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, , JHEP06(2014)072 June 14, 2014 Shaanxi Normal University

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

126 GeV Higgs observed! 3

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 PDG

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) 5

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

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 7

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 M P,N,E & Y u diagonal, 8

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, 9

RGEs RGEs below the RH scale 10

RGEs RGEs above the RH scale 11

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

Vacuum stability Vacuum stability conditions Gauge interactions grand unified: RGE run only up to the GUT scale but not to the Planck scale Perturbativity: λ 1 < 3 Simplifying the heavy mass parameters, Given v R & M F, all the Yukawa couplings are fixed Free parameters in the simplified case λ1λ1 vRvR MFMF 13

Vacuum stability: examples 14

Vacuum stability: parameter scan Collider constraint 15 ATLAS-CONF

Vacuum stability: if λ 2 <0… Collider constraint Collider constraint 16 ATLAS-CONF

Constraints on heavy Higgs (H) mass Heavy Higgs mass is determined by the RH scale and λ 1 The matching condition of λ 1 says that λ 1 > 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 17

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 18

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 decay Below the RH scale, all the beyond SM particles are integrated out, and we recover the SM as an effective theory 19

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 20

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

Quartering rule in the massive limit 22

Quartering rule in the massive limit 23

What if M H >2M F ?... 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 angles generally of order

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

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

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. 27

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

Thank you very much!!!

Backup slides

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) 31

Vacuum stability: parameter scan 32

Vacuum stability: parameter scan 33

Collider constraint on M F ATLAS-CONF

SM Higgs coupling Triple Higgs coupling 35

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