Signatures of pseudo-Dirac dark matter at high-intensity neutrino experiments

We (re) consider the sensitivity of past (LSND) and future (JSNS(2)) beam dump neutrino experiments to two models of MeV-scale pseudo-Dirac dark matter. Both LSND and JSNS(2) are close (24-30 m) to intense sources of light neutral mesons which may decay to dark matter via interactions involving a light mediator or dipole operators. The dark matter can then scatter or decay inside of the nearby detector. We show that the higher beam energy of JSNS(2) and resulting eta production can improve on the reach of LSND for light-mediator models with dark matter masses greater than m(pi)/2. Further, we find that both existing LSND and future JSNS(2) measurements can severely constrain the viable parameter space for a recently proposed model of dipole dark matter which could explain the 3.5 keV excess reported in observations of stacked galaxy clusters and the Galactic center.