Emergent EWSB with Composite W,ZEmergent EWSB with Composite W,Z Tony Gherghetta University of...
Transcript of Emergent EWSB with Composite W,ZEmergent EWSB with Composite W,Z Tony Gherghetta University of...
Emergent EWSB with Composite W,Z
Tony GherghettaUniversity of Melbourne
Planck 2009, May 25, 2009
[with Yanou Cui and James Wells (to appear)]
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Outline
• Introduction/Motivation
• Emergent EWSB
• Phenomenology
• Conclusion
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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
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