Thermal Dark Photon Dark Matter, Coscattering, and Long-lived ALPs

Abstract: We study the thermal freeze-out of a dark photon dark matter in the so-called dark-axion portal - a triple coupling among a dark photon, an axion-like particle and the SM $\gamma$ or $Z$ boson. We analyze in detail the thermal production regimes: coscattering (aka conversion driven freeze-out), mediator freeze-out, and coannihilations. We found viable DM scenarios fulfilling the correct relic abundance in the three regimes. Apart of analyzing the parameter space for dark state masses between the GeV-TeV scale, we explore the prospects of having the axion-like field as a long-lived particle, possibly to be observed at the LHC and future detectors.