Gravitational leptogenesis with kination and gravitational reheating

TL;DR

This paper examines gravitational leptogenesis during inflation with a Chern-Simons coupling, finding it insufficient under standard reheating but viable with kination scenarios like k- and G-inflation.

Contribution

It analyzes the viability of gravitational leptogenesis with Chern-Simons coupling, incorporating ghost mode constraints and exploring kination reheating to generate sufficient baryon asymmetry.

Findings

Standard reheating scenarios cannot produce enough baryon asymmetry.

Kination scenarios like k- and G-inflation can generate sufficient asymmetry.

Model parameters are constrained by ghost mode absence below the Planck scale.

Abstract

We revisit the gravitational leptogenesis scenario in which the inflaton is coupled to gravity by the Chern-Simons term and the lepton asymmetry is generated through the gravitational anomaly in the lepton number current during inflation. We constrain the possible model parameter space by requiring the absence of ghost modes below the Planck scale, which would suggest the breakdown of the effective theory, and evaluate the net baryon asymmetry for various reheating processes. We find that the mechanism with these requirements is insufficient to explain the observed baryon asymmetry of the Universe for standard reheating scenarios. We show that, however, with the kination scenario realized in e.g. the k- and G-inflation models, a sufficient baryon asymmetry can be generated within a feasible range of the model parameters.