Strong new limits on light dark matter from neutrino experiments

The nondetection of GeV-scale weakly interacting massive particles (WIMPs) has led to increased interest in more general candidates, including sub-GeV dark matter. Direct-detection experiments, despite their high sensitivity to WIMPs, are largely blind to sub-GeV dark matter. Recent work has shown that cosmic-ray elastic scattering with sub-GeV dark matter would both alter the observed cosmic ray spectra and produce a flux of relativistic dark matter, which would be detectable with traditional dark matter experiments as well as larger, higher-threshold detectors for neutrinos. Using data, detectors, and analysis techniques not previously considered, we substantially increase the regions of parameter space excluded by neutrino experiments for both dark matter--nucleon and dark matter--electron elastic scattering. We also show how to further improve sensitivity to light dark matter.