EXOTIC SOLUTIONS TO THE SOLAR NEUTRINO PROBLEM AND SOME IMPLICATIONS FOR LOW ENERGY SOLAR NEUTRINO EXPERIMENTS a

It is considered that observed data coming from atmospheric neutrino experiments 1 are compelling evidence of neutrino oscillation indicating the presence of neutrino mass and flavor mixing . This is now being confirmed by the ongoing K2K experiment . Results of the solar neutrino experiments 5 are also supporting such mass induced neutrino oscillations hypothesis, either through the matter enhanced MSW mechanism or through the vacuum oscillation. I will call these explanations “standard solutions” to the solar neutrino problem (SNP) as they are based only on neutrino mass and flavor mixing, the most natural extension of the standard model. Althogh not yet confirmed by other experiment, the LSND data 7 are also indicating neutrino mass and mixing. On the other hand, several alternative scenarios, which can explain these observations without invoking neutrino mass and/or flavor mixing, have been proposed and some of them are not yet excluded. I will call them “non-standard” or “exotic” solutions, as they are theoretically less motivated compared to the standard solutions. In this talk, from the phenomenological point of view, I will review such non-standard solutions to the SNP which are provided by the neutrino conversion induced by resonant spin-flavor precession (RSFP) , non-standard neutrino interactions (NSNI) , and violation of the equivalence principle (VEP) 13 and show that they can provide a good fit to the solar neutrino data. In the end, I will try to consider some possible implications for low energy solar neutrino experiments. For non-standard explanations of the atmospheric neutrino observations, see Ref. 14 for a review.