Electromagnetic potentials in curved spacetimes

TL;DR

This paper develops a general relativistic framework for electromagnetic potentials in curved spacetimes, analyzing their wave equations, evolution in Friedmann universes, and interactions with gravitational waves, highlighting effects of spatial curvature.

Contribution

It derives wave equations for electromagnetic potentials in arbitrary curved spacetimes and explores their evolution and interaction with gravitational waves, emphasizing the role of spatial geometry.

Findings

Potential evolution differs between closed and open Friedmann models due to spatial curvature.

Electromagnetic potentials can be resonantly amplified by gravitational waves in low-density environments.

Wave equations explicitly include curvature effects, influencing electromagnetic behavior in cosmological settings.

Abstract

Electromagnetic potentials allow for an alternative description of the Maxwell field, the electric and magnetic components of which emerge as gradients of the vector and the scalar potential. We provide a general relativistic analysis of these potentials, by deriving their wave equations in an arbitrary Riemannian spacetime containing a generalised imperfect fluid. Some of the driving agents in the resulting wave formulae are explicitly due to the curvature of the host spacetime. Focusing on the implications of non-Euclidean geometry, we look into the linear evolution of the vector potential in Friedmann universes with nonzero spatial curvature. Our results reveal a qualitative difference in the evolution of the potential between the closed and the open Friedmann models, solely triggered by the different spatial geometry of these spacetimes. We then consider the interaction between gravitational and electromagnetic radiation and the effects of the former upon the latter. In so doing, we apply the wave formulae of both potentials to a Minkowski background and study the Weyl-Maxwell coupling at the second perturbative level. Our solutions, which apply to low-density interstellar environments away from massive compact stars, allow for the resonant amplification of both the electromagnetic potentials by gravitational-wave distortions.