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 mod els. We focus on a general class of four-neutrino models with two pairs of nearly degenerate mass eigenstates separated by approximately 1 eV, which c an describe the solar, atmospheric and LSND neutrino data. We present a gen eral parametrization of these models and discuss In detail the determinatio n of the mixing parameters and the mass matrix texture from current and fut ure neutrino data in the case where nu(e) and nu(mu) each mix primarily wit h one other neutrino. We find that measurable CP or T violation in long-bas eline experiments, with amplitude at the level of the LSND signal, is possi ble given current experimental constraints. Also, additional oscillation ef fects in short- and long-baseline experiments may be measurable in many cas es. We point put that, given separate scales for the mass-squared differenc es 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 whi ch 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 m odel. [S0556-2821(99)00313-6].