Boosted Neutrinos and Relativistic Dark Particles as Messengers from Reheating

TL;DR

This paper proposes that late-decaying right-handed sterile neutrinos and relativistic dark particles can carry information from the early universe's reheating phase, potentially detectable by IceCube and explaining high-energy cosmic events.

Contribution

It introduces a novel mechanism where neutrinos and dark particles serve as messengers from reheating, linking early universe parameters to observable signals.

Findings

Neutrino spectra encode the ratio of inflaton mass to reheating temperature.

Primordial neutrino signals could be detected by IceCube.

Relativistic dark particles may explain PeV events and address the H0 tension.

Abstract

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. This primordial neutrino signal can be strong enough that it can be detected in IceCube. More speculatively, for a reheating temperature and inflaton mass satisfying $T_R={\cal O}(1-100)\, {\rm MeV}$, and $m_\phi={\cal O}(10^{16-19})\,$GeV they may even explain the observed PeV events. Also more general relativistic dark particles can play the role of such messengers, potentially not only allowing for the PeV events but also alleviating the $H_0$-tension .