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.

Decays Z --> ggg and Z-prime --> ggg in the minimal 331 model

We perform a complete calculation at the one-loop level for the Zggg and Zggg couplings in the context of the minimal 331 model, which predicts the existence of a new Z gauge boson and new exotic quarks. Bose symmetry is exploited to write a compact and manifest SU_C(3)-invariant vertex function for the Vggg (V=Z,Z) coupling. Previous results on the $Zto ggg$ decay in the standard model are reproduced. It is found that this decay is insensitive to the effects of the new exotic quarks. This in contrast with the $Zto ggg$ decay, which is sensitive to both the standard model and exotic quarks, whose branching ratio is larger than that of the $Zto ggg$ transition by about a factor of 4.