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Rare top decays in Extended

Models Ricardo Gaitán Centro de Investigaciones Teóricas, Facultad de Estudios Superiores - Cuautitlán,

Universidad Nacional Autónoma de México, (FESC-UNAM).

Omar G. MirandaDepartamento de Física, Centro de Investigación y de Estudios Avanzados del

IPN, (CINVESTAV).

Luis G. Cabral-RosettiDepartamento de Posgrado, Centro Interdisciplinario de Investigación y Docencia

en Educación Técnica, (CIIDET).

Phys. Rev. D 72, 034018 (2005)

X Mexican Workshop on Particles and FieldMorelia Mich., November 7-12, 2005.

R. GAITÁN O. G. MIRANDA L. G. CABRAL ROSETTI

Rare top decays in Extended Models

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OVERVIEW

1) Introduction

2) Alternative left-right symmetric Model (ALRM)

3) Top and Higgs decays in the ALRM a) Constraining the top-charm mixing angle b) The decay: t → H° + c c) The decay: t → H° +

4) Results and Conclusions

c̄



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1) Introduction

The top quark was regarded as an essential ingredient of the Standard Model (SM) of particle physics. Its existence, and many of its properties, are determined by the following requirements: theoretical consistency of the Standard Model gauge theory (anomaly cancellations), consistency of b quark measurements with SM predictions, and consistency of precisions measurements with the SM.

The top quark mass, which is measured at CDF and D0 to be approach 174 GEV´s,is not predicted in the SM, but is restricted by precision electroweak measurements. The fact that the top quark is much heavier than the other quarks gives it a special role in electroweak symmetry breaking.

Top quark properties:

2| |

3temQ e

Weak isospin partner of b quark 3

1

2tT

Color triplet

Spin- 1

2



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1) Introduction

The mixings will affect the couplings to the neutral current (NC) and the charged current (CC) of the known neutral states, and then could be restricted by the precision tests of the SM.

ORDINARY AND EXOTIC FERMIONS

Different extensions of the STANDAR MODEL (SM), such as the Models withLeft-Right Symmetry, SO(10) and E(6), predicts the existence of new fermions with exotic SU(2) X U(1) assignments.In addition to direct production, these new fermions can manifest themselves through their mixing with the known quarks and leptons.



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1) Introduction

Standard Model

, ,

, ,

e

L L L

L L L

e

u c t

d s b

doublets in SU(2) singlets in SU(2)

, , ,

, , ,

, ,

R R R

R R R

R R R

e

u c t

d s b

There are several possibilities for new fermions. The sequential fermions are repetitions of the known fermions, with canonical (L-doublets , R-singlets) SU(2) X U(1) assignments. The mirror fermions are L-handed singlets and R-handed doublets of SU(2). The vector doublets concern to new quarks o leptons where the L and R-handed components are SU(2) doublets. The vector singlets are new particles for which L and R are SU(2) singlets . Also, there are SU(2)-singlet Weyl. Finally, one can introduce exotic electric charge or color assignments.



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1) Introduction

MIXING WEAK-HEAVY

Vectors for the ordinary weak eigenstates and exotic, left and right are grouped in the column vector:

00

0

( )

ord

ex L R

n

Vectors for the light mass eigenstates (standard) and heavy are grouped in the column vector:

( )

l

h L R

n

The relation between weak eigenstates and mass eigenstates will be given through

0( ) ( )L R L Rn Un

with( )

( )

L R

L R

A EU

F G

, U U I

From the unitarity of U is obtained:

where I is the identity matrix, i.e.

A A F F A A E E I 0

0

II

I



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1) Introduction

NEUTRAL INTERACTIONS WITH FLAVOUR CHANGE OF THE TOP

The next generation of high energies colliders, planned or in construction, will probe the Standard Model (SM) with high precision, and they will explore higher energies in the new physic research.

The new Physics could be manifest in two ways: through direct signals including the production of new particles or departure of the SM predictions for known particles.

The quark top plays an important role in the search of departures of the SM predictions for two reasons:

1) Because their great mass, the radiative corrections that include new particles, frequently are more important than for the light fermions. 2) Their great mass (approximately 178 GeV’s) suggest that it may be plays

an special role in the electroweak symmetry breaking.



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1) Introduction

Quarks top could be copiously produced in LHC and in colliders e+e- of high energy such as TESLA. With these big probes, we will to have more precise measures of their coupling to probe the SM.

Is very important the study of the flavor changing neutral currents with (FCNF) including the quark top. The quark top decays induced by FCNC are extremely rare events in the SM.

In the ME,

13( ), ( ), ( ) 10BR t c BR t c Z BR c H 13( ) 10BR H t c

Considering physics beyond the SM, there are new possibilities that could change radically the pessimist prospectus for the FCNC decays that include a Higgs boson and a quark top

Two Higgs Doublets Model (2HDM)Minimal Supersymmetric Standard Model (MSSM)

Example:



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LBRL USUSU )1()2()2(

00

0

0000

0

00

0

0

000

0

00

ˆ,ˆ,ˆˆˆ;,,

ˆ,ˆ

ˆˆ;,

iLiL

Ri

iiRiRiR

Li

iiL

iL

Ri

iiRiR

Li

iiL

dud

uQdu

d

uQ

ee

lee

l

vv ˆ

0

2

1ˆ;0

2

1

The gauge group of ALRM is:

cos)ˆ(sin)(2ˆ

sin)ˆ(cos)(200

00

veveH

veveH

Fermionic sector:

The Higgs fields:

where denotes the neutral Higgs mixing angle.

The neutral and massive Higgs bosons are:



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Higgs boson and quarks interaction

matrix.Paulithe

with,ˆ~̂and~are

~̂~fieldsconjugateThematrices.unknown

areand,ˆ,and3,2,1,where

..ˆˆˆ~̂ˆˆ

ˆˆˆˆ~

2*

2*

2

)()()(

000000

000000

ii

ji

chuudduQ

dQuQdQ

udij

udij

udij

jRiLuijjRiL

dijjLiR

uij

jLiRdijjRiL

uijjRiL

dij

qY

L



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..)cosˆsin(22

ˆ

)sinˆcos(22

ˆ

chHHFFM

mg

HHM

mAA

g

RRR

W

fL

RW

fLLL

fY

L

The tree-level interactions of neutral Higgs bosons H and H with the lights fermions are given by:^

level. at tree FCNC havecan we

matrices, theofy nounitarit the to thanks that,seecan weequations, last two Fron the

ly.respective,)1(and,)2(,)2(ofgeneratorstheareand,ˆ,where

,ˆ2

´,ˆˆ,

33

33,

a

LBRLaa

aaa

aaaRLa

a

A

USUSU

A

Z

Z

ggg

YTT

UY

TTU c.n.- L

The neutral current in terms of the mass eigenstates, including the contributions of the neutral gauge boson mixing, can be written as follows :



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3a) Constraining the top-charm mixing angle

53.032

32323232

32

2

32

2

,

)(;)(

41

41

where,)(

RRR

LLL

RLAV

AVctZ

AAAA

sr

cs

r

scg

tZggccse

W

W

W

W

WW

L

1.032

From BR( t → Z + c) and comparing with the experimental limit, we obtain that

FC coupling of Z to top-charm quarks

From

We obtain that:

)1)(1( 2233

2

32



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3b) The decay: t → H° + c

2/12222

22222

320

216

cos)(

cHtcHt

Hctt

F

mMmmMm

Mmmm

GcHt

LW

t PMmg

cos2

32

)()(

)(0

0

WbtcHt

cHtBR



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3b) The decay: t → H° + c



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3c) The decay: H°→ t +

2/12222

2223

22320

28

cos3)(

tcHctH

ctHH

tF

mmMmmM

mmMM

mGctH

c̄

quarks.for3and

leptonsfor1,)/(where

4124

cos)(

2

2/3222

0

f

fHff

fffHfF

f

C

CMm

MmGCffH



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3c) The decay: H°→ t +

2

2/123

0

)/(with

4128

cos)(

HWW

WHF

MM

MGWWH

c̄

22

2

2/1

4

22430

/and

)/(with

1241

41216

cos)(

crstrsccX

MM

M

XMMGZZH

WWWWW

HZf

ZZ

ZZ

WHF



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3c) The decay: H°→ t + c̄



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4) Results and Conclusions

32

)( cHtBR 410

1) The model allows relatively big values of

2) The could be of order of , which is at the reach of LHC.

3) The may reach a value of order and can also be an useful channel to look for signals of new physics in LHC.

310

)( ctHBR

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