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Gravitational Waves from an Axion-Dark Photon System: A Lattice Study

by Wolfram Ratzinger, Pedro Schwaller, Ben A. Stefanek

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Submission summary

As Contributors: Pedro Schwaller
Preprint link: scipost_202104_00020v1
Date accepted: 2021-06-18
Date submitted: 2021-04-19 12:14
Submitted by: Schwaller, Pedro
Submitted to: SciPost Physics
Academic field: Physics
  • High-Energy Physics - Theory
  • High-Energy Physics - Phenomenology
  • Cosmology and Nongalactic Astrophysics
Approach: Theoretical


In this work, we present a lattice study of an axion - dark photon system in the early Universe and show that the stochastic gravitational wave (GW) background produced by this system may be probed by future GW experiments across a vast range of frequencies. The numerical simulation on the lattice allows us to take into account non-linear backreaction effects and enables us to accurately predict the final relic abundance of the axion or axion-like particle (ALP) as well as its inhomogeneities, and gives a more precise prediction of the GW spectrum. Importantly, we find that the GW spectrum has more power at high momenta due to $2\rightarrow1$ processes. Furthermore, we find the degree of polarization of the peak of the GW spectrum depends on the ALP-dark photon coupling and that the polarization can be washed out or even flipped for large values thereof. In line with recent results in the literature, we find the ALP relic abundance may be suppressed by two orders of magnitude and discuss possible extensions of the model that expand the viable parameter space. Finally, we discuss the possibility to probe ultralight ALP dark matter via spectral distortions of the CMB.

Published as SciPost Phys. 11, 001 (2021)

Reports on this Submission

Anonymous Report 1 on 2021-4-20 (Invited Report)


The reply of the authors to the referee report is satisfactory. The new version of the manuscript meets the acceptance criteria of the Journal and I recommend it for publication.

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