Vacuum oscillation solution to the solar neutrino problem in standard and non-standard pictures

The neutrino long wavelength (just-so) oscillation is revisited as a solution to the solar neutrino problem. We consider just-so scenario in various cases: in the framework of the solar models with relaxed prediction of the boron neutrino flux, as well as in the presence of the non-standard weak range interactions between neutrino and matter constituents. We show that the fit of the experimental data in the just-so scenario is not very good for any reasonable value of the $^8B$ neutrino flux, but it substantially improves if the non-standard $\tau$-neutrino--electron interaction is included. These new interactions could also remove the conflict of the just-so picture with the shape of the SN 1987A neutrino spectrum. Special attention is devoted to the potential of the future real-time solar neutrino detectors as are Super-Kamiokande, SNO and BOREXINO, which could provide the model independent tests for the just-so scenario. In particular, these imply specific deformation of the original solar neutrino energy spectra, and time variation of the intermediate energy monochromatic neutrino ($^7Be$ and $pep$) signals.