Neutrino mixing, CP and T violation, and textures in four-neutrino models -: art. no. 113010

We examine the prospects for determining the neutrino mixing matrix and for observing CP and T violation in neutrino oscillations in four-neutrino models. We focus on a general class of four-neutrino models with two pairs of nearly degenerate mass eigenstates separated by approximately 1 eV, which can describe the solar, atmospheric and LSND neutrino data. We present a general parametrization of these models and discuss In detail the determination of the mixing parameters and the mass matrix texture from current and future neutrino data in the case where nu(e) and nu(mu) each mix primarily with one other neutrino. We find that measurable CP or T violation in long-baseline experiments, with amplitude at the level of the LSND signal, is possible given current experimental constraints. Also, additional oscillation effects in short- and long-baseline experiments may be measurable in many cases. We point put that, given separate scales for the mass-squared differences of the solar and atmospheric oscillations, observable CP or T violation effects in neutrino oscillations signal the existence of a sterile neutrino. We examine several textures of the neutrino mass matrix and determine which textures can have measurable CP or T violation in neutrino oscillations in long-baseline experiments. We also briefly discuss some possible origins of the neutrino mass terms in straightforward extensions of the standard model. [S0556-2821(99)00313-6].