Dark energy, non-minimal couplings and the origin of cosmic magnetic fields

TL;DR

This paper explores a generalized electromagnetic theory in curved space-time with non-minimal couplings, proposing that dark energy-related electromagnetic backgrounds can generate cosmic magnetic fields and relate magnetic moments to angular momentum.

Contribution

It introduces a comprehensive electromagnetic framework incorporating non-minimal couplings and demonstrates how dark energy can produce seed magnetic fields and influence magnetic moments of compact objects.

Findings

Dark energy background can generate seed magnetic fields up to 10^{-9} G in galaxies.

The theory predicts magnetic moments of rotating objects relate to their angular momentum.

Electromagnetic theory reduces to standard electromagnetism with an effective current in the weak-field limit.

Abstract

In this work we consider the most general electromagnetic theory in curved space-time leading to linear second order differential equations, including non-minimal couplings to the space-time curvature. We assume the presence of a temporal electromagnetic background whose energy density plays the role of dark energy, as has been recently suggested. Imposing the consistency of the theory in the weak-field limit, we show that it reduces to standard electromagnetism in the presence of an effective electromagnetic current which is generated by the momentum density of the matter/energy distribution, even for neutral sources. This implies that in the presence of dark energy, the motion of large-scale structures generates magnetic fields. Estimates of the present amplitude of the generated seed fields for typical spiral galaxies could reach $10^{-9}$ G without any amplification. In the case of compact rotating objects, the theory predicts their magnetic moments to be related to their angular momenta in the way suggested by the so called Schuster-Blackett conjecture.