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We study the imprint of dark matter (DM) annihilation on the global 21 cmsignal from the Dark Ages to Cosmic Reionization. Motivated by recentobservations, we focus on three DM candidates: (i) a 10 GeV Bino-likeneutralino (ii) a 200 GeV Wino and (iii) a 1 TeV heavier particle annihilatinginto leptons. For each DM candidate we assume two values for the thermallyaveraged annihilation cross section \sigma v, the standard thermal value \sigmav_th = 3 x 10^-26 cm^3 s^-1 and the maximum value allowed by WMAP7 data, \sigmav_max. We include the enhancement of DM annihilations due to collapsedstructures, detailed estimates of energy deposition into the intergalacticmedium (IGM), as well realistic prescriptions for astrophysical sources of UVand X-ray radiation. In these models, the additional heat input from DMannihilation suppresses the mean 21cm brightness temperature offset by \deltaTb ~ few-100 mK. In particular, the very deep \delta Tb ~ -150 mK absorptionfeature at ~20 < z < 25 predicted by popular models of the first galaxies isconsiderably reduced or totally erased by some of the considered DM candidates.Such an enhancement in IGM heating could come from either DM annihilations or astronger-than-expected astrophysical component (i.e. abundant early X-raysources). However, we find that the two signatures are not degenerate, sincethe DM heating is dominated by halos several orders of magnitude smaller thanthose hosting galaxies, whose fractional abundance evolves more slowlyresulting in a smaller gradient: d \delta Tb/d \nu < 4 mK/MHz in the range \nu~60-80 MHz. The detection of such signals by future radio telescopes would beclear evidence of DM energy injection at high-redshifts.

The nature of dark matter from the global high redshift HI 21 cm signal