Inflationary Birefringence and Baryogenesis

TL;DR

This paper explores how inflationary birefringence caused by axion-like inflaton fields coupled to gravity and gauge fields can generate lepton asymmetry and potentially produce observable circular polarization in the CMB, linking early universe physics to observable signals.

Contribution

It introduces a novel inflationary leptogenesis mechanism involving birefringent primordial perturbations from axion couplings, connecting leptogenesis with CMB polarization signatures.

Findings

Birefringent gravitational and gauge perturbations can generate lepton asymmetry during inflation.

Certain models predict observable circular polarization (V-mode) in the CMB.

The polarization cross-correlations relate to leptogenesis processes.

Abstract

A decade ago, the first leptogenesis model based on inflation was proposed, where the complex phase of the inflaton field carries lepton number. If the inflaton field is an axion, it can couple to gravitational waves and gauge fields via. Chern-Simons invariants. Due to these couplings, birefringent gravitational and gauge primordial perturbations are created during inflation to generate a lepton asymmetry, establishing a possible connection between non-vanishing TB-parity violating polarization cross-correlations and leptogenesis. We also discuss the prospect for a subset of these models can directly source circular (V-mode) polarization in the CMB.