Non-conformal evolution of magnetic fields during reheating

TL;DR

This paper investigates how electromagnetic fields evolve during the universe's reheating phase, considering second order causal hydrodynamics, revealing non-conformal effects that influence magnetic field behavior in early cosmology.

Contribution

It introduces a non-conformal hydrodynamic model for electromagnetic field evolution during reheating, highlighting effects of temperature gradients on magnetic fields.

Findings

Expansion-induced temperature gradients oppose Ohmic dissipation.

Hydrodynamic instabilities may evolve differently than in conformal models.

The theory suggests new patterns of magnetic field evolution in early universe.

Abstract

We consider the evolution of electromagnetic fields coupled to conduction currents during the reheating era after inflation, and prior to the establishing of the proton-electron plasma. We assume that the currents may be described by second order causal hydrodynamics. The resulting theory is not conformally invariant. The expansion of the Universe produces temperature gradients which couple to the current and generally oppose Ohmic dissipation. Although the effect is not strong, it suggests that the unfolding of hydrodynamic instabilities in these models may follow a different pattern than in first order theories, and even than in second order theories on non expanding backgrounds.