Neutrino anomalies and quasi dirac neutrinos

Abstract

We discuss the possibility of describing solar, atmospheric and LSND results with four neutrinos forming two quasidegenerate pairs. The simplest versions of this 2+2 scheme with either νe or νμmixing exclusively with sterile neutrino are disfavored by the SNO and atmospheric neutrino results, respectively. A generalized scheme with sterile state participating in both the solar and atmospheric oscillations is still allowed. We show that the complex pattern of mixing needed for this purpose follows from a simple L_e+L_μ−L_τ−L_s symmetry. The specific form of the L_e+L_μ−L_τ−L_ssymmetric mass matrix is determined from experimental results. Two theoretical schemes which lead to this form and a proper breaking of L_e+L_μ−L_τ−L_ssymmetry are discussed.