie group . Then
exp :UG)→ G-
is surjective .
theorem ..Let G be a
connected compact Lie
group .
Then away gc- G-
is in a maximal torus
T in G .