We study the imprint of dark matter ( DM ) annihilation on the global 21 cm signal from the Dark Ages to Cosmic Reionization .
Motivated by recent observations , we focus on three DM candidates : ( i ) a 10 GeV Bino-like neutralino ( ii ) a 200 GeV Wino and ( iii ) a 1 TeV heavier particle annihilating into leptons .
For each DM candidate we assume two values for the thermally averaged annihilation cross section \langle \sigma v \rangle , the standard thermal value \langle \sigma v \rangle _ { th } = 3 \times 10 ^ { -26 } \mbox { cm } ^ { 3 } \mbox { s } ^ { -1 } and the maximum value allowed by WMAP7 data , \langle \sigma v \rangle _ { max } .
We include the enhancement of DM annihilations due to collapsed structures , detailed estimates of energy deposition into the intergalactic medium ( IGM ) , as well realistic prescriptions for astrophysical sources of UV and X-ray radiation .
In these models , the additional heat input from DM annihilation suppresses the mean 21cm brightness temperature offset by \delta T _ { b } \sim few–100 mK .
In particular , the very deep \delta T _ { b } \sim - 150 mK absorption feature at \sim 20 \lower 2.15 pt \hbox { $ \buildrel < \over { \sim } $ } z \lower 2.15 pt \hbox { $ % \buildrel < \over { \sim } $ } 25 predicted by popular models of the first galaxies is considerably reduced or totally erased by some of the considered DM candidates .
Such an enhancement in IGM heating could come from either DM annihilations or a stronger-than-expected astrophysical component ( i.e .
abundant early X-ray sources ) .
However , we find that the two signatures are not degenerate , since the DM heating is dominated by halos several orders of magnitude smaller than those hosting galaxies , whose fractional abundance evolves more slowly resulting in a smaller gradient : d \delta T _ { b } / d \nu \lower 2.15 pt \hbox { $ \buildrel < \over { \sim } $ } 4 { mK } / { MHz } in the range \nu \sim 60 - 80 { MHz } .
The detection of such signals by future radio telescopes would be clear evidence of DM energy injection at high-redshifts .