Long-term dynamics of cosmological axion strings

TL;DR

This study uses advanced, long-duration field-theoretic simulations to analyze the long-term evolution of cosmological axion strings, revealing non-scaling behavior and dependence on symmetry-breaking scales.

Contribution

It provides the longest and most detailed simulation of axion string dynamics, showing deviations from the traditional scaling solution and dependence on the Peccei-Quinn symmetry-breaking scale.

Findings

Global strings' scaling parameter increases logarithmically over time.

Scaling parameter depends nontrivially on the Peccei-Quinn symmetry-breaking scale.

Extended simulations enable monitoring of string network dynamics over unprecedented durations.

Abstract

We present results of new field-theoretic simulation of cosmological axion strings, which are eight times longer than previous ones. We have upgraded our simulation of physical strings in Hiramatsu et al. (2011) in terms of the number of grids as well as the suite of analysis methods. These improvements enable us to monitor a variety of quantities characterizing the dynamics of the physical string network for the longest term ever. Our extended simulations have revealed that global strings do not evolve according to the scaling solution but its scaling parameter, or the number of long strings per horizon, increases logarithmically in time. In addition, we have also found that the scaling parameter shows nontrivial dependence on the breaking scale of the Peccei-Quinn symmetry.