MATTER-ENHANCED 3-FLAVOR OSCILLATIONS AND THE SOLAR-NEUTRINO PROBLEM

We present a systematic analysis of the three-flavor Mikheyev-Smirnov- Wolfenstein (MSW) oscillation solutions to the solar neutrino problem, in the hypothesis that the two independent neutrino square mass diffe rences, delta m(2) and m(2), are well separated: delta m(2) much less than m(2). At zeroth order in delta m(2)/m(2), the relevant variables for solar neutrinos are delta m(2) and two mixing angles omega and phi . We introduce new graphical representations of the parameter space (d elta m(2),omega,phi) that prove useful both to analyze the properties of the electron-neutrino survival probability and to present the resul ts of the analysis of solar neutrino data. We make a detailed comparis on between the theoretical predictions of the Bahcall-Pinsonneault sta ndard solar model and the current experimental results on solar neutri no rates, and discuss thoroughly the MSW solutions found by spanning t he whole three-flavor space (delta m(2), omega, phi). The allowed regi ons can be radically different from the usual ''small mixing'' and ''l arge mixing'' solutions, characteristic of the usual two-generation MS W approach. We also discuss the link between these results and the ind ependent information on neutrino masses and mixings coming from accele rator and reactor oscillation searches.