Gravitational leptogenesis from metric perturbations

TL;DR

This paper proposes a gravitational leptogenesis mechanism that leverages metric perturbations in the early universe to generate matter-antimatter asymmetry without new axial couplings, with potential observational relevance.

Contribution

It demonstrates that metric perturbations alone can induce leptogenesis via the Pontryagin density, offering a novel approach without additional couplings.

Findings

Asymmetry can match observations in certain scenarios

Generated matter-antimatter regions are smaller than the Hubble radius

The mechanism works across various inflationary and reheating models

Abstract

In this work we make the observation that the gravitational leptogenesis mechanism can be implemented without invoking new axial couplings in the inflaton sector. We show that in the perturbed Robertson-Walker background emerging after inflation, the spacetime metric itself breaks parity symmetry and generates a non-vansihing Pontryagin density which can produce a matter-antimatter asymmetry. We analyze the produced asymmetry in different inflationary and reheating scenarios. We show that the generated asymmetry can be locally comparable to observations in certain cases, although the size of the matter-antimatter regions is typically much smaller than the present Hubble radius.