Non-conformal evolution of magnetic fields during reheating

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. *

Holography of Little Inflation

“…The Hawking-Page transition can be restored, at any desired temperature, by compactifying the planar event horizon to a torus [41]; in our case it would be natural to choose it to occur at the temperature at which the cosmic plasma crosses the phase line. 5 Alternative possible evolution laws for B have been proposed [42][43][44], but are controversial [45][46][47]; if they can arise, they can probably only do so before the plasma era we are studying here [48]. During the plasma era, such "superadiabatic amplification" can be reconciled with a holographic bound [31] only with difficulty; see below.…”