On The Vacuum Oscillation Solution of The Solar Neutrino Problem

We study the stability of the two--neutrino vacuum oscillation solution of the solar neutrino problem with respect to changes of the total fluxes of boron and beryllium neutrinos. For any value of $\Phi_{{\rm Be}}$ from the interval $0.7\Phi^{{\rm BP}}_{{\rm Be}}\leq \Phi_{{\rm Be}} \leq 1.3\Phi^{{\rm BP}}_{{\rm Be}}$ the solar $\nu_e$ oscillations into an active neutrino provide at 95\% C.L. a description of the existing solar neutrino data for $\Phi_{{\rm B}} \cong (0.35 - 3.4) \Phi^{{\rm BP}}_{{\rm B}}$, $\Phi^{{\rm BP}}_{{\rm B}}$ and $\Phi^{{\rm BP}}_{{\rm Be}}$ being the fluxes in the solar model of Bahcall--Pinsonneault from 1992. For $\Phi_{{\rm Be}}\cong (0.7 - 1.3)\Phi^{{\rm BP}}_{{\rm Be}}$ we find also at 95\% C.L. two new (one new) oscillation solutions for oscillations into active (sterile) neutrinos. The physical implications of the new solutions for the future solar neutrino experiments are discussed. The data rule out at 97\% -- 98\% (99 \%) C.L. the possibility of a universal (neutrino energy independent) suppression of the different components of the solar neutrino flux, resulting from solar $\nu_e$ oscillations or transitions into active (sterile) neutrino.