Boosted Neutrinos and Relativistic Dark Particles as Messengers from Reheating

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 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 = O(1 − 100) MeV, and m φ = 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.

The Spectrum of Dark Radiation as a Probe of Reheating

“…In a general setup, the messengers can be produced from inflaton or modulus decays. In a previous paper by the present authors [32], the transparency condition of the Universe for the messengers, including neutrinos and relativistic dark particles, were clarified. Satisfying these conditions, they can travel over the thermal history until today, and the momentum distributions carry the information of the mother particles and thus can be messengers of the reheating.…”

“…One way to overcome this challenge could be very weakly interacting particles that are created during reheating and freely propagate until today. Suitable "messengers" may be gravitons/gravitational waves [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27], axion-like particles (ALPs) [28][29][30][31], right handed neutrinos [32] or some other very weakly interacting new particle. Preferably, such a messenger should remain relativistic until today, thereby constituting dark radiation.…”

“…[30] even already calculated the energy spectrum of the ALPs and gave analytic expressions for decays taking place in ei-ther pure matter or radiation domination 1 ). In [32] we discussed further possibilities such as right-handed neutrinos and more general messengers in dark matter, neutrino, and cosmic microwave background experiments.…”

“…Beyond the ability to detect the messenger particles the next task is to establish their origin from reheating and to obtain additional information. One feature of the messenger spectrum from reheating is the isotropic angular distribution which can be distinguished from particle spectra from galactic sources [30,32]. However, an isotropic distribution arises as long as the decays of heavy non-relativistic particles happens much before today [34,35].…”

On the reactions involving neutrinos and hidden mass particles in hypercolor model

“…Then three secondary neutrinos are produced and can be accompanied with the accelerated DM particle. This process can be informative especially because both of these neutral objects can be messengers from regions of high DM density -regions near AGN or from possible DM inhomogeneities of some other nature -and early epoch of the Universe [45]. Work on analysis of such reactions is in progress.…”