Higgs mediated lepton flavor violating tau decays $tau to mu gamma$ and $tau to mu gamma gamma$ 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 $Htau mu$ is studied in the frame of effective field theories. The best constraint on the $Htau mu$ vertex, derived from the know measurement on the muon anomalous magnetic moment, is used to impose the upper bounds $Br(tau to mu gamma)<2.5times 10^{-10}$ and $Br(tau to mu gamma gamma)<2.3times 10^{-12}$, which are more stringent than current experimental limits on this class of transitions.

Double Flavor Violating Top Quark Decays in Effective Theories

The possibility of detecting double flavor violating top quark transitions $t to u_itau mu$ ($u_i=u,c$) is explored in a model--independent manner, using the effective Lagrangian approach. Low--energy data, on high precision measurements, and current experimental limits are used to constraint the $tu_iH$ and $Htau mu$ vertices and then to calculate the branching ratio BR$(t to u_itau mu)$. If in the Standard Model BR$(t to u_itau mu)$ is of the order of $10^{-13}$$-10^{-14}$, higgs--mediated double flavor violating top quark decays can occur with branching ratios ranging from $10^{-3}$ to $10^{-4}$ for 114.4 GeV$/c^2$ $< m_H<$ $2m_W$, that is at the reach of the CERN Large Hadron Collider.