Thermal and nonthermal dark matters with gravitational neutrino reheating

TL;DR

This paper explores how gravitationally produced neutrinos can reheat the universe and influence dark matter production, revealing new parameter spaces and potential experimental signatures in early universe cosmology.

Contribution

It introduces a detailed analysis of neutrino-driven reheating with gravitational interactions, linking dark matter production to Type-I seesaw parameters and observational constraints.

Findings

Reheating scenarios depend on seesaw parameters and equation of state.

Constraints on reheating equation of state from BBN and gravitational waves.

New dark matter parameter spaces accessible via freeze-in, freeze-out, or oscillation during reheating.

Abstract

We have discussed in detail how neutrinos produced from inflaton solely through gravitational interaction can successfully reheat the universe. For this, we have introduced the well-known Type-I seesaw neutrino model. Depending on seesaw model parameters, two distinct reheating histories have been realized and dubbed as i) Neutrino dominating: Following the inflaton domination, the universe becomes neutrino dominated, and their subsequent decay concludes the reheating process, and ii) Neutrino heating: Despite being sub-dominant compared to inflaton energy, neutrinos efficiently heat the thermal bath and produce the radiation dominated universe. Imposing baryon asymmetric yield, the $\Delta N_{\rm eff}$ constraint at Big Bang Nucleosynthesis (BBN) considering primordial gravitational waves (PGW), we have arrived at the following constraints on reheating equation of state to lie within $0.5\lesssim w_\phi\lesssim1.0$. In these neutrino-driven reheating backgrounds, we further performed a detailed analysis of both thermal and non-thermal production of dark matter (DM), invoking two minimal models, namely the Higgs portal DM and classical QCD pseudo scalar axion. An interesting correlation between seemingly uncorrelated DM and Type-I seesaw parameters has emerged when confronting various direct and indirect observations. When DMs are set to freeze-in, freeze-out, or oscillate during reheating, new parameter spaces open, which could be potentially detectable in future experiments, paving an indirect way to look into the early universe in the laboratory.