Dynamical EWSB and Fourth Generation Michio Hashimoto (KEK) 2009.10.28@KEK Mt. Tsukuba M.H.,...
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Transcript of Dynamical EWSB and Fourth Generation Michio Hashimoto (KEK) 2009.10.28@KEK Mt. Tsukuba M.H.,...
Dynamical EWSB andFourth Generation
Michio Hashimoto
(KEK)
2009.10.28@KEK
Mt. Tsukuba
M.H., Miransky, 0901.4354.
M.H., Miransky, in preparation.
Introduction• Standard Model (SM) is phenomenologically successful.
• However, several points are theoretically unnatural:
Fine-tuning
Why 3 generation?
No explanation for the mass hierarchy
Why not?
The 4th generation
The KM theory requires 3 or more.
★What is it for?
Dynamical Electroweak Symmetry BreakingDynamical Electroweak Symmetry Breaking
★The LHC has a discovery potential for the chiral 4th family at early stage.
◎ B Physics, EW Baryogenesis, etc.
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
Constraints for the 4th family
◎ constraints for the masses
For quarks,
CDF, Public Note 9446
CDF, Public Note 9759
Summer, 2009
July, 2008
Particle Data Group (PDG) 2008
For leptons,
(invisible case)
★ Z boson invisible width at LEP
by invisible Z width (PDG2008)
◎ Is it proof of the 3 generation?
is allowed !!
◎ Number of light neutrinos
◎ Constraints from the oblique corrections
LEP EWWG 68% and 95% C.L. constraints
viable parameter region
● PDG2008,
● LEPWG,
1 Higgs + 4th family
G.D.Kribs, T.Plehn, M.Spannowsky, T.M.P.Tait, PRD76(‘07)075016.
The LHC can discover or exclude b’ at early stage.
For example, (significance)
(exclusion 95% C.L.)
talk by Kai-Feng Chen (NTW), the CMS collaborationAugust, 2009
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.
◎ The generation structure is a mystery in the particle physics.
Probably, the LHC will answer the question.
The chiral 4th generation has not yet been excluded by experiments.
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.
(TeV)
The yukawa coupling runs very quickly and reaches the Landau pole at most several tens TeV.
This is a signal for the DEWSB!!
Superheavy quarks and multi-Higgs doublets
◎ The yukawa couplings have the Landau pole, so that the theory is effective only up to this scale < O(10TeV).
★ Besides t’ and b’ condensations, the top condensation also contributes to the EWSB.
★The Nambu-Jona-Lasinio description is applicable in low energy.
M.H., Miransky, 0901.4354; in preparation.
○ The point is that the masses of t’, b’ and t are O(v=246GeV).
Multiple Higgs doublet model
Model
kinetic term for the fermions
kinetic term for the gauge bosons
Nambu-Jona-Lasinio couplings effectively induced in low energy
Three Higgs doublet model
low energy effective theory @ composite scale
M.H., Miransky, in preparation.
We consider only t’, b’ and t.
Topcolor gauge boson exchange
topcolor instanton
flavor changing neutral interaction between t’-t
We don’t know a natural candidate of the origin.
How to get them:
Auxiliary Field MethodLet us introduce the auxiliary field,
etc.
If
yukawa int.
Higgs mass terms
◎The low energy effective theory @ EWSB scale
The Higgs bosons get the kinetic terms and quartic couplings.
★ Higgs potential @ 1/Nc leading approximation
@ 1/Nc LO
Higgs quartic coupling --- 2 Higgs part + 1 Higgs part
(2+1)-Higgs doublet model
○ The RGE approach is more convenient.
NJL model = RGE + compositeness conditionsBardeen, Hill, Lindner, PRD41(‘90)1647.
(composite scale)
Compositeness conditionsCompositeness conditions
◎ Even in the RGE analysis, the (2+1)-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 (2+1)-Higgs.
45 parameters in the quartic couplings
Numerical Analysis
• We have 8 theoretical parameters;
The physical quantities are
composite scale (Landau pole) of t’ and b’ composite scale (Landau pole) of the top
3 Higgs doublets: CP even Higgs -- 3
CP odd Higgs -- 2charged Higgs -- 2+2
VEV -- 3 etc.
◎ 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,
By using
we approximately obtain
We here took
◎It is convenient to take the following parameters:
★ The outputs are
decay widths of
yukawa couplings between the fermions and the Higgs bosons
We calculate the mass spectrum by using the RGE:
RGE for the (2+1)-Higgs doublets + compositeness conditions
and for various
The bold curves are for
The dashed curves are for
The mass spectrum of the Higgs bosons for various
We also used and
constraint is potentially dangerous.
How about the Higgs contributions to the S,T-parameter
bounds yield the constraint to
TeV
for TeV
The sensitivity of is small. and
and it corresponds to
★
◎ The 4th generation quarks drastically increases
◎ An example for the scenario with
Inputs:
Outputs:
yukawa couplings
Decay width into WW, ZZ
Enhancement of Higgs production
◎ An example for the scenario with
Inputs:
Outputs:
yukawa couplings
Decay width into WW, ZZ
Enhancement of Higgs production
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 (2+1)-Higgs model.
In Progress:
Branching ratio of the Higgs
Decay mode of the Higgs bosons
etc.
Lepton sectorMajorana neutrinosetc.
Under construction:
Thank you,