Oscillations of pseudo Dirac neutrinos and the solar-neutrino problem.

Abstract

The oscillations of pseudo Dirac neutrinos in matter are discussed and applied to the solar-neutrino problem. Several scenarios such as both ${\ensuremath{\nu}}_{e}$ and ${\ensuremath{\nu}}_{\ensuremath{\mu}}$ being pseudo Dirac neutrinos and only ${\ensuremath{\nu}}_{e}$ or ${\ensuremath{\nu}}_{\ensuremath{\mu}}$ being a pseudo Dirac neutrino are examined. It is shown that the allowed region in the mass-mixing angle parameter space obtained by comparing the solar-neutrino data with the calculations based on the standard solar model and the Mikheyev-Smirnov-Wolfenstein effect is not unique. The results depend on the nature of neutrinos; for example, if both ${\ensuremath{\nu}}_{e}$ and ${\ensuremath{\nu}}_{\ensuremath{\mu}}$ are pseudo Dirac neutrinos, the allowed region determined by the current solar-neutrino data does not overlap with that obtained in the usual case of pure Dirac or Majorana neutrinos.