Geometrical generation of cosmic magnetic fields within standard electromagnetism

Abstract

We study the evolution of cosmological magnetic fields in FRW models with curved spatial sections and outline a geometrical mechanism for their superadiabatic amplification on large scales. The mechanism operates within standard electromagnetic theory and applies to FRW universes with open spatial sections. We discuss the general relativistic nature of the effect and show how it modifies the adiabatic magnetic evolution by reducing the depletion rate of the field. Assuming a universe that is only marginally open today (i.e. for 1 − Ω 0 ∼ 10 −2 ), we estimate the main features of the superadiabatically amplified residual field and find that is of astrophysical interest.

Non-conformal evolution of magnetic fields during reheating

“…Neither of the two major paradigms proposed to attack this question, namely dynamo amplification and primordial origin, seems to be able to provide a solution by itself [4]. It therefore seems likely that both mechanisms are at work, i.e., a seed field is generated early in the cosmic evolution and then subjected to one or several amplification stages [5,6]. This calls for a careful analysis of the cosmological history of magnetic fields [7].…”