Axion Fragmentation on the Lattice

TL;DR

This paper investigates axion fragmentation during field oscillations, comparing analytical and lattice simulation results, and explores potential cosmological implications of bubble formation with different axion field values.

Contribution

It provides a detailed comparison between linear analysis and lattice simulations of axion fragmentation, highlighting their agreement in stopping times and discussing cosmological effects.

Findings

Linear analysis and lattice simulations agree within an order of magnitude on stopping time

Axion fragmentation can lead to bubble formation with different VEVs

Potential cosmological consequences of axion bubbles are discussed

Abstract

We analyze the phenomenon of axion fragmentation when an axion field rolls over many oscillations of a periodic potential. This is particularly relevant for the case of relaxion, in which fragmentation provides the necessary energy dissipation to stop the field evolution. We compare the results of a linear analysis with the ones obtained from a classical lattice simulation, finding an agreement in the stopping time of the zero mode between the two within an ${\cal O}(1)$ difference. We finally speculate on the generation of bubbles with different VEVs of the axion field, and discuss their cosmological consequences.