Three-generation neutrino mixing and LSND dark matter neutrinos

Abstract

The reported signal at the LSND experiment, when interpreted as neutrino mixing with $\delta m^2 = 6 \;\rm{eV}^2$, provides evidence for neutrinos with a cosmologically significant mass. However, attempts to reconcile this interpretation of the experiment with other hints about neutrino properties require a (sterile) fourth neutrino and/or an ``inverted'' neutrino mass hierarchy. An interpretation of the LSND experiment employing $\delta m^2 = 0.3\; \rm{eV}^2$, with three-generation mixing and a ``normal'' neutrino mass hierarchy, can just barely be reconciled with the negative results of other laboratory neutrino oscillation experiments and the positive hints of neutrino oscillation from the solar and atmospheric neutrino problems. Though subject to test by by future experiments, such a solution allows (but does not demand) neutrino masses relevant for dark matter.