Homogeneous and isotropic cosmologies with nonlinear electromagnetic radiation

TL;DR

This paper investigates cosmological models with nonlinear electromagnetic radiation, showing how electric and magnetic fields influence universe evolution, including singularities and accelerated expansion, within various nonlinear electrodynamics theories.

Contribution

It demonstrates the effects of electric fields in nonlinear electrodynamics cosmologies, extending previous magnetic universe models to include electric components and their impact on universe dynamics.

Findings

For Born-Infeld electrodynamics, the equation of state remains close to 1/3.

Electric fields eliminate the bounce, leading to an initial singularity.

Electric fields restrict late-time accelerated expansion to cases where E^2<3B^2.

Abstract

In this paper I examine cosmological models that contain a stochastic background of nonlinear electromagnetic radiation. I show that for Born-Infeld electrodynamics the equation of state parameter, $w=P/\rho$, remains close to 1/3 throughout the evolution of the universe if $E^2=B^2$ in the late universe to a high degree of accuracy. Theories with electromagnetic Lagrangians of the form $L=-{1/4}F^2+\alpha F^4$ have recently been studied in magnetic universes, where the electric field vanishes. It was shown that the $F^4$ term can produce a bounce in the early universe, avoiding an initial singularity. Here I show that the inclusion of an electric field, with $E^2\simeq B^2$ in the late universe, eliminates the bounce and the universe "begins" in an initial singularity. I also examine theories with Lagrangians of the form $L=-{1/4}F^2-\mu^8/F^2$, which have been shown to produce a period of late time accelerated expansion in magnetic universes. I show that, if an electric field is introduced, the accelerated phase will only occur if $E^2<3B^2$.