A non-perturbative study of the evolution of cosmic magnetised sources

TL;DR

This paper presents a non-perturbative hydrodynamical analysis of how primordial magnetic fields influence the evolution of the early universe's cosmic fluid, considering multiple particle species and anisotropic models.

Contribution

It introduces a non-perturbative framework for studying the evolution of cosmic magnetic fields within an anisotropic cosmological model, extending beyond linear perturbation methods.

Findings

Magnetic fields lead to a near FLRW evolution consistent with observational bounds.

The evolution of the cosmic fluid remains roughly comparable to weak field linear approximations.

The approach offers insights into non-perturbative interactions between magnetic fields and cosmic matter.

Abstract

We undertake a hydrodynamical study of a mixture of tightly coupled primordial radiation, neutrinos, baryons, electrons and positrons, together with a gas of already decoupled dark matter WIMPS and an already existing "frozen" magnetic field in the infinite conductivity regime. Considering this cosmic fluid as the source of a homogeneous but anisotropic Bianchi I model, we describe its interaction with the magnetic field by means of suitable equations of state that are appropriate for the particle species of the mixture between the end of the leptonic era and the beginning of the radiation-dominated epoch. Fulfilment of observational bounds on the magnetic field intensity yields a "near FLRW" (but strictly non-perturbative) evolution of the geometric, kinematic and thermodynamical variables. This evolution is roughly comparable to the weak field approximation in linear perturbations on a spatially flat FLRW background of sources in which the frozen magnetic fields are coherent over very large supra-horizon scales. Our approach and results may provide interesting guidelines in potential situations in which non-perturbative methods are required to study the interaction between magnetic fields and the cosmic fluid.