Abstract:

I will discuss about a flavor-changing neutral current (FCNC) decay of the top quark induced by a new massive gauge boson Z', namely t --> c Z', based on a model of the gauged L_mu - L_tau symmetry (the difference between the muon and tauon numbers). This Z' boson is phenomenologically well-motivated: (i) it can explain the anomalous data observed by LHCb in b --> s mu^+ mu^- transitions if heavy (m_Z' >> m_b); (ii) it can solve the muon g-2 anomaly if light (m_Z' < 400 MeV). For these two cases, I will illustrate whether the decay rate of t --> c Z' succeeded by Z' --> mu^+ mu^- can be as large as an observable level at the LHC by taking into account B and K meson FCNC data. I will also discuss about the possibility that the decay K_L --> pi^0 Z' with Z' --> nu nubar may lead to apparent violation of the usual Grossman-Nir bound of B(K_L --> pi^0 nu nubar) < 1.4 x 10^-9.