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 ⁸B and ⁷Be neutrinos, ΦB and ΦBe. For any value of ΦBe from the interval 0.7ΦBeBP{≤}ΦBe{≤}1.3ΦBeBP the solar νₑ oscillations into an active neutrino, νₑ{}ν_μ(τ), provide at 95% C.L. a description of the existing solar neutrino data for ΦB{}(0.35--3.4)ΦBBP, ΦBBP and ΦBeBP being the fluxes in the solar model of Bahcall and Pinsonneault from 1992. For ΦBe{}(0.7--1.3)ΦBeBP we find also at 95% C.L. two new [one new] νₑ{}ν_μ(τ) [νₑ{}νₛ] oscillation solutions: (i) for ΦB{}(0.35--0.43)ΦBBP at {Δ}m²{}(4.7--6.5)×{}10^-12 eV² [(4.8--6.4)×{}10^-12 eV²] and sin²2{θ}{}0.71[0.74], and (ii) for ΦB{}(0.45--0.65)ΦBBP at {Δ}m²{}(3.2--4.0)×{}10^-11 eV² and sin²2{θ}{}0.59.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 νₑ oscillations or transitions into active (sterile) neutrino. {} 1996 The American Physical Society.