Constraints on MeV dark matter using neutrino detectors and their implication for the 21-cm results

The recent results of the EDGES Collaboration indicate that during the era of reionization, the primordial gas was much colder than expected. The cooling of the gas could be explained by interactions between dark matter (DM) and particles in the primordial gas. Constraints from cosmology and particle experiments indicate that this DM should be light (∼10-80 MeV), carry a small charge (ϵ ∼ 10^-6-10^-4), and only make up a small fraction of the total amount of DM. Several constraints on the DM parameter space have already been made. We explore the yet unconstrained region in the case that the millicharged DM makes up ∼2% of the total dark matter, through the scenario in which this DM annihilates only into mu and tau neutrinos. We set upper limits on the annihilation cross section using the Super-Kamiokande data, and predict the limits that could be obtained through Hyper-Kamiokande, JUNO and DUNE. We find that data from Super-Kamiokande is not yet able to constrain this model, but future experiments might be. We furthermore explore DM annihilation into solely neutrinos in general, giving an update of the current limits, and predict the limits that could be placed with future experiments.