OSCILLATIONS OF PSEUDO-DIRAC NEUTRINOS AND THE SOLAR-NEUTRINO PROBLEM

The oscillations of pseudo Dirac neutrinos in matter are discussed and applied to the solar-neutrino problem. Several scenarios such as both nu(e) and nu(mu) being pseudo Dirac neutrinos and only nu(e) or nu(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 v(e) and v(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.