Electron and muon $g-2$, radiative neutrino mass, and $\ell' \to \ell \gamma$ in a $U(1)_{e-\mu}$ model

Abstract

A nonconventional $U(1)_{e-\mu}$ gauge model is proposed to explain the unexpected anomalous magnetic moments of the electron and muon (lepton $g-2$), where only the right-handed electron and muon in the standard model carry the $U(1)_{e-\mu}$ 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 singlet, 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 $\ell' \to \ell \gamma$ and lepton $g-2$, where the lepton $g-2$ is proportional to $m_{\ell}$. 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 $m_e$ and $m_\mu$ 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 $\mu\to e \gamma$ decay is suppressed, the resulting branching ratio for $\tau\to e \gamma$ can be of $O(10^{-8})$, and that for $\tau\to \mu \gamma$ can be as large as the current upper limit.