Magnetic fields from inflation: the transition to the radiation era

TL;DR

This paper analyzes how magnetic fields generated during inflation influence scalar metric perturbations, revealing a unique constant mode that could cause observable non-Gaussianities in the CMB.

Contribution

It introduces the calculation of inflation-generated magnetic field contributions to scalar perturbations, highlighting a new constant mode absent in post-inflationary scenarios.

Findings

Magnetic fields from inflation contribute to scalar metric perturbations.

A new constant mode from inflationary magnetic fields is identified.

Potential for significant non-Gaussian CMB anisotropies.

Abstract

We compute the contribution to the scalar metric perturbations from large-scale magnetic fields which are generated during inflation. We show that apart from the usual passive and compensated modes, the magnetic fields also contribute to the constant mode from inflation. This is different from the causal (post inflationary) generation of magnetic fields where such a mode is absent and it might lead to significant, non-Gaussian CMB anisotropies.