Gradient models of the axion-photon coupling

TL;DR

This paper introduces an extended axion-photon coupling model incorporating gradient terms and applies it to cosmological scenarios, analyzing early Universe magnetic dominance and late-time accelerated expansion.

Contribution

It develops a novel gradient-based axion-photon coupling model and explores its implications in cosmology, including analytical, qualitative, and numerical analyses.

Findings

Early Universe dominated by magnetic fields

Induced electric fields from axion-photon interaction

Insights into late-time accelerated expansion

Abstract

We establish an extended version of the Einstein - Maxwell - axion model by introducing into the Lagrangian cross-terms, which contain the gradient four-vector of the pseudoscalar (axion) field in convolution with the Maxwell tensor. The gradient model of the axion-photon coupling is applied to cosmology: we analyze the Bianchi-I type Universe with an initial magnetic field, electric field induced by the axion-photon interaction, cosmological constant and dark matter, which is described in terms of the pseudoscalar (axion) field. Analytical, qualitative and numerical results are presented in detail for two distinguished epochs: first, for the early Universe with magnetic field domination; second, for the stage of late-time accelerated expansion.