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 $Z_5$ discrete 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.