Light Gauge Boson Z’ And LFV Decays Of The Electroweak Gauge Boson Z

Although the standard model(SM),which contains electroweak theory and quantum chro-modynamics(QCD),can successfully describe the fundamental interactions among elementary particles,many problems,for example,naturalness and the existence of the gauge hierarchy problems,indicate that the SM should be embedded in a more fundamentall theory.So the S-M is generally regarded as an effective realization of an underlying theory to be yet discov-ered.Therefore,a lot of new physical theories beyond the SM(BSM)have been proposed in order to solve these problems.Among a lot of new physical theories beyond the SM,An extra neutral,massive,color singlet gauge boson,usually called Z’,is a common feature of BSM scenarios,which arises from general extensions of the SM gauge groups.That is to say,Almost all new physical models containing the new U(1)gauge group predicted the new gaueg boson Z’.For example,331 model,LR model,Lμ-Lτ model etc.The ATLAS and CMS cooperative group conducted a large number of experiments on Z and gave a lower quality limit.Z’ boson is of great significance for the search of new physics.If we can detect the existence of Z’ boson in future collider experiments,we will provide experimental evidence for the existence of new physics.Because of the recent hint for some lepton flavor anomaly,for example:the muon anoma-lous magnetic moment aμ puzzle,the NuTeV anomaly and the recent hint for the lepton flavor violating(LFV)Higgs decay H→μτ.Therefore,there is a growing interest of a light,LFV gauge boson Z’,which is assumed to be leptophilic and only coupling to the second and third generation leptons.This class of gauge boson Z’ can trivially satisfy the existing experimen-tal constraints involving first generation leptons,and all of quarks.Reference has shown that it might explain the aμ anomaly in the case of satisfying the constraints from tau decays and relevant LHC data.In this letter,we will consider the constraints on the Z’ couplings from the flavor conserving(FC)leptonic decay Z→ll of the electroweak gauge boson Z and further calculate its contributions to the LFV decay Z → τμ.Our numerical results show that,in the case of satisfying the relevant constraints,the light gauge boson Z’ can make the LFV decay process Z → τμ be proved at future e+e-colliders.Certainly the light gauge boson Z’ can also induce the LFV decay H → τμ via the LFC and LFV couplings Z’ττ(Z’μμ)and Z’τμat one-loop level.However,considering the constraints on the Z’ couplings,we find that the branching ratio BR(H → τμ)is smaller than 10-9,which is consistent with the results given.