Primordial Helical Magnetic Fields from Inflation?

TL;DR

This paper investigates the generation of helical magnetic fields during inflation using stochastic inflation formalism, finding that stochastic effects limit the magnetic field amplitude, making it insufficient as seeds for cosmic magnetic fields.

Contribution

It introduces a stochastic inflation approach to helical magnetogenesis, revealing the impact of stochastic noise on magnetic field growth and equilibrium states.

Findings

Magnetic fields settle into a smaller equilibrium amplitude due to stochastic effects.

The model does not produce sufficiently strong seed fields for galactic dynamo amplification.

Stochastic dynamics balance tachyonic growth, preventing large magnetic field amplification.

Abstract

We revisit the mechanism of helical magnetogenesis during inflation with a parity violating interaction using the formalism of stochastic inflation. One of the polarization of the gauge field undergoes tachyonic growth leading to the generation of helical magnetic fields. We obtain the Langevin equations associated with the electromagnetic fields which are in the form of Ornstein-Uhlenbeck stochastic differential equations. Consequently, the tachyonic growth of the helical magnetic fields is balanced by a mean-reverting process of stochastic dynamics such that the magnetic fields settle down to an equilibrium state with the amplitude smaller than what is obtained in the absence of the stochastic noises. Working in the parameter space of the model where both the backreaction and the strong coupling problems are under control the model does not provide large enough seed to be amplified by the galactic dynamo as the source of the magnetic fields observed on cosmological scales.