A strong broadband 21 cm cosmological signal from dark matter spin-flip interactions

Understand

In the standard cosmology, it is believed that there are two relatively weak and distinct band-limited absorption features, with the first absorption minima near 20 MHz ($z\sim70$) and the other minima at higher frequencies between 50-110 MHz ($z\sim12-27$) in the global cosmological 21cm signal, which are signatures of collisional gas dynamics in the cosmic dark ages and Lyman-$\alpha$ photons from the first stars at cosmic dawn, respectively.

• A similar prediction of two distinct band-limited, but stronger, absorption features is expected in models with excess gas cooling, which have been invoked to explain the EDGES signal.
• In this work, we explore a novel mechanism, where dark matter spin-flip interactions with electrons through a light axial-vector mediator could directly induce a 21cm absorption signal which is characteristically different from either of these.
• We find generically, that our model predicts a strong, broadband absorption signal extending from frequencies as low as 1.4 MHz ($z\sim1000$), from early in the cosmic dark ages where no conventional signal is expected, all the way up to higher frequencies where star formation and X-ray heating effects are expected to terminate the absorption signal.