Analytical description of quasivacuum oscillations of solar neutrinos

We propose a simple prescription to calculate the solar neutrino survival probability P-ee in the quasivacuum oscillation (QVO) regime. Such a prescription is obtained by matching perturbative and exact analytical results, which effectively take into account the density distribution in the Sun as provided by the standard solar model. The resulting analytical recipe for the calculation of P-ee is shown to reach its highest accuracy (\DeltaP(ee)\less than or equal to2.6 x 10(-2) in the whole QVO range) when the familiar prescription of choosing the solar density scale parameter r(0) at the Mikheyev-Smirnov-Wolfenstein (MSW) resonance point is replaced by a new one, namely, when, r(0) is chosen at the point of maximal violation of adiabaticity (MVA) along the neutrino trajectory in the Sun. The MVA prescription admits a smooth transition from the QVO regime to the MSW transition one. We discuss in detail the phase acquired by neutrinos in the Sun, and show that it might be of relevance for the studies of relatively short time scale variations of the fluxes of the solar nu lines in the future real-time solar neutrino experiments. Finally, we elucidate the role of matter effects in the convective zone of the Sun.