Download Higgs doublet model

Fourth Generation and
Dynamical Electroweak
Symmetry Breaking
2010.02.20
@KEK
Michio
Hashimoto
(KEK)
M.H., Miransky, PRD80(2009)013004.
M.H., Miransky, 0912.4453.
M.H., 1001.4335.
Kairaku-en
Introduction
• It is a fundamental problem whether or not there exists a new generation.
• Notice that concept of the SM allows more than three generations:
Anomaly free
QCD is asymptotic free.
@ 1-loop
The Kobayashi-Maskawa theory is NOT limited to 3 generations.
No theoretical reason to reject the 4th generation
(repetition of 1,2,3 generations )
Also, it is NOT excluded by the EW precision data…
◎ If the 4th generation exists…
NEW PHYSICS which is well-defined and
familiar in some aspect
Elementary Higgs may not be needed any longer
 Dynamical Electroweak Symmetry Breaking
Free from the problem of naturalness!?
Landau pole of yukawa
The LHC can discover/exclude it at early stage.
contents
Introduction

Status of the 4th generation
M.H., 1001.4335.
Super heavy quarks and
multi-Higgs doublets
M.H., Miransky, PRD80(2009)013004.
Summary
M.H., Miransky, 0912.4453.
Constraints on the 4th family
◎ constraints on the masses
Particle Data Group (PDG) 2009
For quarks,
CDF, 0912.1057.
CDF, 0810.3349.
For leptons,
(PDG 2009)
(stable case)
◎ Number of light neutrinos
★ Z boson invisible width at LEP
by invisible Z width (PDG2008)
◎ Is it proof of the 3 generation?
 NO !
is allowed !!
Constraints from the oblique parameters
◎ Constraints from the S and T parameters
G.D.Kribs, T.Plehn, M.Spannowsky, T.M.P.Tait, PRD76(‘07)075016.
Favorable mass spectrum:
------------------------------LEP EWWG 68% and 95% C.L. constraints
 Higgs potential quickly falls down and hence becomes
unstable at the scale less than 1 TeV!!
★ Very recently, I reanalyzed the (S,T) constraints.
(M.H., 1001.4335)
I also took into account the RGE’s:
・ Instability bound for the Higgs potential
(If the Higgs mass is so small, the Higgs potential is unstable at some scale.)
・ Tree-level unitarity bounds
for the yukawa and Higgs quartic couplings
(If the couplings are so large, they diverge at some scale. )
Theoretical cutoff
The cutoff should not be so small.
Otherwise, such a model is unlikely
to be valid in the LHC physics…
In earlier works, people considered only S,T
or assumed
etc…
I have varied all masses of the fermions and Higgs boson,
and then obtained favorable mass spectra.
(SM4)
(M.H., 1001.4335)
for
We varied
Red
Blue
Violet
Green
Dirac-type neutrnos are assumed.
The 1-loop RGE’s are employed.
The mass difference of the fermions
Favorable mass spectrum is
contained in the following region:
(I took
)
is allowed in a wide parameter space!!
is also possible.
(Both of them are unlikely.)
Comparison with the earlier work
Kribs, et al, PRD76(‘07)075016.
probably, (S,T) 68% CL limit
light Higgs scenario, say,
Our work
(S,T) 95%CL limit + RGE’s
The Higgs boson in the SM4 is likely to be heavy, say,
Several decay channels are still allowed!
○
△
etc.
The strategies are different.  Not necessarily contradict each other
Heavy Higgs does not contradict the EW precision data
in the 4th generation model.
This means that a tension between the Higgs mass fit
in the SM3 and the LEP lower bound can be removed.
SM3
LEP direct search
4th generation quarks
evidence/exclusion at LHC with early data
discovery or exclusion of b’ at LHC
@Taiwan National University
(my estimate)
If no excess is observed,
★
If we get evidence of the 4th family quarks,
it will bring “New Era of Strong Dynamics”.
Dynamical Electroweak Symmetry Breaking
The 4th generation quarks can be closely connected with
the DEWSB through their condensations. Holdom, PRL57(‘86)2496.
The yukawa coupling
runs very quickly and
reaches the Landau pole
at most several tens TeV.
This is a signal for
the DEWSB!!
(TeV)
Superheavy quarks and multi-Higgs doublets
M.H., Miransky, PRD80(2009)013004; 0912.4453.
◎ The yukawa couplings have the Landau pole ～ O(few TeV).
It suggests compositeness, i.e.,
the Nambu-Jona-Lasinio description is applicable in low energy.
A nonperturbative model
○ The point is that the masses of t’, b’ and t are O(v=246GeV).
★ The t’ and b’ condensations can dynamically trigger the EWSB
and also the top may contribute somewhat.
Multiple composite Higgs doublet model
2,3,4,5 Higgs doublets
4th generation!? Why?
Prediction of the top mass in the 3 generation model
Too Large!!
(PDG2009)
The minimal 3 gen. model does not work.
◎
Top See-saw
Dobrescu and Hill, PRL81(‘98)2634.
◎ Top mode standard model with extra dimensions
MH, Tanabashi, Yamawaki, PRD64(‘01)056003.
 4th generation model
Holdom, PRL57(‘86)2496.
Three Higgs doublet model
M.H., Miransky, 0912.4453.
NJL-Model
low energy effective theory @ composite scale
We consider only t’, b’ and t.
Such a NJL-type model can be produced by a topcolor model, for example.
◎The low energy effective theory @ EWSB scale
Higgs potential @ 1/Nc leading approximation
◎ When we ignore the EW 1-loop effect,
the (2+1)-Higgs structure is safely kept.
The quartic term is then written as
Higgs quartic coupling --- 2 Higgs part + 1 Higgs part
(2+1)-Higgs doublet model
(The mass terms are general one.)
Cf)
is absent.
Numerical Analysis
We calculate the mass spectrum by using the BHL approach:
RGE for the (2+1)-Higgs doublets + compositeness conditions
and
for various
composite scale (Landau pole) of t’ and b’
The mass spectrum of the Higgs bosons for various
We also used
 (2+1) Higgs structure
◎ within 95% CL limit of the (S,T)-constraint
◎ We took a large
, so we can evade
constraint.
The physical Higgs bosons in the 3 Higgs doublet model are
CP even Higgs -- 3
CP odd Higgs -- 2
charged Higgs -- 2+2
What is the signature?
◎ An example data for the scenario with
Inputs:
Outputs:
yukawa couplings
Decay width into WW, ZZ
Enhancement of Higgs production of H1
・ resonances in ttbar channel
・ The heavier Higgs H2 resonance may exist
in the ZZ mode.
・ Also, in the t’t’bar channels, there may appear
scalar resonances.
・
・
・
Higgs Phenomenology is quite rich!
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 somewhat.
• The dynamical model with the 4th generation
naturally yields multi-Higgs doublets.
We analyzed the (2+1)-Higgs model.
In Progress:
Decay mode of the Higgs bosons
Branching ratio of the Higgs
etc.
Under construction:
Lepton sector
Majorana neutrinos
etc.
Thank you,