Axion domain walls and thermal friction

TL;DR

This paper introduces a new analytical approach using nonequilibrium quantum field theory to study axion domain wall networks, aiming to improve predictions of axion dark matter abundance beyond traditional numerical simulations.

Contribution

It presents a novel analytical framework based on the two-particle-irreducible effective action to model axion domain wall dynamics, addressing limitations of previous simulation-based methods.

Findings

Preliminary results demonstrate the framework's potential for accurate axion abundance predictions.

The approach incorporates thermal, self-interaction, plasma, and quantum effects.

It offers a systematic way to analyze the evolution of topological defect networks.

Abstract

The post-inflationary Peccei-Quinn symmetry-breaking scenario provides a rich theoretical framework to study axion dark matter production through the dynamics oftopological defects. Accurate predictions for the axion abundance require a detailed understanding of the formation and evolution of cosmic strings and domain walls, which are inevitably produced in this scenario. Most existing studies rely on large-scale numerical simulations of the classical equations of motion, which are subject to significant systematic uncertainties. In this contribution, we briefly review the main features of the post-inflationary scenario and the current limitations in the literature, and present preliminary results from a new analytical framework for axion domain wall networks. Our approach is based on nonequilibrium quantum field theory. It employs the two-particle-irreducible effective action to derive effective Fokker-Planck equations for macroscopic quantities such as the average energy density and root-mean-square velocity of the network.We discuss the relevance of thermal, self-interactions, plasma-induced and quantum effects for cosmological axion abundance estimates, with applications to QCD axions and high-mass axion-like particles.