Sub-MeV self-interacting dark matter

Cosmological models with cold dark matter composed of weakly interacting particles predict overly dense cores in the centers of galaxies and clusters and an overly large number of halos within the Local Group compared to actual observations. We propose that the conflict can be resolved if the cold dark matter particles are self-interacting with a large scattering cross-section but negligible annihilation or dissipation. In this scenario, astronomical observations may enable us to study dark matter properties that are inaccessible in the laboratory

A search for muon anti-neutrino to electron anti-neutrino oscillations was conducted by the Liquid Scintillator Neutrino Detector at the Los Alamos Neutron Science Center using muon anti-neutrinos from positive muon decay at rest. A total excess of 87.9 +/- 22.4 +/- 6.0 events consistent with electron anti-neutrino plus proton scattering to positron plus neutron was observed above the expected background. This excess corresponds to an oscillation probability of (0.264 +/- 0.067 +/- 0.045), which is consistent with an earlier analysis. In conjunction with other known limits on neutrino oscillations, the LSND data suggest that neutrino oscillations occur in the 0.2-10 eV^2/c^4 Delta-m^2 range, indicating a neutrino mass greater than 0.4 eV/c^2.