Baryogenesis from Decaying Magnetic Helicity in Axiogenesis

TL;DR

This paper explores how axion-related instabilities in the early universe can generate magnetic fields that lead to baryon asymmetry, providing a novel mechanism for baryogenesis linked to axion dark matter.

Contribution

It introduces a new baryogenesis mechanism via decaying magnetic helicity in axiogenesis, connecting axion dark matter production with baryon asymmetry generation.

Findings

Helical magnetic fields can be produced by axion instabilities.

These magnetic fields can source baryon asymmetry at the electroweak transition.

Constraints on axion parameters are derived from baryon overproduction.

Abstract

Generating axion dark matter through the kinetic misalignment mechanism implies the generation of large asymmetries for Standard Model fermions in the early universe. Even if these asymmetries are washed out at later times, they can trigger a chiral plasma instability in the early universe. Similarly, a direct coupling of the axion with the hypercharge gauge field can trigger a tachyonic instability. These instabilities produce helical magnetic fields, which are preserved until the electroweak phase transition. At the electroweak phase transition, these become a source of baryon asymmetry, which can be much more efficient than the original axiogenesis proposal. We discuss constraints on axion dark matter production from the overproduction of the baryon asymmetry as well as a minimal, albeit fine-tuned setup, where both the correct dark matter abundance and baryon asymmetry can be achieved. For a given axion decay constant, this leads to a sharp prediction for the mass of the radial direction of the Peccei Quinn field, which is a soft mass scale in supersymmetric theories.