Abstract
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 ($\sim$10-80 MeV), carry a small charge ($\epsilon\sim 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 milli-charged DM makes up for $\sim$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.
Highlights
Stars are expected to have imprinted their evidence in the cosmic microwave background (CMB)
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
The recent results of EDGES suggest that the primordial gas underwent extensive cooling from some additional DM species
Summary
Stars are expected to have imprinted their evidence in the cosmic microwave background (CMB). The simplest possibility that has not been ruled out yet is that the DM interacts with lepton number Lμ − Lτ via either a scalar or vector mediator [10] This model is hard to constrain with lab experiments because DM does not interact with electrons, and especially for DM lighter than muons (as it is of main interest here), DM can annihilate only into muon and tau neutrinos. Νe and νe have been generated when the neutrinos reach the Earth, which makes it possible for detectors such as Super-Kamiokande (SK) [13] to detect them through charged-current interactions These neutrinos will show a very specific spectral feature; e.g., in the simplest model investigated in Ref.
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