Scale-invariant helical magnetic field evolution and the duration of inflation

TL;DR

This paper explores how measuring the helicity of primordial magnetic fields generated during inflation can set bounds on the inflation duration, supported by simulations showing structural differences in helical versus non-helical fields.

Contribution

It demonstrates that magnetic helicity density measurements can constrain the inflation period and uses simulations to analyze the structural evolution of helical magnetic fields.

Findings

Helical magnetic fields can provide lower bounds on inflation duration.

Simulations show similar development of scale-invariant fields with or without helicity.

Helical fields exhibit more pronounced folded structures in simulations.

Abstract

We consider a scale-invariant helical magnetic field generated during inflation. We show that, if the mean magnetic helicity density of such a field is measured, it can be used to determine a lower bound on the duration of inflation. Upper bounds can be used to derive constraints on the minimal duration of inflation if one assumes that the magnetic field generated during inflation is helical. Using three-dimensional simulations, we show that an initially scale-invariant field develops, which is similar both with and without magnetic helicity. In the fully helical case, however, the magnetic field appears to have a more pronounced folded structure.