Current constraints on cosmological scenarios with very low reheating temperatures

Abstract: We present an updated analysis of cosmological models with very low reheating scenarios ($T_\text{RH} \sim \mathcal{O}(\text{MeV})$). Our study includes a more precise computation of neutrino distribution functions, leveraging the latest datasets from cosmological surveys. We perform a joint analysis that combines constraints from Big Bang Nucleosynthesis, the Cosmic Microwave Background, and galaxy surveys, alongside separate investigations of these datasets, carefully assessing the impact of different choices of priors. At the $95\%$ confidence level, we establish a lower bound on the reheating temperature of $T_\text{RH} > 5.96 \; \text{MeV} $, representing the most stringent constraint to date.