Lepton flavor violation and scotogenic Majorana neutrino mass in a Stueckelberg $U(1)_X$ model

TL;DR

This paper develops a scotogenic Majorana neutrino mass model within a gauged U(1)_X extension, incorporating the Stueckelberg mechanism, and explores its implications for dark matter stability, lepton flavor violation, and experimental constraints.

Contribution

It introduces a novel U(1)_X extension with Stueckelberg mechanism for neutrino mass and dark matter, analyzing LFV processes and experimental sensitivities.

Findings

Lepton flavor violating processes are constrained by upcoming experiments.

Tau decays could be observed at Belle II with sufficient sensitivity.

Dark matter relic density and direct detection constraints are satisfied.

Abstract

We construct a scotogenic Majorana neutrino mass model in a gauged $U(1)_X$ extension of the standard model, where the mass of the gauge boson and the unbroken gauge symmetry, which leads to a stable dark matter (DM), can be achieved through the Stueckelberg mechanism. It is found that the simplest version of the extended model consists of the two inert-Higgs doublets and one vector-like singlet fermion. In addition to the Majorana neutrino mass, we study the lepton flavor violation (LFV) processes, such as $\ell_i \to \ell_j \gamma$, $\ell_i \to 3 \ell_j$, $\mu-e$ conversion rate in nucleus, and muonium-antimuonium oscillation. We show that the sensitivities of $\mu\to 3e$ and $\mu-e$ conversion rate designed in Mu3e and COMET/Mu2e experiments make both decays the most severe constraints on the $\mu\to e$ LFV processes. It is found that $\tau\to \mu \gamma$ and $\tau\to 3\mu$ can reach the designed significance level of Belle II. In addition to explaining the DM relic density, we also show that the DM-nucleon scattering cross section can satisfy the currently experimental limit of DM direct detection.