MeV-Scale Dark Matter Deep Underground
  We demonstrate that current and planned underground neutrino experiments
could offer a powerful probe of few-MeV dark matter when combined with a nearby
high-intensity low-to-medium energy electron accelerator. This experimental
setup, an underground beam-dump experiment, is capable of decisively testing
the thermal freeze-out mechanism for several natural dark matter scenarios in
this mass range. We present the sensitivity reach in terms of the mass-coupling
parameter space of existing and planned detectors, such as Super-K, SNO+, and
JUNO, in conjunction with a hypothetical 100 MeV energy accelerator. This setup
can also greatly extend the sensitivity of direct searches for new light
weakly-coupled force-carriers independently of their connection to dark matter.
