This work explores the impact of an early matter-dominated (EMD) era on dark matter (DM) genesis within the paradigms of weakly interacting massive particles (WIMPs) and feebly interacting massive particles (FIMPs). The study reexamines how an EMD era, which significantly alters the Hubble expansion rate and injects entropy, can modify DM formation. Using the scalar singlet DM model as a case study, it is shown that a continuous transition between the WIMP and FIMP scenarios is possible, broadening the parameter space.

This presentation examines the effects of an early matter-dominated (EMD) era on dark matter genesis, particularly focusing on the modification of the Hubble expansion rate and entropy injection. By analyzing the scalar singlet model, it is demonstrated that the EMD era facilitates a continuous transition between weakly interacting massive particles (WIMPs) and feebly interacting massive particles (FIMPs). This work significantly broadens the viable parameter space for dark matter models.