Edges and Endpoints in 21-cm Observations from Resonant Photon Production

We introduce a novel class of signatures---spectral edges and end points---in 21-cm measurements resulting from interactions between the standard dark sectors. Within context kinetically mixed photon, we demonstrate how resonant photon-to-photon conversions can imprint distinctive spectral features in observed brightness temperature, with implications for current, upcoming, proposed experiments targeting cosmic dawn ages. These signatures open up qualitatively new way to look physics beyond Standard Model using observations.