Status of the Gribov-Pontecorvo solution to the solar neutrino problem

We discuss the status of the Gribov-Pontecorvo (GP) solution to the solar n eutrino problem. This solution naturally appears in bimaximal neutrino mixi ng, and reduces the solar and atmospheric neutrino problems to vacuum oscil lations of three active neutrinos. The GP solution predicts an energy-indep endent suppression of the solar neutrino flux. It is disfavoured by the rat e of the Homestake detector, but its statistical significance greatly impro ves, when the chlorine rate and the boron neutrino flux are slightly rescal ed, and when the Super-Kamiokande neutrino spectrum is included in the anal ysis. Our results show that rescaling of the chlorine signal by only 10% is sufficient for the GP solution to exist, if the boron-neutrino flux is tak en 10-20% lower than the SSM prediction. The regions allowed for the GP sol ution in the parameter space are found and observational signatures of this solution are discussed. (C) 2001 Elsevier Science B.V. All rights reserved .