Primordial magnetic seed field amplification by gravitational waves: comment on gr-qc/0503006

TL;DR

This paper critiques a previous study on the amplification of primordial magnetic fields by gravitational waves, clarifying scale assessment issues and examining gauge-invariance and nonlinearity effects to refine understanding of the process.

Contribution

It provides a critical re-evaluation of prior results, correcting scale assessments and analyzing gauge-invariance and nonlinearity in the context of magnetic field amplification.

Findings

Incorrect scale assessment in prior work was identified.

Proper scale assessment alters the physical and numerical conclusions.

Gauge-invariance and nonlinearity considerations are crucial for accurate modeling.

Abstract

We consider the amplification of cosmological magnetic fields by gravitational waves as it was recently presented in [gr-qc/0503006]. That study confined to infinitely conductive environments, arguing that on spatially flat Friedmann backgrounds the gravito-magnetic interaction proceeds always as if the universe were a perfect conductor. We explain why this claim is not correct and then re-examine the Maxwell-Weyl coupling at the limit of ideal magnetohydrodynamics. We find that the scales of the main results of [gr-qc/0503006] were not properly assessed and that the incorrect scale assessment has compromised both the physical and the numerical results of the paper. This comment aims to clarify these issues on the one hand, while on the other it takes a closer look at the gauge-invariance and the nonlinearity of [gr-qc/0503006].