Lattice simulations of Abelian gauge fields coupled to axions during inflation

Abstract

We use a lattice simulation to study a model of axion inflation where the inflaton is coupled to a U(1) gauge field through Chern-Simons interaction. These kinds of models have already been studied with a lattice simulation in the context of reheating. In this work, we focus on the deep inflationary phase and discuss the new aspects that need to be considered in order to simulate gauge fields in this regime. Our main result is reproducing with precision the growth of the gauge field on the lattice induced by the rolling of the axion on its potential, thus recovering the results of linear perturbation theory for this model. In order to do so, we study in detail how the spatial discretization, through the choice of the spatial derivatives on the lattice, influences the dynamics of the gauge field. We find that the evolution of the gauge field is highly sensitive to the choice of the spatial discretization scheme. Nevertheless, we are able to identify a discretization scheme for which the growth of the gauge field on the lattice reproduces the one of continuous space with good precision.