Hidden MeV-Scale Dark Matter in Neutrino Detectors

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The possibility of direct detection of light fermionic dark matter in neutrino detectors is explored from a model-independent standpoint. We consider all operators of dimension six or lower which can contribute to the interaction f p → e+ n, where f is a dark Majorana or Dirac fermion. Constraints on these operators are then obtained from the f lifetime and its decays which produce visible γ rays or electrons. We find one operator which would allow f p → e+ n at interesting rates in neutrino detectors, as long as mf mπ. The existing constraints on light dark matter from relic density arguments, supernova cooling rates, and big-bang nucleosynthesis are then reviewed. We calculate the cross-section for f p → e+ n in neutrino detectors implied by this operator, and find that Super-K can probe the new physics scale Λ for this interaction up to O(100 TeV)