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arXiv · 2602.04285

Parametric Resonance and Backreaction Effects in Magnetogenesis from Ultralight Dark Matter

Nirmalya Brahma·Robert Brandenberger
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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.

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Nirmalya Brahma, Robert Brandenberger. 2026-02-04. Parametric Resonance and Backreaction Effects in Magnetogenesis from Ultralight Dark Matter. https://arxiv.org/abs/2602.04285

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