Dynamics of Long-lived Axion Domain Walls and Its Cosmological Implications

TL;DR

This paper updates the understanding of long-lived axion domain wall networks by simulating their evolution, identifying energy loss mechanisms, and calculating their contribution to axion dark matter, revealing significant discrepancies with previous models.

Contribution

It introduces a new simulation and analytical approach to model axion domain wall dynamics and their impact on dark matter abundance, highlighting notable differences from earlier studies.

Findings

Identification of dominant energy loss mechanisms for axion domain walls

Calculation of axion spectra emitted from the domain wall network

Revised predictions for axion dark matter density and abundance

Abstract

We perform an updated analysis on a long-lived axion domain wall (DW) network. By simulating the axion field on a 3D lattice and fitting an analytical model for the DW evolution, we identify the leading energy loss mechanisms of the DWs and compute the spectrum of axions emitted from the network. The contribution from the DWs to axion dark matter (DM) density is derived, with viable parameter space given. The application to both QCD axions and general axion-like particles (ALPs) are considered. Due to the new approaches taken, while our results bear consistency with earlier literature, notable discrepancies are also revealed, such as the prediction for DM abundance, which may have a profound impact on axion phenomenology at large.