On the vacuum oscillation solutions 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 B-8 and Be-7 neutrinos, Phi(B) and Phi(Be). For any values of Phi(Be) from the interval 0.7 Phi(Be)(BP) less than or equal to Phi(Be) less than or equal to 1.3 Phi(Be)(BP) the solar nu(e) oscillations into an active neutrino, nu(e) <----> nu(mu(tau)), provide at 95% C.L. a description of the existing solar neutrino data for Phi(B) congruent to (0.35-3.4) Phi(B)(BP), Phi(B)(BP) and Phi(Be)(BP) being the fluxes in the solar model of Bahcall and Pinsonneault from 1992. For Phi(Be) congruent to (0.7-1.3) Phi(Be)(BP) we find also at 95% C.L. two new [one new] nu(e) <----> nu(mu(tau),) [nu(e) <----> nu(s)] oscillation solutions: (i) for Phi(B) congruent to (0.35-0.43) Phi(B)(BP) at Delta m(2) congruent to (4.7-6.5) x 10(-12) eV(2) [(4.8-6.4) x 10(-12) eV(2)] and sin(2)2 theta greater than or similar to 0.7[10.74], and (ii) for Phi(B) congruent to (0.45-0.65)Phi(B)(BP) at Delta m(2) congruent to (3.2-4.0) x 10(-11) eV(2) and sin(2)2 theta <greather than or similar to> 0.59. The physical implications of the new solutions for the future solar neutrino experiments are discussed. The data rule out at 96%-98% [98.5%] 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.