Generation of helical magnetic fields from inflation

TL;DR

This paper investigates the generation of helical magnetic fields during inflation via axial coupling, concluding that such fields cannot reach observed strengths on large scales despite their evolution.

Contribution

It demonstrates that axial coupling during inflation produces a blue spectrum of magnetic fields that are insufficiently strong on cosmological scales.

Findings

Generated magnetic fields have a blue spectrum during inflation.

Evolved magnetic fields remain too weak to explain observed cosmic magnetic fields.

Axial coupling during inflation cannot produce the required large-scale magnetic fields.

Abstract

The generation of helical magnetic fields during single field inflation due to an axial coupling of the electromagnetic field to the inflaton is discussed. We find that such a coupling always leads to a blue spectrum of magnetic fields during slow roll inflation. Though the helical magnetic fields further evolve during the inverse cascade in the radiation era after inflation, we conclude that the magnetic fields generated by such an axial coupling can not lead to observed field strength on cosmologically relevant scales.