Post-inflationary leptogenesis and dark matter production: metric versus Palatini formalism

Abstract

We investigate production of non-thermal dark matter particles and heavy sterile neutrinos from inflaton during the reheating era, which is preceded by a slow-roll inflationary epoch with a quartic potential and non-minimal coupling (ξ) between inflaton and gravity. We compare our analysis between metric and Palatini formalism. For the latter, the tensor-to-scalar ratio, r, decreases with ξ. We find that for ξ = 0.5 and number of e-folds ~ 60, r can be as small as ~ $$ \mathcal{O} $$ O (10−3) which may be validated at future reaches of upcoming CMB observation such as CMB-S4 etc. We identify the permissible range of Yukawa coupling yχ between inflaton and fermionic DM χ, to be $$ \mathcal{O} $$ O (10−3.5) ≳ yχ ≳ $$ \mathcal{O} $$ O (10−20) for metric formalism and $$ \mathcal{O} $$ O (10−4) ≳ yχ ≳ $$ \mathcal{O} $$ O (10−11) for Palatini formalism which is consistent with current PLANCK data and also within the reach of future CMB experiments. For the scenario of leptogenesis via the decay of sterile neutrinos produced from inflaton decay, we also investigate the parameter space involving heavy neutrino mass MN1 and Yukawa coupling yN1 of sterile neutrino with inflaton, which are consistent with current CMB data and successful generation of the observed baryon asymmetry of the universe via leptogenesis. In contrast to metric formalism, in the case of Palatini formalism, for successful leptogenesis to occur, we find that yN1 has a very narrow allowable range and is severely constrained from the consistency with CMB predictions.