Probing New Physics at Cosmic Dawn with 21-cm Cosmology

The era of 21-cm cosmology has arrived, providing an exciting opportunity to probe new physics dynamics in the early universe. However, the information about new physics in this observable is obscured by astrophysical systematic uncertainties. Here, we show that the latter can be constrained by combining measurements of high redshift UV luminosity functions, the CMB optical depth to reionization, and the cosmic X-ray background. Leveraging those constraints, we demonstrate how new physics signatures can be disentangled from astrophysical effects. Focusing on the case in which a tiny millicharged subcomponent of dark matter cools the gas in the intergalactic medium, we find sharp predictions, with small uncertainties within the viable parameter space.