Lepton flavor violating Higgs boson decays are studied within the context of seesaw models with Majorana massive neutrinos. Two models are considered: The SM-seesaw, with the Standard Model Particle content plus three right handed neutrinos, and the MSSM-seesaw, with the Minimal Supersymmetric Standard Model particle content plus three right handed neutrinos and their supersymmetric partners. The widths for these decays are derived from a full one-loop diagrammatic computation in both models, and they are analyzed numerically in terms of the seesaw parameters, namely, the Dirac and Majorana mass matrices. Several possible scenarios for these mass matrices that are compatible with neutrino data are considered. In the SM-seesaw case, very small branching ratios are found for all studied scenarios. These ratios are explained as a consequence of the decoupling behaviour of the heavy right handed neutrinos. In contrast, in the MSSM-seesaw case, sizeable branching ratios are found for some of the leptonic flavor violating decays of the MSSM neutral Higgs bosons and for some choices of the seesaw matrices and MSSM parameters. The relevance of the two competing sources of lepton flavor changing interactions in the MSSM-seesaw case is also discussed. The non-decoupling behaviour of the supersymmetric particles contributing in the loop-diagrams is finally shown.Comment: 44pgs. Version to appear in Phys.Rev.

We revisit the one-loop calculation of the annihilation of a pair of the lightest neutralinos into a pair of photons, a pair of gluons and also a Z photon final state. For the latter we have identified a new contribution that may not always be negligible. For all three processes we have conducted a tuned comparison with previous calculations for some characteristic scenarios. The approach to the very heavy Higgsino and W-ino is studied and we argue how the full one-loop calculation should be matched into a more complete treatment that was presented recently for these extreme regimes. We also give a short description of the code that we exploited for the automatic calculation of one-loop cross sections in the minimal supersymmetric model that could apply, both for observables at the colliders and for astrophysics or relic density calculations. In particular, the automatic treatment of zero Gram determinants which appear in the latter applications is outlined. We also point out how generalized nonlinear gauge-fixing constraints can be exploited.

We analyze the supersymmetric ͑SUSY͒ QCD contribution to the h 0 bb coupling at one loop in the minimal supersymmetric standard model in the decoupling limit. Analytic expressions in the large SUSY mass region are derived and the decoupling behavior of the corrections is examined in various limiting cases, where some or all of the SUSY mass parameters become large. We show that in the decoupling limit of large SUSY mass parameters and large CP-odd Higgs boson mass, the h 0 bb coupling approaches its standard model value at one loop. However, the onset of decoupling is delayed when tan ␤ is large. In addition, the one-loop SUSY-QCD corrections decouple if the masses of either the bottom squarks or the gluino are separately taken large; although the approach to decoupling is significantly slower in the latter case.

The MSSM with large tan β and heavy squarks (Mq > ∼ 1 TeV) is a theoretically well motivated and phenomenologically interesting extension of the SM. This scenario naturally satisfies all the electroweak precision constraints and, in the case of not too heavy slepton sector (Ml < ∼ 0.5 TeV), can also easily accommodate the (g − 2) µ anomaly. Within this framework non-standard effects could possibly be detected in the near future in a few lowenergy flavour-violating observables, such as B(B → τ ν), B(B s,d → ℓ + ℓ − ), B(B → X s γ), and B(µ → eγ). Interpreting the (g − 2) µ anomaly as the first hint of this scenario, we analyse the correlations of these low-energy observables under the additional assumption that the relic density of a Bino-like LSP accommodates the observed dark matter distribution.

The one-loop contributions to the branching ratios for leptonic τ decays are calculated in the CP conserving 2HDM(II). We found that these one-loop contributions, involving both neutral and charged Higgs bosons, dominate over the tree-level H ± exchange, the latter one being totally negligible for the decay into e. The analysis is focused on large tan β enhanced contributions to the considered branching ratios. We derive a simple analytical expression for the one-loop contribution which holds in this case. We show that the leptonic branching ratios of τ are complementary to the Higgsstrahlung processes for h(H) and have a large potential on constraining parameters of the model. In this work we provide upper limits on Yukawa couplings for both light h and light A scenarios and we derive new lower limit on mass of M H ± as a function of tan β, which differs significantly from what was considered as standard constraint based on the tree-level H ± exchange only. Interestingly we obtain also an upper limit on M H ± . For a SMlike h scenario, with heavy and degenerate additional Higgs bosons, one-loop corrections disappear.