Gravitational charge production

TL;DR

This paper introduces a novel gravitational chargegenesis mechanism that generates primordial charge asymmetries through a coupling of a conserved current to the Ricci scalar during reheating, explaining the Universe's baryon asymmetry.

Contribution

It proposes a new gravitational sector interaction for charge generation, expanding on gravitational baryogenesis concepts with a detailed, minimal model compatible with inflation.

Findings

Successful explanation of baryon asymmetry via gravitational chargegenesis

Demonstration of a coupling to Ricci scalar producing effective chemical potentials

Compatibility with inflationary cosmology

Abstract

Wash-in leptogenesis is an attractive mechanism to produce the baryon asymmetry of the Universe. It treats right-handed-neutrino interactions as spectator processes, on the same footing as electroweak sphalerons, that reprocess primordial charge asymmetries in the thermal plasma into a baryon-minus-lepton asymmetry. The origin of these primordial charges must be accounted for by new $CP$-violating dynamics at very high energies. In this paper, we propose such a scenario of chargegenesis that, unlike earlier proposals, primarily relies on new interactions in the gravitational sector. We point out that a coupling of a conserved current to the divergence of the Ricci scalar during reheating can lead to nonzero effective chemical potentials in the plasma that, together with a suitable charge-violating interaction, can result in the production of a primordial charge asymmetry. Gravitational chargegenesis represents a substantial generalization of the idea of gravitational baryogenesis. We provide a detailed analysis of a generic and minimal realization that is consistent with inflation and show that it can successfully explain the baryon asymmetry of the Universe.