Could the 21-cm absorption be explained by the dark matter suggested by 8 Be transitions?

Abstract

The stronger than expected 21-cm absorption was observed by EDGES recently, and another anomaly of 8Be transitions would be signatures of new interactions. These two issues may be related to each other, e.g., pseudoscalar A mediated fermionic millicharged dark matter (DM) and the 21-cm absorption could be induced by photon mediated scattering between MeV millicharged DM and hydrogen. This will be explored in this paper. For fermionic millicharged DM χ¯ χ with masses in a range of 2 mA< 2 mχ< 3 mA, the p-wave annihilation χ¯ χ→ AA would be dominant during DM freeze-out. The s-wave annihilation χ¯ χ→ A, γ→ e+e- is tolerant by constraints from CMB and the 21-cm absorption. The millicharged DM can evade constraints from direct detection experiments. The process of K+→ π+π0 with the invisible decay π0→ χ¯ χ could be employed to search for the millicharged DM, and future high intensity K+ sources, such as NA62, will do the job.