Boosted Neutrinos and Relativistic Dark Particles as Messengers from Reheating

Understand

Usually information from early eras such as reheating is hard to come by.

• In this paper we argue that, given the right circumstances, right-handed sterile neutrinos decaying to left-handed active ones at relatively late times can carry information from reheating by propagating freely over the thermal history.
• For not too small mixing angles, suitable right-handed neutrino masses are around ${\cal O}$(MeV-GeV).
• We identify the typical spectra and argue that they provide information on the ratio of the inflaton mass to the reheating temperature.