Sensitivities on non-spinning and spinning primordial black hole dark matter with global 21 cm troughs

TL;DR

This paper explores how measurements of the global 21 cm signal can constrain primordial black hole dark matter, showing that future detections could provide strong evidence for or against PBHs as dark matter candidates.

Contribution

It analyzes the sensitivity of 21 cm observations to both non-spinning and spinning primordial black holes, highlighting potential improvements with astrophysical uncertainties.

Findings

Sensitivity of 21 cm signals to PBH densities is competitive with other methods.

Detection of 21 cm absorption troughs can strongly constrain PBH dark matter.

Sensitivity depends significantly on astrophysical parameters.

Abstract

Detection of the global 21 cm signal arising from neutral hydrogen can revolutionize our understanding of the standard evolution of the universe after recombination. In addition, it can also be an excellent probe of Dark Matter (DM). Among all the DM candidates, Primordial Black Holes (PBHs) are one of the most well-motivated. Hawking emission from low-mass PBHs can have substantial effect on the thermal and ionization history of the early universe, and that in turn can have an imprint on the global 21 cm signal. Recently EDGES has claimed a global 21 cm signal, though SARAS 3 has rejected that claim. In this work, we investigate the sensitivities on non-spinning and spinning PBHs arising from an EDGES-like measurement of the global 21 cm signal, and find that the sensitivities will be competitive with those arising from other astrophysical observables. We show that the sensitivities can be significantly strengthened depending on various uncertain astrophysical parameters. Besides, we also derive projections on the PBH density from the absorption trough expected during the Dark Ages. Our work shows that the near future unambiguous detection of the global 21 cm absorption troughs can be an excellent probe of PBH DM.