Pseudo-Dirac neutrinos as a potential complete solution to the neutrino oscillation puzzle

Abstract

A solution for the neutrino mass and mixing pattern is proposed which is compatible with all available experimental data on neutrino oscillations. This solution involves Majorana neutrinos of the pseudo-Dirac type, i.e. m Majorana≪ m Dirac. The solar and atmospheric neutrino observations are mainly explained as ν e − ν e S and ν μ − ν μ S oscillations, where S indicates the sterile (“righthanded”) partner of each neutrino generation, while the LSND result is interpreted in terms of standard ν μ − ν e oscillations. The resulting constraints on ν μ − ν τ and ν τ − ν τ S oscillations are also discussed. This solution leaves room for a hierarchical mass and mixing scheme with a ν τ mass in the few eV range, as favoured by some dark matter scenarios. The apparent conflict with standard Big Bang nucleosynthesis is addressed and the implications for current and future experiments are discussed. It is argued that both short and long baseline accelerator neutrino experiments are needed in order to decide between this solution and other oscillation scenarios.