Bounds on very low reheating scenarios after Planck

TL;DR

This paper refines bounds on very low reheating temperatures after the Big Bang using neutrino background calculations and Planck data, establishing the most stringent limits to date.

Contribution

It provides improved calculations of relic neutrino production and tighter bounds on reheating temperature from cosmological data.

Findings

Lower bound on reheating temperature: 4.1 MeV from BBN

Lower bound: 4.3 MeV from Planck for light neutrinos

Most stringent bound: 4.7 MeV allowing neutrino masses up to 1 eV

Abstract

We consider the case of very low reheating scenarios ($T_{\rm RH}\sim\mathcal{O}({\rm MeV})$) 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 $T_{\rm RH}>4.1$ MeV is obtained from Big Bang Nucleosynthesis, while $T_{\rm RH}>4.3$ MeV from Planck data for very light ($\sum m_i = 0.06$ eV) neutrinos. If neutrino masses are allowed to vary, Planck data yield $T_{\rm RH}>4.7$ MeV, the most stringent bound on the reheating temperature to date. Neutrino masses as large as 1 eV are possible for very low reheating temperatures.