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Register a new userVacuum Stability and Higgs Diphoton Decays in the MSSM
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Current Higgs data at the Large Hadron Collider is compatible with a SM signal at the 2$sigma$ level, but the central value of the signal strength in the diphoton channel is enhanced with respect to the SM expectation. If the enhancement resides in the diphoton partial decay width, the data could be accommodated in the Minimally Supersymmetric Standard Model (MSSM) with highly mixed light staus. We revisit the issue of vacuum instability induced by large mixing in the stau sector, including effects of a radiatively-corrected tau Yukawa coupling. Further, we emphasize the importance of taking into account the $tanbeta$ dependence in the stability bound. While the metastability of the Universe constrains the possible enhancement in the Higgs to diphoton decay width in the light stau scenario, an increase of the order of 50% can be achieved in the region of large $tanbeta$. Larger enhancements may be obtained, but would require values of $tanbeta$ associated with non-perturbative values of the tau Yukawa coupling at scales below the GUT scale, thereby implying the presence of new physics beyond the MSSM.
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The search for the production of weakly-interacting SUSY particles at the LHC is crucial for testing supersymmetry in relation to dark matter. Decays of neutralinos into Higgs bosons occur over some significant part of the SUSY parameter space and represent the most important source of $h$ boson production in SUSY decay chains in the MSSM. We study h production in neutralino decays using scans of the phenomenological MSSM. Whilst in constrained MSSM scenarios the decay chi^0_2 -> h chi^0_1 is the dominant channel, this does not hold in more general MSSM scenarios. On the other hand, the chi^0_2,3 -> h chi^0_1 decays remain important and are highly complementary to multi-lepton final states in the LHC searches. The perspectives for the LHC analyses at 8 and 14 TeV as well as the reach of an e+e- collider at 0.5, 1, 1.5 and 3 TeV are discussed.
The analysis of the Higgs search results at LEP showed that a part of the MSSM parameter space with non-zero complex phases could not be excluded, where the lightest neutral Higgs boson, h_1, has a mass of only about 45 GeV and the second lightest neutral Higgs boson, h_2, has a sizable branching fraction into a pair of h_1 states. Full one-loop results for the Higgs cascade decay h_2 --> h_1 h_1 are presented and combined with two-loop Higgs propagator corrections taken from the program FeynHiggs. Using the improved theoretical prediction to analyse the limits on topological cross sections obtained at LEP, the existence of an unexcluded region at low Higgs mass is confirmed. The effect of the genuine vertex corrections on the size and shape of this region is discussed.
In the MSSM with complex parameters loop corrections to the decays $H^+ to t bar{b}$ and $H^- to bar{t} b$ with $t to b W$ and $W to l u$ lead to CP-violating asymmetries: a decay rate asymmetry, a forward-backward asymmetry and an energy asymmetry. We derive explicit formulas for them and perform a detailed numerical analysis. We study the dependence on the parameters and the phases involved. In particular, the influence of the running Yukawa coupling is taken into account. The decay rate asymmetry can go up to 25%, the forward-backward and the energy asymmetry up to 10%.
Precision measurements of the Higgs boson properties at the LHC provide relevant constraints on possible weak-scale extensions of the Standard Model (SM). In the context of the Minimal Supersymmetric Standard Model (MSSM) these constraints seem to suggest that all the additional, non-SM-like Higgs bosons should be heavy, with masses larger than about 400 GeV. This article shows that such results do not hold when the theory approaches the conditions for alignment independent of decoupling, where the lightest CP-even Higgs boson has SM-like tree-level couplings to fermions and gauge bosons, independently of the non-standard Higgs boson masses. The combination of current bounds from direct Higgs boson searches at the LHC, along with the alignment conditions, have a significant impact on the allowed MSSM parameter space yielding light additional Higgs bosons. In particular, after ensuring the correct mass for the lightest CP-even Higgs boson, we find that precision measurements and direct searches are complementary, and may soon be able to probe the region of non-SM-like Higgs boson with masses below the top quark pair mass threshold of 350 GeV and low to moderate values of $tanbeta$.
We consider the introduction of a complex scalar field carrying a global lepton number charge to the Standard Model and the Higgs inflation framework. The conditions are investigated under which this model can simultaneously ensure Higgs vacuum stability up to the Planck scale, successful inflation, non-thermal Leptogenesis via the pendulum mechanism, and light neutrino masses. These can be simultaneously achieved when the scalar lepton is minimally coupled to gravity, that is, when standard Higgs inflation and reheating proceed without the interference of the additional scalar degrees of freedom. If the scalar lepton also has a non-minimal coupling to gravity, a multi-field inflation scenario is induced, with interesting interplay between the successful inflation constraints and those from vacuum stability and Leptogenesis. The parameter region that can simultaneously achieve the above goals is explored.
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