The 21 cm signal and the interplay between dark matter annihilations and
  astrophysical processes
  Future dedicated radio interferometers, including HERA and SKA, are very
promising tools that aim to study the epoch of reionization and beyond via
measurements of the 21 cm signal from neutral hydrogen. Dark matter (DM)
annihilations into charged particles change the thermal history of the Universe
and, as a consequence, affect the 21 cm signal. Accurately predicting the
effect of DM strongly relies on the modeling of annihilations inside halos. In
this work, we use up-to-date computations of the energy deposition rates by the
products from DM annihilations, a proper treatment of the contribution from DM
annihilations in halos, as well as values of the annihilation cross section
allowed by the most recent cosmological measurements from the Planck satellite.
Given current uncertainties on the description of the astrophysical processes
driving the epochs of reionization, X-ray heating and Lyman-$\alpha$ pumping,
we find that disentangling DM signatures from purely astrophysical effects,
related to early-time star formation processes or late-time galaxy X-ray
emissions, will be a challenging task. We conclude that only annihilations of
DM particles with masses of $\sim100$ MeV, could leave an unambiguous imprint
on the 21 cm signal and, in particular, on the 21 cm power spectrum. This is in
contrast to previous, more optimistic results in the literature, which have
claimed that strong signatures might also be present even for much higher DM
masses. Additional measurements of the 21 cm signal at different cosmic epochs
will be crucial in order to break the strong parameter degeneracies between DM
annihilations and astrophysical effects and undoubtedly single out a DM imprint
for masses different from $\sim100$ MeV.
