Gravitational Leptogenesis in Bounce Cosmology

TL;DR

This paper explores how gravitational leptogenesis can occur during an Ekpyrotic contraction phase in bounce cosmology, using couplings to Chern-Simons terms to generate chiral gravitational waves and lepton asymmetry.

Contribution

It demonstrates the viability of gravitational leptogenesis during Ekpyrotic contraction via two specific coupling mechanisms, expanding the understanding of baryogenesis in bounce cosmologies.

Findings

Successful leptogenesis is possible during Ekpyrotic contraction.

Chiral gravitational waves are produced through Chern-Simons couplings.

Lepton asymmetry can be converted into baryon asymmetry.

Abstract

We investigate whether successful Gravitational Leptogenesis can take place during an Ekpyrotic contraction phase. Two possible paths by which this can occur are coupling the Ekpyrotic scalar to a gravitational Chern-Simons term, or to a $ U(1) $ gauge field Chern-Simons term. These couplings lead to the production of chiral gravitational waves, which generate a lepton number asymmetry through the gravitational-lepton number anomaly. This lepton asymmetry is subsequently reprocessed by equilibrium sphaleron processes to produce a baryon asymmetry. We find successful Gravitational Leptogenesis to be possible in Ekpyrotic bounce cosmologies through both of these mechanisms.