Stochastic gravitational waves from narrow-band cosmological magnetic fields

We calculate the spectrum of gravitational waves generated by a cosmological magnetic field with a narrow-band power spectrum. For a spectrum narrowly peaked at a comoving wavenumber $k_c$, we find that the gravitational wave signal peaks at $2k_c$ and has a sharp cutoff at this scale. We apply this result to an ultralight dark matter model of magnetogenesis operating around recombination, in which an axion-photon coupling generates a helical magnetic field by parametric resonance. We determine the conditions for the resulting gravitational waves to enter the frequency range of pulsar timing experiments. Although the required frequency can be reached for sufficiently large coupling, the corresponding amplitude is below the experimental sensitivity for physically allowed energy densities of the magnetic field. We generalize this conclusion to models of magnetogenesis operating at other epochs, estimating as $T \simeq 160 \mathrm{MeV}$ the temperature of a magnetogenesis process assumed to be the source of the stochastic gravitational wave background suggested by pulsar timing arrays. We place the lower bound $T \gtrsim 1$-$10 \mathrm{MeV}$ on such viable models.

Preparing paper insights from the available abstract and paper details.

Authors

Abdias Aires; Tatsuya Daniel

Published

Oct 8, 2026

Paper type

preprint

Source

Arxiv