Model of four light neutrinos in the light of all present data

Abstract

Motivated by existing and recent data on possible neutrino oscillations, we propose a model of four light neutrinos (ν_e, ν_μ, ν_τ, and a singlet ν_S) with a pattern of masses and mixing derivable from a discrete Z₅ symmetry and the seesaw mechanism. Atmospheric neutrino oscillations occur between ν_μ and ν_τ as pseudo Dirac partners, whereas solar neutrino oscillations occur between ν_e and ν_S, a linear combination of which is massless. Additional oscillations may occur between ν_e and ν_μ to account for the recent observation of the LSND (Liquid Scintillator Neutrino Detector) experiment.