Mode Spectrum of the Electromagnetic Field in Open Universe Models

TL;DR

This paper investigates the electromagnetic mode spectrum in open universe models, finding no supercurvature modes and thus constraining the evolution of cosmological magnetic fields without new physics.

Contribution

It demonstrates that electromagnetic fields in certain open universe models lack supercurvature modes, contrasting with scalar fields, and clarifies implications for magnetic field evolution.

Findings

No supercurvature modes in electromagnetic spectrum

Constraints on superadiabatic magnetic field evolution

Implications for cosmological magnetic field theories

Abstract

We examine the mode functions of the electromagnetic field on spherically symmetric backgrounds with special attention to the subclass which allows for the foliation as open Friedmann-Lemaitre (FL) spacetime. 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.