Muon-induced baryon number violation

TL;DR

This paper investigates how light new physics can mimic and produce signals similar to muon-to-electron conversion, challenging the interpretation of experimental searches for charged-lepton flavor violation.

Contribution

It introduces a novel scenario where light dark sector interactions can produce signals that imitate muon-to-electron conversion, expanding the understanding of potential backgrounds in such experiments.

Findings

Light new physics can produce energetic electrons above the expected signal peak.

Muon-nucleon annihilation into a dark sector is a viable process producing detectable signals.

Constraints from nuclear stability and neutron star environments are relevant for these models.

Abstract

The search for charged-lepton flavor violation in muon capture on nuclei is a powerful probe of heavy new physics. A smoking gun signal for $\mu \rightarrow e$ conversion is a monochromatic electron with energy almost equal to the muon mass. We show that light new physics can mimic this signature and that it can also lead to electrons above the $\mu \rightarrow e$ signal peak. A concrete example of such light new physics is $\mu^- $-nucleon annihilation into a light dark sector, which can produce an energetic $e^-$ as well as $e^+e^-$ byproducts. Due to the size of the muon mass, the exotic muon capture process can be kinematically allowed, while the otherwise stringent constraints, e.g., from proton decay, are kinematically forbidden. We also discuss other relevant constraints, including those from the stability of nuclei and muon capture in the interior of neutron stars.