Study of the lepton flavor-violating $Ztotaumu$ decay

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.

Implications of $D^0-overline{D^0}$ on the rare top quark decays $tto ugamma$ and $tto ug$

The recently observed mass difference of the $D^0-overline{D^0}$ mixing is used to predict the branching ratios of the rare top quark decays $tto ugamma$ and $tto ug$ in a model independent way using the effective Lagrangian approach. It is found that $Br(tto ugamma)<4times 10^{-4}$ and $Br(tto ug)<2times 10^{-3}$, which still may be within reach of the LHC collider.

Effective Lagrangian description of Higgs mediated flavor violating electromagnetic transitions: implications on lepton flavor violation

Higgs mediated flavor violating electromagnetic interactions, induced at the one--loop level by a nondiagonal $Hf_if_j$ vertex, with $f_i$ and $f_j$ charged leptons or quarks, are studied within the context of a completely general effective Yukawa sector that comprises $SU_L(2)times U_Y(1)$--invariant operators of up to dimension--six. Exact formulae for the one--loop $gamma f_if_j$ and $gamma gamma f_if_j$ couplings are presented and their related processes used to study the phenomena of Higgs mediated lepton flavor violation. The experimental limit on the $mu to egamma$ decay is used to derive a bound on the branching ratio of the $mu to egamma gamma$ transition, which is 6 orders of magnitude stronger than the current experimental limit. Previous results on the $tau to mu gamma$ and $tau to mu gamma gamma$ decays are reproduced. The possibility of detecting signals of lepton flavor violation at $gamma gamma$ colliders is explored through the $gamma gamma to l_il_j$ reaction, putting special emphasis on the $tau mu$ final state. Using the bound imposed on the $Htau mu$ vertex by the current experimental data on the muon anomalous magnetic moment, it is found that about half a hundred events may be produced in the International Linear Collider.

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.