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Fourth Generation and Dynamical Electroweak Symmetry Breaking

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.

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Fourth Generation and Dynamical Electroweak Symmetry Breaking

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  1. 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

  2. Introduction It is a fundamental problem whether or not there exists a new generation. Notice that concept of the SM allows more thanthree generations: Anomaly free QCD is asymptotic free. @ 1-loop The Kobayashi-Maskawa theory is NOT limited to 3 generations. (repetition of 1,2,3 generations ) No theoretical reason to reject the 4th generation Also, it is NOT excluded by the EW precision data…

  3. ◎ 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.

  4. contents Introduction Status of the 4th generation  M.H., 1001.4335. Super heavy quarks and multi-Higgs doublets M.H., Miransky, PRD80(2009)013004. M.H., Miransky, 0912.4453. Summary

  5. Constraints on the 4th family

  6. ◎ constraints on the masses Particle Data Group (PDG) 2009 For quarks, CDF, 0912.1057. CDF, 0810.3349. For leptons, (PDG 2009) (stable case)

  7. is allowed !! ◎ Number of light neutrinos ★ Z boson invisible width at LEP by invisible Z width (PDG2008) ◎ Is it proof of the 3 generation?  NO !

  8. Constraints from the oblique parameters

  9. Favorable mass spectrum: ◎ Constraints from the S and T parameters G.D.Kribs, T.Plehn, M.Spannowsky, T.M.P.Tait, PRD76(‘07)075016. ---------------- ---------------- LEP EWWG 68% and 95% C.L. constraints • Higgs potential quickly falls down and hence becomes unstable at the scale less than 1 TeV!!

  10. Theoretical cutoff ★ Very recently, I reanalyzed the (S,T) constraints. I also took into account the RGE’s: (M.H., 1001.4335) ・ 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 quarticcouplings (If the couplings are so large, they diverge at some scale. ) 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.

  11. Red Blue Violet Green (SM4) (M.H., 1001.4335) for We varied Dirac-type neutrnos are assumed. The 1-loop RGE’s are employed.

  12. (I took ) is allowed in a wide parameter space!! is also possible. The mass difference of the fermions Favorable mass spectrum is contained in the following region: (Both of them are unlikely.)

  13. The Higgs boson in the SM4 is likely to be heavy, say, ○ △ Comparison with the earlier work probably, (S,T) 68% CL limit Kribs, et al, PRD76(‘07)075016. light Higgs scenario, say, Our work (S,T) 95%CL limit + RGE’s Several decay channels are still allowed! etc. The strategies are different.  Not necessarily contradict each other

  14. LEP direct search 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

  15. 4th generation quarks evidence/exclusion at LHC with early data

  16. @Taiwan National University discovery or exclusion of b’ at LHC (my estimate) If no excess is observed, ★ If we get evidence of the 4th family quarks, it will bring “New Era of Strong Dynamics”.

  17. 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)

  18. 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

  19. 4th generation!? Why?

  20. 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. Prediction of the top mass in the 3 generation model Too Large!! (PDG2009) The minimal 3 gen. model does not work.

  21. 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.

  22. ◎The low energy effective theory@ EWSB scale Higgs potential @ 1/Nc leading approximation

  23. ◎ 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.

  24. and for various composite scale (Landau pole) of t’ and b’ Numerical Analysis We calculate the mass spectrum by using the BHL approach: RGE for the (2+1)-Higgs doublets + compositeness conditions

  25. 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 , so we can evade ◎ We took a large constraint.

  26. CP even Higgs -- 3 CP odd Higgs -- 2 charged Higgs -- 2+2 The physical Higgs bosons in the 3 Higgs doublet model are

  27. What is the signature?

  28. ◎ An example data for the scenario with Inputs: Outputs:

  29. yukawa couplings Decay width into WW, ZZ Enhancement of Higgs production of H1

  30. ・ 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!

  31. Summary and discussions • There exists an allowed parameter region for the 4th generation model. Probably, theLHC 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.

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

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