New constraints on neutrino oscillations in vacuum as a possible solution of the solar neutrino problem

Two-neutrino oscillations in vacuum are studied as a possible solution of the solar neutrino problem. New constraints on the parameter sin²2{θ}, characterizing the mixing of the electron neutrino with another active or sterile neutrino, as well as on the mass-squared difference {Δ}m² of their massive neutrino components, are derived using the latest results from the four solar neutrino experiments. Oscillations into a sterile neutrino are ruled out at 98% C.L. by the observed mean event rates even if one includes the uncertainties of the standard solar model predictions in the analysis.