Measuring the cosmic expansion rate using 21-cm velocity acoustic oscillations

The fluctuations in the dark matter-baryon relative velocity field are imprinted as acoustic oscillations in the 21-cm power spectrum during cosmic dawn (CD). These velocity acoustic oscillations (VAOs) keep the imprints of the comoving sound horizon scale. In a previous work by Muñoz, it has been demonstrated that these VAOs can be treated as standard rulers to measure the cosmic expansion rate at high redshifts by considering a variety of Lyman-Werner feedback strengths and foreground contamination scenarios. Here we extend that analysis by using a modified version of the public code 21cmfast. We use this code to simulate the VAOs in 21-cm power spectrum and forecast the potential to constrain H(z) with the HERA radio telescope, taking into account the effects of Lyman-α heating, Lyman-Werner feedback and foregrounds, the dependence on various astrophysical parameters, and the degeneracy with cosmological parameters. We find that H(z) can be measured with HERA at ∼0.3-6% relative accuracy in the range 11<z<20, under different astrophysical and foreground scenarios, with uncertainties in the Planck cosmological parameters setting a ∼0.08-0.2% relative-error floor in the measurement. This accuracy is on par with most low-redshift measurements and can be helpful in testing various cosmological scenarios motivated by the ongoing "Hubble tension."