Adiabatic resonant oscillations of solar neutrinos in three generations

The Mikheyev-Smirnov-Wolfenstein model of resonant solar-neutrino oscillations is discussed for three generations of leptons. Assuming adiabatic transitions, bounds for the ..mu..- and e-neutrinos mass-squared difference ..delta../sub 21,0/ are obtained as a function of the e-..mu.. mixing angle theta/sub 1/. The allowed region in the ..delta../sub 21,0/-theta/sub 1/ plot that would solve the solar-neutrino problem is shown to be substantially larger than that of the two-generation case. In particular, the difference between the two- and three-generation cases becomes significant for theta/sub 1/ larger than --20/sup 0/.