Parametric Resonance and Backreaction Effects in Magnetogenesis from Ultralight Dark Matter

TL;DR

This paper investigates the magnetogenesis mechanism driven by ultralight dark matter, analyzing parametric resonance channels and back-reaction effects, concluding that the process can generate cosmologically relevant magnetic fields despite back-reaction.

Contribution

It introduces a detailed analysis of narrow parametric resonance and back-reaction effects in ultralight dark matter-induced magnetogenesis, expanding on previous tachyonic resonance models.

Findings

Narrow resonance channel exists with a Floquet exponent slightly smaller than tachyonic resonance.

For very small coupling constants, tachyonic resonance becomes ineffective, and narrow resonance dominates.

Back-reaction effects are manageable, allowing a significant fraction of dark matter density to convert into magnetic fields.

Abstract

We take a more detailed look at the recently proposed magnetogenesis mechanism triggered by ultralight dark matter coupled to electromagnetism. The proposed mechanism made use of a tachyonic resonance channel which leads to the exponential amplification of infrared modes. Here, we first investigate a possible narrow band parametric resonance channel which can produce photons at higher frequencies. Secondly, we estimate the effects of back-reaction on terminating the resonance. We find that there is indeed a narrow resonance channel. It is characterized by a Floquet exponent which is slightly smaller than the corresponding exponent for the tachyonic resonance. However, there is a region of parameter space (corresponding to a very small coupling constant) for which the tachyonic resonance is ineffective. In this case, the narrow resonance will dominate, and it will still be sufficiently strong to generate the observed magnetic fields on cosmological scales. Our analytical treatment of the back-reaction effects considered here indicates that a fraction of order one of the initial dark matter density can flow into the gauge fields. Hence, our magnetogenesis scenario appears to be robust to back-reaction effects.