We propose simple scenarios where lepton flavor-violating couplings generate the observed dark matter abundance through freeze-in of an axion-like particle with mass in the few keV range. Compared to flavor-diagonal freeze-in, this mechanism enhances dark matter stability, softens stellar cooling constraints and improves the experimental sensitivity of accelerator-based searches. These scenarios can be tested by future X-ray telescopes, and in some cases will be almost entirely probed by new searches for lepton flavor violation at high-intensity experiments such as Mu3e and MEG II.
@article{arxiv.2209.03371,
title = {Axion Dark Matter from Lepton flavor-violating Decays},
author = {Paolo Panci and Diego Redigolo and Thomas Schwetz and Robert Ziegler},
journal= {arXiv preprint arXiv:2209.03371},
year = {2023}
}