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Register a new userTesting neutrino mass generation mechanisms from the lepton flavor violating decay of the Higgs boson
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We investigate how observations of the lepton flavor violating decay of the Higgs boson ($h to ellell^prime$) can narrow down models of neutrino mass generation mechanisms, which were systematically studied in Refs. [1,2] by focusing on the combination of new Yukawa coupling matrices with leptons. We find that a wide class of models for neutrino masses can be excluded if evidence for $h to ellell^prime$ is really obtained in the current or future collider experiments. In particular, simple models of Majorana neutrino masses cannot be compatible with the observation of $h to ellell^prime$. It is also found that some of the simple models to generate masses of Dirac neutrinos radiatively can be compatible with a significant rate of the $h to ellell^prime$ process.
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The lepton flavor violating decay of the Standard Model-like Higgs (LFVHD) is discussed in the framework of the radiative neutrino mass model built in cite{Kenji}. The branching ratio (BR) of the LFVHD are shown to reach $10^{-5}$ in the most interesting region of the parameter space shown in cite{Kenji}. The dominant contributions come from the singly charged Higgs mediations, namely the coupling of $h^pm_2$ with exotic neutrinos. Furthermore, if doubly charged Higgs is heavy enough to allow the mass of $h^pm_2$ around 1 TeV, the mentioned BR can reach $10^{-4}$. Besides, we have obtained that the large values of the Br$(hrightarrowmutau)$ leads to very small ones of the Br$(hrightarrow etau)$, much smaller than various sensitivity of current experiments.
We propose a new mechanism to explain neutrino masses with lepton number conservation, in which the Dirac neutrino masses are generated at the two-loop level involving a dark matter candidate. In this model, branching ratios of lepton flavor violating decays of the Higgs boson can be much larger than those of lepton flavor violating decays of charged leptons. If lepton flavor violating decays of the Higgs boson are observed at future collider experiments without detecting lepton flavor violating decays of charged leptons, most of the models previously proposed for tiny neutrino masses are excluded while our model can still survive. We show that the model can be viable under constraints from current data for neutrino experiments, searches for lepton flavor violating decays of charged leptons and dark matter experiments.
The lepton flavor violating $Z^{prime}totaumu$ decay is studied in the context of several extended models that predict the existence of the new gauge boson named $Z^prime$. A calculation of the strength of the lepton flavor violating $Z^primemutau$ coupling is presented by using the most general renormalizable Lagrangian that includes lepton flavor violation. We used the experimental value of the muon magnetic dipole moment to bound this coupling, from which the $mathrm{Re}(Omega_{Lmutau}Omega^ast_{Rmutau})$ parameter is constrained and it is found that $mathrm{Re}(Omega_{Lmutau}Omega^ast_{Rmutau})sim 10^{-2}$ for a $Z^prime$ boson mass of 2 TeV. Alongside, we employed the experimental restrictions over the $tautomugamma$ and $tautomumu^+mu^-$ processes in the context of several models that predict the existence of the $Z^prime$ gauge boson to bound the mentioned coupling. The most restrictive bounds come from the calculation of the three-body decay. For this case, it was found that the most restrictive result is provided by a vector-like coupling, denoted as $|Omega_{mutau}|^2$, for the $Z_chi$ case, finding around $10^{-2}$ for a $Z^prime$ boson mass of 2 TeV. We used this information to estimate the branching ratio for the $Z^primetotaumu$ decay. According to the analyzed models the least optimistic result is provided by the Sequential $Z$ model, which is of the order of $10^{-2}$ for a $Z^prime$ boson mass around 2 TeV.
Exotic Higgs decays are promising channels to discover new physics in the near future. We present a simple model with a new light scalar that couples to the Standard Model through a charged lepton-flavor violating interaction. This can yield exciting new signatures, such as $h to e^+ e^+ mu^-mu^-$, that currently have no dedicated searches at the Large Hadron Collider. We discuss this model in detail, assess sensitivity from flavor constraints, explore current constraints from existing multi-lepton searches, and construct a new search strategy to optimally target these exotic, lepton-flavor violating Higgs decays.
In this paper we examine thoroughly the Higgs boson to mu tau decay via processes involving R parity violating couplings. By means of full one-loop diagrammatic calculations, we found that even if known experimental constraints, particularly including the stringent sub-eV neutrino mass bounds, give strong restrictions on some of the R parity violating parameters, the branching ratio could still achieve notable value in the admissible parameter space. Hence, the flavor violating leptonic decay is of interest to future experiments. We present here key results of our analysis. Based on the analysis, we give some comments on h -> e mu and h -> e tau also.
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