Gravitational Leptogenesis in the Axion Inflation with an SU(2) gauge field

TL;DR

This paper proposes a novel leptogenesis mechanism during axion inflation involving an SU(2) gauge field that generates matter-antimatter asymmetry through chiral gravitational waves and gravitational anomalies.

Contribution

It introduces an intrinsic leptogenesis process in axion inflation models with a classical SU(2) gauge field, linking gauge field fluctuations to matter asymmetry.

Findings

Generates sufficient lepton asymmetry to explain matter-antimatter imbalance.

Produces a small chiral tensor power spectrum on large scales.

Compatible with observed baryon-to-photon ratio.

Abstract

We present an intrinsic leptogenesis mechanism in models of axion inflation with a classical SU(2) gauge field. The gauge field is coupled to the axion with a Chern-Simons interaction and comprises a tiny fraction of the total energy, $\frac{\rho_{_{\rm YM}}}{\rho_{_{\rm tot}}}\lesssim\epsilon^2$. However, it has spin-2 fluctuations which breaks the parity and leads to the generation of chiral gravitational waves during inflation. By the gravitational anomaly in SM, it naturally creates a net lepton number density, sufficient to explain the matter asymmetry. We show that this mechanism can generate the observed value of baryon to photon number density in a natural range of parameters and yet has a small chiral tensor power spectrum on large scales.