Lepton flavor violating Z′ explanation of the muon anomalous magnetic moment

Abstract We discuss a minimal solution to the long-standing ( g − 2 ) μ anomaly in a simple extension of the Standard Model with an extra Z ′ vector boson that has only flavor off-diagonal couplings to the second and third generation of leptons, i.e. μ , τ , ν μ , ν τ and their antiparticles. A simplified model realization, as well as various collider and low-energy constraints on this model, are discussed. We find that the ( g − 2 ) μ -favored region for a Z ′ lighter than the tau lepton is totally excluded, while a heavier Z ′ solution is still allowed. Some testable implications of this scenario in future experiments, such as lepton-flavor universality-violating tau decays at Belle 2, and a new four-lepton signature involving same-sign di-muons and di-taus at HL-LHC and FCC-ee, are pointed out. A characteristic resonant absorption feature in the high-energy neutrino spectrum might also be observed by neutrino telescopes like IceCube and KM3NeT.