Seasons of dark matter freeze-in shaped by the weather of the early Universe

Quantifying the imprints of freeze-in dark matter (DM) on cosmological structures requires knowledge of its phase-space distribution. We investigate how variations in the cosmological history before nucleosynthesis, the"weather"of that epoch, give rise to distinct"seasons"in the DM momentum distribution that govern its warmness. Studying decay-driven production across diverse cosmological histories, we map how these conditions shape DM phase-space properties. Our study quantifies how the early universe composition plays a key role in determining the mass bound on freeze-in DM.