Bounds on Dark-Matter Annihilations from 21-cm Data

The observation of an absorption feature in the 21-cm spectrum at redshift z approximate to 17 implies bounds on dark-matter (DM) annihilations for a broad range of masses, given that significant heating of the intergalactic medium would have erased such a feature. The resulting bounds on the DM annihilation cross sections are comparable to the strongest ones from all other observables.