Cosmological magnetic fields from inflation in extended electromagnetism

TL;DR

This paper proposes an extended electromagnetic theory during inflation that generates primordial magnetic fields, which could serve as seeds for galactic magnetic fields observed today.

Contribution

It introduces a scalar state in electromagnetism that propagates and produces primordial magnetic fields during inflation, linking quantum fluctuations to cosmic magnetism.

Findings

Magnetic fields > 10^{-12} G generated on various scales

Effective charge density from quantum fluctuations during inflation

Generated magnetic fields could seed galactic dynamos

Abstract

In this work we consider an extended electromagnetic theory in which the scalar state which is usually eliminated by means of the Lorenz condition is allowed to propagate. This state has been shown to generate a small cosmological constant in the context of standard inflationary cosmology. Here we show that the usual Lorenz gauge-breaking term now plays the role of an effective electromagnetic current. Such a current is generated during inflation from quantum fluctuations and gives rise to a stochastic effective charge density distribution. Due to the high electric conductivity of the cosmic plasma after inflation, the electric charge density generates currents which give rise to both vorticity and magnetic fields on sub-Hubble scales. Present upper limits on vorticity coming from temperature anisotropies of the CMB are translated into lower limits on the present value of cosmic magnetic fields. We find that, for a nearly scale invariant vorticity spectrum, magnetic fields $B_{\lambda}> 10^{-12}$ G are typically generated with coherence lengths ranging from sub-galactic scales up to the present Hubble radius. Those fields could act as seeds for a galactic dynamo or even account for observations just by collapse and differential rotation of the protogalactic cloud.