Mode spectrum of the electromagnetic field in open universe models

Abstract

We examine the mode functions of the electromagnetic field on spherically symmetric backgrounds with special attention to the subclass which allows for a foliation as open Friedmann-Lemaître (FL) space-time. It is well known that in certain scalar field theories on open FL background there can exist so-called supercurvature modes, their existence depending on parameters of the theory. Looking at specific open universe models, such as open inflation and the Milne universe, we find that no supercurvature modes are present in the spectrum of the electromagnetic field. This excludes the possibility for superadiabatic evolution of cosmological magnetic fields within these models without relying on new physics or breaking the conformal invariance of electromagnetism. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.