VARIATIONS ON 4-NEUTRINO OSCILLATIONS - ART. NO. 093016

We make a model-independent analysis of all available data that indica te neutrino oscillations. Using probability diagrams, we confirm that a mass spectrum with two nearly degenerate pairs of neutrinos separate d by a mass gap of similar or equal to 1 eV is preferred over a spectr um with one mass eigenstate separated from the others. We derive some new relations among the four-neutrino mixing matrix elements. We desig n four-neutrino mass matrices with three active neutrinos and one ster ile neutrino that naturally incorporate maximal oscillations of atmosp heric nu(mu) and explain the solar neutrino and LSND results. The mode ls allow either a large or small angle MSW or vacuum oscillation descr iption of the solar neutrino deficit. The models predict (1) oscillati ons of either nu(e) --> nu(tau) or nu(e) --> nu(s) in long-baseline ex periments at L/E much greater than 1 km/GeV, with amplitude determined by the LSND oscillation amplitude and argument given by the atmospher ic delta m(2), and (ii) the equality of the nu(e) disappearance probab ility, the nu(mu) disappearance probability, and the LSND nu(mu) --> n u(e) appearance probability in short-baseline experiments. [S0556-2821 (98)06921-5]