Probing ultralight axions with the 21-cm signal during cosmic dawn

Ultralight axions (ULAs) are a promising and intriguing set of dark-matter candidates. We study the prospects to use forthcoming measurements of 21-cm fluctuations from cosmic dawn to probe ULAs. We focus in particular on the velocity acoustic oscillations (VAOs) in the large-scale 21-cm power spectrum, features imprinted by the long-wavelength (k & SIM; 0.1 Mpc-1) modulation, by dark-matter-baryon relative velocities, of the small-scale (k & SIM; 10 - 103 Mpc-1) power required to produce the stars that heat the neutral hydrogen. Damping of small-scale power by ULAs reduces the star-formation rate at cosmic dawn which then leads to a reduced VAO amplitude. Accounting for different assumptions for feedback and foregrounds, experiments like HERA may be sensitive to ULAs with masses up to m alpha & AP; 10-18 eV, two decades of mass higher than current constraints.

Automated summary

Studied the prospects of using forthcoming measurements of 21-cm fluctuations from cosmic dawn to probe ULAs, with a focus on VAOs in the large-scale 21-cm power spectrum.