Status of the solution to the solar neutrino problem based on nonstandard neutrino interactions

We analyze the current status of the solution to the solar neutrino problem based both on (a) nonstandard flavor-changing neutrino interactions (FCNI) and (b) nonuniversal flavor diagonal neutrino interactions (FDNI). We find that FCNI and FDNI with matter in the Sun as well as in the Earth provide a good fit not only to the total rate measured by all solar neutrino experiments but also to the day-night and seasonal variations of the event rate, as well as the recoil electron energy spectrum measured by the SuperKamiokande Collaboration. This solution does not require massive neutrinos and neutrino mixing in vacuum. Stringent experimental constraints on FCNI from bounds on lepton flavor violating decays and on FDNI from limits on lepton universality violation rule out ${\nu }_e\to {\nu }_{\mu }$ transitions induced by new physics as a solution to the solar neutrino problem. However, a solution involving ${\nu }_e\to {\nu }_{\tau }$ transitions is viable and could be tested independently by the upcoming B factories if flavor violating tau decays would be observed at a rate close to the present upper bounds.