MeV sterile neutrinos in low reheating temperature cosmological scenarios

TL;DR

This paper explores how low reheating temperatures in the early universe can suppress sterile neutrino abundance, weakening cosmological bounds and making them detectable in future experiments, especially for neutrinos over 1 MeV.

Contribution

It demonstrates that low reheating temperature scenarios significantly relax cosmological constraints on sterile neutrinos, opening new experimental possibilities.

Findings

Sterile neutrino abundance is suppressed at low reheating temperatures.

Cosmological bounds on sterile neutrinos are less restrictive in these scenarios.

Sterile neutrinos over 1 MeV could be detectable in future experiments.

Abstract

It is commonly assumed that the cosmological and astrophysical bounds on the mixings of sterile with active neutrinos are much more stringent than those obtained from laboratory measurements. We point out that in scenarios with a very low reheating temperature T_RH << 100 MeV at the end of (the last episode of) inflation or entropy creation, the abundance of sterile neutrinos becomes largely suppressed with respect to that obtained within the standard framework. Thus, in this case cosmological bounds become much less stringent than usually assumed, allowing sterile neutrinos to be ``visible'' in future experiments. Here, we concentrate on massive (mostly sterile) neutrinos heavier than 1 MeV.