Electron and muon g − 2, radiative neutrino mass, and ℓ′ → ℓγ in a U(1)e−μ model

Abstract

A nonconventional U(1)e−μ gauge model is proposed to explain the observed neutrino masses and the unexpected anomalous magnetic moments of the electron and muon (lepton g−2), where for suppressing the neutrino coupling to Z′ gauge boson, only the right-handed electron and muon in the standard model carry the U(1)e−μ charge. Although the light lepton masses are suppressed when the gauge symmetry is spontaneously broken, they can be generated through the Yukawa couplings to newly introduced particles, such as vector-like lepton doublets and singlets, and scalar singlets. It is found that the same Yukawa couplings combined with the new scalar couplings to the Higgs can induce the radiative lepton-flavor violation processes ℓ′→ℓγ and lepton g−2, where the lepton g−2 is proportional to mℓ. When Majorana fermions and a scalar singlet are further added into the model, the active neutrinos can obtain masses via the radiative seesaw mechanism. When the bounds from the me and mμ and the neutrino data are satisfied, we find that the electron g−2 can reach an order of −10−12, and the muon g−2 can be an order of 10−9. In addition, when the μ→eγ decay is suppressed, the resulting branching ratio for τ→eγ can be of O(10−8), and that for τ→μγ can be as large as the current upper limit.