Bounds on very low reheating scenarios after Planck

Abstract

We consider the case of very low reheating scenarios [${T}_{\mathrm{RH}}\ensuremath{\sim}\mathcal{O}(\mathrm{MeV})$] with a better calculation of the production of the relic neutrino background (with three-flavor oscillations). At 95% confidence level, a lower bound on the reheating temperature ${T}_{\mathrm{RH}}>4.1\text{ }\text{ }\mathrm{MeV}$ is obtained from big bang nucleosynthesis, while ${T}_{\mathrm{RH}}>4.7\text{ }\text{ }\mathrm{MeV}$ from Planck data (allowing neutrino masses to vary), the most stringent bound on the reheating temperature to date. Neutrino masses as large as 1 eV are possible for very low reheating temperatures.