Variations on four-neutrino oscillations

Abstract

We make a model-independent analysis of all available data that indicate neutrino oscillations. Using probability diagrams, we confirm that a mass spectrum with two nearly degenerate pairs of neutrinos separated by a mass gap of Ӎ1 eV is preferred over a spectrum with one mass eigenstate separated from the others. We derive some new relations among the four-neutrino mixing matrix elements. We design four-neutrino mass matrices with three active neutrinos and one sterile neutrino that naturally incorporate maximal oscillations of atmospheric and explain the solar neutrino and LSND results. The models allow either a large or small angle MSW or vacuum oscillation description of the solar neutrino deficit. The models predict ͑i͒ oscillations of either e → or e → s in long-baseline experiments at L/Eӷ1 km/GeV, with amplitude determined by the LSND oscillation amplitude and argument given by the atmospheric ␦m 2 , and ͑ii͒ the equality of the e disappearance probability, the disappearance probability, and the LSND → e appearance probability in short-baseline experiments. ͓S0556-2821͑98͒06921-5͔PACS number͑s͒: 14.60.Pq 4 He yield considerably weaker bounds ͓18͔. Another is that a small asymmetry (n Ϫn )/n ␥ տ7ϫ10 Ϫ5 of flavor neutrinos PHYSICAL REVIEW D, VOLUME 58, 093016

Large mixing and large hierarchy between neutrinos with abelian flavor symmetries

“…Outside our framework of supersymmetric Abelian horizontal symmetries there are, of course, many other proposals in the literature (some related to various symmetries and some which are simply ansatze for mass matrices) for achieving a large hierarchy together with large mixing [31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48].…”

Neutrino Mixing Schemes

“…The CHOOZ reactor experiment measuresν e survival, and is sensitive to oscillations betweenν e andν µ for δm 2 atm > 10 −3 eV 2 . The combined data from atmospheric experiments and CHOOZ favor sin θ 13 = 0 (i.e., pure ν µ → ν τ oscillations in the atmosphere) and suggest that sin θ 13 < 0.3 [24].…”

“…If we require both atmospheric and solar oscillations to be maximal, there is a unique three-neutrino solution to the neutrino mixing matrix [29]. This "bimaximal" mixing corresponds to θ 13 = 0 and |θ 12 | = |θ 23 | = π/4, and is a special case of the decoupled solution for atmospheric and solar neutrinos.…”

“…Further properties of the bimaximal and nearly bimaximal solutions and models that give rise to such solutions are discussed in Ref. [29].…”

Neutrino masses and mixings from an anomaly free SMG×U(1)2 model

“…In fact type III has previously been considered in the literature in [18], where the structure of the mass matrix is assumed to be due to a global L e − L µ − L τ symmetry. The fine-tuned case where B = A corresponds to the popular 'bi-maximal mixing' solution to the neutrino problems [19,20]. All of the textures (I, II, and III) examined here have previously been discussed in [21] by three of the authors of [18].…”