LFV Couplings Of Z’ Boson And The Rare Decays Of τ Lepton And Pseudoscalar Mesons

Although the standard model（SM）of particle physics can successfully describe the weak interaction,the electromagnetic interaction and the strong interaction,there are still many problems have not be solved,such as the hierarchy problem.New physics beyond the SM is put forward in order to solve the problems that SM can not solve.Additional U（1）′gauge symmetries is one of the best motivated extensions of the standard model.And almost all models which are based on the gauge symmetry group SU（3）C× SU（2）L× U（1）Y× U（1）′predict the extra gauge boson Z′,such as the E6 models,the left-right（LR）models,the ”alternative”left-right（ALR）models and the 331 models.The neutrinos in standard model are massless,but the neutrino oscillation experiment,proved the existence of the neutrino mass,which showed that the lepton flavor violating（LFV）processes may occur.LFV signal can be deemed an indication of new physics beyond the SM.And the the extra gauge boson Z′can induce the LFV couplings to the SM fermion.Considering the constraints of the LFV processes μ → 3e and τ → 3μ on the LFV couplings Z′?_i?_j,in the contexts of the E6 models,the left-right（LR）models,the ”alternative” left-right（ALR）models and the 331 models,we investigate the contributions of the extra gauge boson Z′to the decay rates of the processes ?i→ ?jν_?（?）,τ → μP and P → μe with P = π⁰,η and η′.Our numerical results show that the maximal values of the branching ratios for these processes are not dependent on the Z′mass MZ′ at leader order.The maximum values of Br（τ → μν_?（?））are larger than those for Br（μ → eν_?（?））at least four orders of magnitude,the extra gauge boson Z′_X predicted by the E6 models can make the maximum value of the branching ratio Br（τ → μν_?（?））reach 1.1 × 10^-7.All Z′models considered in this paper can produce significant contributions to the process τ → μP.Among these Z’ models,the contribution of Z’ predicted by the pure LR model to the LFV decay τ → μP is the maximum.However,its maximal value of the branching ratio τ → μP is still lower than the corresponding experimental upper limit at least by one order of magnitude.Considering the constraints of the experimental upper bound for the LFV process μ → 3e on the LFV couplings Z′?_i?_j,the contributions of the extra gauge boson Z’ to the LFV meson decays P → μe are very small.The value of the branching ratio Br（P → μe）is far below its corresponding experimental upper bound for all of the Z’ models considered in this paper.