Higgs mediated lepton flavor violating tau decays τ→μγ\tau \to \mu \gamma and τ→μγγ\tau \to \mu \gamma \gamma in effective theories

The size of the branching ratios for the $\tau \to \mu \gamma$ and $\tau \to \mu \gamma \gamma$ decays induced by a lepton flavor violating Higgs interaction $H\tau \mu$ is studied in the frame of effective field theories. The best constraint on the $H\tau \mu$ vertex, derived from the know measurement on the muon anomalous magnetic moment, is used to impose the upper bounds $Br(\tau \to \mu \gamma)<2.5\times 10^{-10}$ and $Br(\tau \to \mu \gamma \gamma)<2.3\times 10^{-12}$, which are more stringent than current experimental limits on this class of transitions.Comment: 6 pages, 3 figure

Study of the lepton flavor-violating Z′→τμZ'\to\tau\mu decay

The lepton flavor violating $Z^{\prime}\to\tau\mu$ 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 $Z^\prime\mu\tau$ 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 $\mathrm{Re}(\Omega_{L\mu\tau}\Omega^\ast_{R\mu\tau})$ parameter is constrained and it is found that $\mathrm{Re}(\Omega_{L\mu\tau}\Omega^\ast_{R\mu\tau})\sim 10^{-2}$ for a $Z^\prime$ boson mass of 2 TeV. Alongside, we employed the experimental restrictions over the $\tau\to\mu\gamma$ and $\tau\to\mu\mu^+\mu^-$ 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 $|\Omega_{\mu\tau}|^2$, 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 $Z^\prime\to\tau\mu$ 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.Comment: Revised versio