Detectable and Defect-Free Dark Photon Dark Matter

Ultralight dark photons are compelling dark matter candidates, but their allowed kinetic mixing with the standard model photon is severely constrained by requiring that the dark photons do not collapse into a cosmic string network in the early Universe. Direct detection in minimal production scenarios for dark photon dark matter is strongly limited, if not entirely excluded; discovery of sub-meV dark photon dark matter would therefore point to a nonminimal dark sector. We describe a model that evades such constraints, capable of producing cold dark photons in any parameter space accessible to future direct detection experiments. The associated production dynamics yield additional signatures in cosmology and small-scale structure, allowing for possible positive identification of this particular class of production mechanisms. Published by the American Physical Society 2025