Solar neutrinos and 1-3 leptonic mixing

Effects of the 1-3 leptonic mixing on the solar neutrino observables are studied and the signatures of nonzero ₁₃ are identified. For this we have rederived the formula for 3-survival probability including all relevant corrections and constructed the isocontours of observables in the sin^2₁₂-sin^2₁₃ plane. Analysis of the solar neutrino data gives sin^2₁₃=0. 007-₀. ₀₀₇^+0. 080 (90% C. L. ) for m^2=810^-5 eV^2. The combination of the ratio CC/NC at Sudbury Neutrino Observatory (SNO) and gallium production rate selects sin^2₁₃=0. 0170. 026 (1). The global fit of all oscillation data leads to zero best value of sin^2₁₃. The sensitivity (1 error) of future solar neutrino studies to sin^2₁₃ can be improved down to 0. 01--0. 02 by precise measurements of the pp-neutrino flux and the CC/NC ratio as well as spectrum distortion at high (E>4 MeV) energies. Combination of experimental results sensitive to the low and high energy parts of the solar neutrino spectrum resolves the degeneracy of angles ₁₃ and ₁₂. Comparison of sin^2₁₃ as well as sin^2₁₂ measured in the solar neutrinos and in the reactor/accelerator experiments may reveal new effects which can not be seen otherwise.