Dynamical EWSB and Fourth Generation

1
Dynamical EWSB andFourth Generation
2009.10.28_at_KEK

• Michio Hashimoto
• (KEK)

M.H., Miransky, 0901.4354.
M.H., Miransky, in preparation.
Mt. Tsukuba
2
Introduction

• Standard Model (SM) is phenomenologically
  successful.
• However, several points are theoretically
  unnatural

Fine-tuning
No explanation for the mass hierarchy
Why 3 generation?
The KM theory requires 3 or more.
Why not?
The 4th generation
3
?What is it for?
Dynamical Electroweak Symmetry Breaking
?The LHC has a discovery potential for the
chiral 4th family at early stage.
? B Physics, EW Baryogenesis, etc.
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contents
Introduction
Status of the 4th generation model
?
Super heavy quarks and multi-Higgs doublets
M.H., Miransky, in preparation.
M.H., Miransky, 0901.4354.
Summary
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Constraints for the 4th family
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? constraints for the masses
For quarks,
CDF, Public Note 9759
Summer, 2009
CDF, Public Note 9446
July, 2008
For leptons,
Particle Data Group (PDG) 2008
(invisible case)
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? Number of light neutrinos
? Z boson invisible width at LEP
by invisible Z width (PDG2008)
? Is it proof of the 3 generation?
is allowed !!
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? Constraints from the oblique corrections
G.D.Kribs, T.Plehn, M.Spannowsky, T.M.P.Tait,
PRD76(07)075016.
1 Higgs 4th family
viable parameter region
LEP EWWG 68 and 95 C.L. constraints
? LEPWG,
? PDG2008,
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The LHC can discover or exclude b
at early stage.
(significance)
For example,
(exclusion 95 C.L.)
talk by Kai-Feng Chen (NTW), the CMS
collaboration
August, 2009
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Perturbative unitarity bound
N.B.
Chanowitz, et. al., PLB78(78)285 NPB153(79)402.
It will be a milestone for the experiments.
? The quark masses above 1TeV will be constrained
by gg ? ZZ.
Chanowitz, et. al., PLB352(95)376.
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? The generation structure is a mystery in the
particle physics.
The chiral 4th generation has not yet been
excluded by experiments.
Probably, the LHC will answer the question.
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If the 4th family may exist, what is interesting?
Dynamical Electroweak Symmetry Breaking
The 4th generation quarks can be closely
connected with the DEWSB through their
condensations.
The yukawa coupling runs very quickly and
reaches the Landau pole at most several tens TeV.
This is a signal for the DEWSB!!
(TeV)
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Superheavy quarks and multi-Higgs doublets
M.H., Miransky, 0901.4354 in preparation.
? The yukawa couplings have the Landau pole, so
that the theory is effective only up to this
scale lt O(10TeV).
?The Nambu-Jona-Lasinio description is applicable
in low energy.
? The point is that the masses of t, b and t
are O(v246GeV).
? Besides t and b condensations, the top
condensation also contributes to the EWSB.
Multiple Higgs doublet model
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Three Higgs doublet model
M.H., Miransky, in preparation.
Model
low energy effective theory _at_ composite scale
kinetic term for the fermions
We consider only t, b and t.
kinetic term for the gauge bosons
Nambu-Jona-Lasinio couplings effectively
induced in low energy
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How to get them
Topcolor gauge boson exchange
topcolor instanton
flavor changing neutral interaction between t-t
We dont know a natural candidate of the origin.
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Auxiliary Field Method
Let us introduce the auxiliary field,
etc.
yukawa int.
Higgs mass terms
If
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?The low energy effective theory _at_ EWSB scale
The Higgs bosons get the kinetic terms and
quartic couplings.
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? Higgs potential _at_ 1/Nc leading approximation
_at_ 1/Nc LO
Higgs quartic coupling --- 2 Higgs part 1 Higgs
part
(21)-Higgs doublet model
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? The RGE approach is more convenient.
NJL model RGE compositeness conditions
Bardeen, Hill, Lindner, PRD41(90)1647.
(composite scale)
Compositeness conditions
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? Even in the RGE analysis, the (21)-Higgs
structure is kept, if we ignore the EW
1-loop effect. The quartic term is then
written as
? The EW 1-loop diagram yields, for example,
When we consider the full 1-loop RGE, we should
analyze a general 3 Higgs model, instead of the
(21)-Higgs.
? 45 parameters in the quartic couplings
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Numerical Analysis

• We have 8 theoretical parameters

composite scale (Landau pole) of t and b
composite scale (Landau pole) of the top
The physical quantities are
3 Higgs doublets
CP even Higgs -- 3
CP odd Higgs -- 2
charged Higgs -- 22
VEV -- 3
etc.
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? Definition of the angles of the VEVs
? It is natural to take similar composite scales.
? Owing to yt yb, the T parameter constraint
implies
Also,
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By using
we approximately obtain
We here took
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?It is convenient to take the following
parameters
? The outputs are
decay widths of
yukawa couplings between the fermions and the
Higgs bosons
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We calculate the mass spectrum by using the RGE
RGE for the (21)-Higgs doublets compositeness
conditions
and
for various
The bold curves are for
The dashed curves are for
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The mass spectrum of the Higgs bosons for various
and
We also used
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How about the Higgs contributions to the
S,T-parameter
?
constraint is potentially dangerous.
bounds yield the constraint to
and it corresponds to
TeV
for
TeV
is small.
and
The sensitivity of
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? The 4th generation quarks drastically increases
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? An example for the scenario with
Inputs
Outputs
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yukawa couplings
Decay width into WW, ZZ
Enhancement of Higgs production
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? An example for the scenario with
Inputs
Outputs
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yukawa couplings
Decay width into WW, ZZ
Enhancement of Higgs production
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Summary and discussions

• There exists an allowed parameter region for
• the 4th generation model. Probably, the LHC
  will answer to this problem.
• If the 4th generation exist, the t and b will
  be closely connected with the EWSB. The top quark
• also contributes to the EWSB.
• The dynamical model with the 4th generation
  naturally yields multi-Higgs doublets.
  We analyzed the (21)-Higgs model.

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In Progress
Decay mode of the Higgs bosons
Branching ratio of the Higgs
etc.
Under construction
Lepton sector Majorana neutrinos etc.
Thank you,