Emergent EWSB with Composite W,Z

Tony GherghettaUniversity of Melbourne

Planck 2009, May 25, 2009

[with Yanou Cui and James Wells (to appear)]

1Monday, 25 May 2009

Outline

• Introduction/Motivation

• Emergent EWSB

• Phenomenology

• Conclusion

2Monday, 25 May 2009

5D metric

Introduction What is the origin of mass?

1. Higgs mechanism [Guralnik, Hagen, Kibble `64; Englert, Brout `64; Higgs `64]

Higgs boson:

x !H"

!H"

W, Z-boson:

Fermion: mf ! !"H#

• Elementary fermion and W, Z boson masses

• WW scattering

Bad high-energy behaviour

But, spin-0 Higgs boson A(E) ! constantE ! "

A(E) !g2E2

32!m2

W

E ! "

vacuum expectation value

mW,Z ! g"H#

W, Z, f W, Z, f

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5D metric

e.g. QCD:

2. Strong dynamics

proton: mP ! !QCD

strong coupling at

vector-mesons:

!0,±

m! ! !QCDe.g. SU(2) isospin-triplet

• Hadron mass spectrum

In fact, hidden local gauge symmetry! [Bando, Kugo,Uehara, Yamawaki, Yanagida 1985]

• No Unitarity violation

scattering

chiral Lagrangian QCD Lagrangian

!!

!QCD = e!

8!2

g2bi MP

! !

!!

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Can one generate mass in the Standard Model with strong dynamics?

YES, but not easy...

Use AdS/CFT correspondence! [Maldacena, 97; Gubser, Klebanov, Polyakov, 98; Witten 98]

Question:

Effective 4D chiral Lagrangian of composite

W, Z, fermions

5D Lagrangian in warped dimension!

[Randall, Sundrum 99]

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AdS/CFT dictionary

5D AdS

UV IR

y

5th coordinate

Large N, strongly coupled 4D CFT

UV

IR

4D energy scale

E

[Arkani-Hamed, Randall, Porrati 00; Rattazzi, Zaffaroni 00; Perez-Victoria 01]

IR brane breaks conformal symmetry

Generates mass!(2)

(1)

(0)

.

.

.

KK modes OR composite states of dual theory!

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UV(IR) localized field

But,

Separate lightest KK mode from rest of tower with brane kinetic terms!

• Heavy KK modes

• Massless mode

Break EW symmetry at Planck scale!

(2)

(1)

(0)

.

.

.

(2)

(1)

(0)

.

.

.

W1,2,3 B

Degenerate masses

m0 = 0

KK spacing(2)

(1)

(0)

.

.

.

} light resonances!

[Carena, Ponton, Tait, Wagner 2002; Davoudiasl, Hewett, Rizzo 2002]

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5D Model [Cui,TG, Wells, to appear]

X

composite

UV IR

EW symmetry breaking

W, Z

SU(2)L ! U(1)Y

SU(2)L ! U(1)YU(1)EM

5D action:

= boundary kinetic term coefficients!Q, !L, !Y

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5D metric

Mass spectrum:

Boundary conditions:

Obtain:

mIR = TeVFor:

mZ !

!

2

!Lk+

2

!Qk(1 + g2L5

/g2Y 5

)mIRmW !

!

2

!LkmIR

m! = 0

!Qk ! 500, !Lk ! 310, !Y k ! 0.1

mW ! 80.4 GeV, mZ ! 91.2 GeV

(mKK ! 2 TeV)

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0.0 0.2 0.4 0.6 0.8 1.0z! zIR

0.01

0.02

0.03

0.04

0.05

0.06

f1"z#

W

Z

W, Z, photon profiles

NB: Boundary kinetic terms introduce discontinuity at endpoints.

!(not to scale)

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5D metric

Composite W, Z but elementary photon!

Dual 4D interpretation

EWSB emerges at IR scale

“Emergent” EWSB

UV localized field

CFT bound state

elementary “source” state

IR localized field

IR

!R0 y

!UV e!ky

UV

IR

!R0 y

!UV e!ky

UV

!

.

.

.

!

.

.

.

.

.

.

W Z

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5D metric

Fermion masses

• Add UV boundary fermion masses

Assume universal bulk fermion profile

X

UV IR

mfW, Z

!f

Froggatt-Nielsen mechanism on UV brane generates fermion mass hierarchy

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Electroweak constraintsAssume fermions on IR brane

But depends on fermion details....

• S parameter

S ! 0.1, T ! 0.02!Lk ! 1000, !Qk ! 1700, !Y k ! 0.2

mIR ! 1.8 TeV

Matching at IR brane requires: ! = brane thicknessg2

5k !

425

1 + !/!

Custodial symmetry in limit • T parameter !Y ! 0, !Q ! "

i.e. same boundary condition for AL1,2,3

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5D metric

Composite W,Z boson

Interestingly, in large N theory there are no partons inside hadrons!

WW scatteringMomentum dependent

form factor

[Polchinski-Strassler 02]

i.e. composite W, Z bosons are unlike vector-mesons in QCD!

Possible deviation in W, Z-boson vertices at LHC(in progress)

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Example form factor:

1.000.500.200.100.050.02p zIR

0.500

0.100

0.050

0.010

0.005

0.001

FWWZ!p"

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Conclusions• Generate W, Z boson mass from strong

dynamics, not Higgs mechanism

• Electroweak symmetry breaking “emerges” at IR scale

• Consistent with electroweak precision tests (S, T parameters)

• Composite W, Z bosons lead to deviations in vertices at LHC

16Monday, 25 May 2009