Gravito-magnetic amplification in cosmology

TL;DR

This paper investigates how gravitational waves influence cosmic magnetic fields, revealing that conductivity levels determine whether magnetic fields are amplified or resonantly enhanced through gravito-magnetic interactions.

Contribution

It provides an analytical, gauge-invariant study of gravito-magnetic coupling in cosmology, highlighting the dependence on medium conductivity and identifying conditions for superadiabatic and resonant magnetic field amplification.

Findings

High conductivity leads to superadiabatic magnetic field amplification.

Poor conductivity environments can cause resonant amplification of magnetic fields.

Magnetic field oscillations diverge when gravitational wave and magnetic field wavelengths match.

Abstract

Magnetic fields interact with gravitational waves in various ways. We consider the coupling between the Weyl and the Maxwell fields in cosmology and study the effects of the former on the latter. The approach is fully analytical and the results are gauge-invariant. We show that the nature and the outcome of the gravito-magnetic interaction depends on the electric properties of the cosmic medium. When the conductivity is high, gravitational waves reduce the standard (adiabatic) decay rate of the B-field, leading to its superadiabatic amplification. In poorly conductive environments, on the other hand, Weyl-curvature distortions can result into the resonant amplification of large-scale cosmological magnetic fields. Driven by the gravitational waves, these B-fields oscillate with an amplitude that is found to diverge when the wavelengths of the two sources coincide. We present technical and physical aspects of the gravito-magnetic interaction and discuss its potential implications.