Cosmology of Sub-MeV Dark Matter Freeze-In

Dark matter (DM) could be a relic of freeze-in through a light mediator, where the DM is produced by extremely feeble, IR-dominated processes in the thermal standard model plasma. In the simplest viable models with DM lighter than 1 MeV, the DM has a small effective electric charge and is born with a nonthermal phase-space distribution. This DM candidate would cause observable departures from standard cosmological evolution. In this work, we combine data from the cosmic microwave background (CMB), Lyman-alpha forest, quasar lensing, stellar streams, and Milky Way satellite abundances to set limits on freezein DM masses up to similar to 20 keV, with the exact constraint depending on whether the DM thennalizes in its own sector. We perform forecasts for the CMB-S4 experiment, the Hydrogen Epoch of Reionization Array, and the Vera Rubin Observatory, finding that freeze-in DM masses up to similar to 80 keV can be explored.

Automated summary

Research suggests that dark matter may be a relic of freeze-in through a light mediator. The study combines data from various sources to set limits on freeze-in dark matter masses and makes forecasts for future experiments to explore freeze-in dark matter masses.