Axion dark matter from lepton flavor-violating decays
Paolo Panci (Dipartimento di Fisica E. Fermi, Università di Pisa, Pisa, Italy, INFN, Sezione di Pisa, Pisa, Italy); Diego Redigolo (INFN, Sezione di Firenze, Sesto Fiorentino, Italy); Thomas Schwetz (Institut für Astroteilchenphysik, Karlsruhe Institute of Technology, Karlsruhe, Germany); Robert Ziegler (Institut für Theoretische Teilchenphysik, Karlsruhe Institute of Technology, Karlsruhe, Germany)
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.