Structure formation limits on axion-like dark matter

Abstract We derive structure formation limits on dark matter (DM) composed of keV-scale axion-like particles (ALPs), produced via freeze-in through the interactions with photons and Standard Model (SM) fermions. employ Lyman-alpha (Ly-α) forest data sets as well observed number Milky Way (MW) subhalos. compare results obtained using Maxwell-Boltzmann quantum statistics for describing SM bath. It should be emphasized that presence logarithmic divergences complicates calculation production rate, which can not parameterized a simple power law behaviour. The results, in combination X-ray bounds, exclude possibility photophilic “frozen-in” ALP DM mass below ∼ 19. For photophobic scenario, couples primarily to fermions, distribution function is peaked at somewhat lower momentum hence such realization we find weaker mass. Future facilities, upcoming Vera C. Rubin observatory, will provide measurements current bounds significantly improved 80.