TeV scale U niversal seesaw, vacuum stability and Heavy Higgs at the LHC

1. TeV scale Universal seesaw, vacuum stability and Heavy Higgs at the LHC Yongchao Zhang (张永超) Center for High-Energy Physics, Peking University w/ Rabi N. Mohapatra, 1401.6701, JHEP06(2014)072 June 14, 2014 Shaanxi Normal University

2. Outline • Motivation • Modeling • Stabilizing the vacuum • Heavy Higgs • Heavy vector-like fermions • Neutrinos • Conclusion

3. 126 GeV Higgs observed!

4. PDG2013 1112.3022 SM vacuum unstable (metastable) • Running of λ is sensitive to the Higgs and top masses • What does near criticality of the H and t masses mean? Nearby new physics?...... • Maybe NP are needed to stabilize the SM vacuum, with new particles coupling to the SM Higgs

5. Main idea of the Left-Right universal Seesaw Model (SLRM) • Seesaw mechanism  SM quarks & charged leptons universal seesaw (Berezhiani 1983, Chang & Mohapatra 1987, Rajpoot 1987, Davidson & Wali 1987, Babu & Mohapatra 1989, 1990) • Left-right symmetric (Mohapatra & Pati, 1975, Senjanovic & Mohapatra, 1975) • Providing a solution to the Strong CP problem without an axion(Babu& Mohapatra, 1989, 1990)

6. matter content • Left-right symmetric • Adding the vector-like fermions to realize the seesaw mechanism

7. Simple Higgs sector • Only two Higgs doublets • Simple potential • LR symmetry: softly broken by the mass terms, • LR symmetry: only one extra scalar coupling, • Simple spectrum: only two (neutral) physical Higgs particles

8. Yukawa interaction • LR symmetric Yukawa interaction • Seesaw mechanism • O(1) Yukawa interactions: ultra-heavy partner fermions;TeV RH scale and partner masses: smaller couplings. • All the flavor structure resides in the Yukawa interactions, e.g., with MP,N,E & Yu diagonal,

9. Stabilizing the vacuum • The scalar quartic coupling is larger than in the SM, • Top Yukawa coupling generally larger than in the SM (the NLO corrections beyond seesaw is important), • The other couplings are generally negligible, altough they are larger than in the SM,

10. RGEs • RGEs below the RH scale

11. RGEs • RGEs above the RH scale

12. Matching conditions • Gauge couplings in the context of GUT (Mohapatra, 2002, book), • Scalar quartic couplings • Yukawa couplings

13. Vacuum stability • Vacuum stability conditions • Gauge interactions grand unified: RGE run only up to the GUT scale but not to the Planck scale • Perturbativity: λ1 < 3 • Simplifying the heavy mass parameters,Given vR & MF, all the Yukawa couplings are fixed • Free parameters in the simplified case vR λ1 MF

14. Vacuum stability: examples

15. Vacuum stability: parameter scan ATLAS-CONF-2013-051 Collider constraint

16. Vacuum stability: if λ2<0… ATLAS-CONF-2013-051 Collider constraint Collider constraint

17. Constraints on heavy Higgs (H) mass • Heavy Higgs mass is determined by the RH scale and λ1 • The matching condition of λ1 says that λ1 > λ, • The parameter scan shows that when λ1 is large enough it would enter the non-perturbative region at high energy scales, NOT consider constraint on the heavy vector-like fermions

18. Constraints on the fermion masses • Large Yukawa couplings would worsen the stability problem. • One important implication is that the partners of bottom and tauon is below the RH scale. • The large top Yukawa coupling contribute significantly to the top partner mass. Upper bounds

19. SM Higgs in the extended model • Higgs Production: The top partner loop is suppressed by the scalar mixing or the LH fermion top mixing angle,The top quark loop dominates… • Higgs decayBelow the RH scale, all the beyond SM particles are integrated out, and we recover the SM as an effective theory

20. Heavy Higgs production at LHC14 • Top loop gluon fusion channel is suppressed by the scalar mixing or LH top mixing angle, • Dominate channel: gluon fusion via top partner loop

21. Heavy Higgs decay • Dominate decay channels • Theses 2nd-4th channels are suppressed, respectively, by • The diphoton channel is dominated by the WR, t and T loops,generally of order 10-5, not practically observable

22. Quartering rule in the massive limit • In the massive limit vR→, the fermion channel is suppressed by the LR scale ratio, and the other three channels, • This originate from the coupling of H to the four component of χL in the potential.

23. Quartering rule in the massive limit

24. What if MH>2MF?... • In a large parameter space, the di-top-partner channel is not allowed • The bottom and tau partner channels are suppressed by the small scalar mixing and light-heavy fermion mixing anglesgenerally of order 10-3

25. Neutrinos in SLRM without • Dirac neutrino masses generated at 2-loop level (Babu & X-G He, 1989)

26. Neutrinos in SLRM with • With only Dirac masses for the neutrino partners:Ultrahigh energy scale of MN or ultra-small Yukawa couplings • With both Dirac and Majorana masses of MN, in the basis of • The neutrino masses read, when MN≤ ML,R

27. Conclusion • Vacuum stabilized in the left-right universal seesaw model • Simple Higgs sector: only one heavy neutral Higgs H, • Higgs H mass is constrained below the RH scale, • The phenomenology of H could be tested at LHC14, with the characteristic quartering decay rule, • The vector-like heavy fermions are at or below the RH scale, and are accessible at LHC.

28. Open questions • Neutrino physics in SLRM? • SLRM  Higgs inflation? • CP violation and baryogenesis in SLRM?

29. Thank you very much!!!

30. Backup slides

31. Strong CP problem • Strong CP parameter • With parity soft broken, θ=0, • Then the strong CP violation can be generated at 2-loop level (Babu & Mohapatra, 1990)

32. Vacuum stability: parameter scan

33. Vacuum stability: parameter scan

34. Collider constraint on MF ATLAS-CONF-2013-051

35. SM Higgs coupling • Triple Higgs coupling

36. Couplings in H decay • Couplings beyond SM in the H decay widthsWith ε and α, respectively, the scalar mixing angle and Light-Heavy fermion mixing angle