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 θ₁₃ are identified. For this we have rederived the formula for 3ν-survival probability including all relevant corrections and constructed the isocontours of observables in the sin²θ₁₂-sin²θ₁₃ plane. Analysis of the solar neutrino data gives sin²θ₁₃=0.007_-0.007+0.080 (90% C.L.) for Δm²=8×10^-5 eV². The combination of the ratio CC/NC at Sudbury Neutrino Observatory (SNO) and gallium production rate selects sin²θ₁₃=0.017±0.026 (1σ). The global fit of all oscillation data leads to zero best value of sin²θ₁₃. The sensitivity (1σ error) of future solar neutrino studies to sin²θ₁₃ 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 θ₁₃ and θ₁₂. Comparison of sin²θ₁₃ as well as sin²θ₁₂ measured in the solar neutrinos and in the reactor/accelerator experiments may reveal new effects which can not be seen otherwise.