Late Time Magnetogenesis from Ultralight Scalar Dark Matter

TL;DR

This paper proposes a mechanism where ultralight scalar dark matter induces a tachyonic instability in gauge fields, leading to the generation of cosmologically significant magnetic fields at late times.

Contribution

It introduces a novel late-time magnetogenesis scenario driven by ultralight scalar dark matter coupled to electromagnetism, explaining observed cosmic magnetic fields.

Findings

Magnetic fields of sufficient amplitude are generated on cosmological scales.

The mechanism relies on a tachyonic instability caused by scalar-dark matter oscillations.

The model aligns with current observational constraints.

Abstract

Assuming that Dark Matter is an ultralight scalar field which is coupled to electromagnetism via a gauge-kinetic function and which at the time of recombination is oscillating coherently over a Hubble patch, we show that there is a tachyonic instability for the gauge field modes which leads to the generation of magnetic fields on cosmological scales of sufficient amplitude to explain observations.