Search

We present the first complete calculation of flavour violating lepton decays taking into account all supersymmetric (SUSY) and non-SUSY contributions in the context of the supersymmetric inverse seesaw, a specific SUSY low-scale seesaw model. We consider radiative and 3-body lepton decays as well as neutrinoless μ−econversion in muonic atoms and perform a full one-loop calculation in the mass basis. Taking CMSSM-like boundary conditions for the soft SUSY breaking parameters, we find that cancellations between different contributions are present in several regions, which might reduce the branching ratios by as much as one order of magnitude. This has important consequences when translating current measurements into constraints and estimating the reach of future experiments, and justifies the use of a full calculation. We also show that the ratio of different cross-sections can discriminate between dominant SUSY or non-SUSY contributions.

In the inverse seesaw model (ISS), the smallness of the neutrino masses is related to the smallness of a lepton number violating mass term whilst the seesaw scale is naturally close to the TeV scale, which allows for large effects in lepton flavor and universality violating observables. With the ongoing and planned measurements of the Higgs boson properties at the LHC, we found timely to investigate the possibility of having large lepton flavor violating Higgs decay (LFVHD) rates within the context of the ISS, considering the most generic case where three additional pairs of massive right-handed singlet neutrinos are added to the Standard Model particle content. We present a full one-loop computation of the LFVHD rates and analyze in full detail the predictions as functions of the various relevant ISS parameters, which are required to be compatible with the present neutrino data and the present experimental bounds for the three LFV radiative decays, and also consistent with other constraints, like perturbativity of the neutrino Yukawa couplings. At the end, we conclude on the maximum allowed LFVHD rates within the ISS, which may reach maximal values of order 10−5for the H→eτ‾and H→μτ‾channels, close to the expected future LHC sensitivities.

In this paper we consider a Higgs boson with mass and other properties compatible with those of the recently discovered Higgs particle at the LHC, and explore the possibility of new Higgs leptonic decays, beyond the standard model, with the singular feature of being lepton flavor violating (LFV). We study these LFV Higgs decays, H → lklm, within the context of the inverse seesaw model (ISS) and consider the most generic case where three additional pairs of massive right-handed singlet neutrinos are added to the standard model particle content. We require in addition that the input parameters of this ISS model are compatible with the present neutrino data and other constraints, like perturbativity of the neutrino Yukawa couplings. We present a full one-loop computation of the BR(H → lklm) rates for the three possible channels, lklm = μτ, eτ, eμ, and analyze in full detail the predictions as functions of the various relevant ISS parameters. We study in parallel the correlated one-loop predictions for the radiative decays, lm → lkγ, within this same ISS context, and require full compatibility of our predictions with the present experimental bounds for the three radiative decays, μ → eγ, τ → μγ, and τ → eγ. After exploring the ISS parameter space we conclude on the maximum allowed LFV Higgs decay rates within the ISS. [ABSTRACT FROM AUTHOR]

The article presents a study on the decoupling behavior of heavy sneutrinos in supersymmetric low-scale seesaw models. The study examines the claims about the large contributions of right-handed sneutrinos to the observables of lepton flavor violation (LFV) and evaluates the Z-penguin diagrams to assess such contributions. The study finds that the Z-penguin contributions of heavy sneutrinos dominate their photonic contributions.

We discuss weak kaon decays in a scenario in which the Standard Model is extended by massive sterile fermions. After revisiting the analytical expressions for leptonic and semileptonic decays we derive the expressions for decay rates with two neutrinos in the final state. By using a simple effective model with only one sterile neutrino, compatible with all current experimental bounds and general theoretical constraints, we conduct a thorough numerical analysis which reveals that the impact of the presence of massive sterile neutrinos on kaon weak decays is very small, less than 1% on decay rates. The only exception is B(KL→νν), which can go up to O(10-10), thus possibly within the reach of the KOTO, NA62 and SHIP experiments. Plans have also been proposed to search for this decay at the NA64 experiment. In other words, if all the future measurements of weak kaon decays turn out to be compatible with the Standard Model predictions, this will not rule out the existence of massive light sterile neutrinos with non-negligible active-sterile mixing. Instead, for a sterile neutrino of mass below mK, one might obtain a huge enhancement of B(KL→νν), otherwise negligibly small in the Standard Model. [ABSTRACT FROM AUTHOR]