Semiclassical treatment of matter-enhanced neutrino oscillations for an arbitrary density profile

The matter-enhanced oscillations of two neutrino flavors are studied using a uniform semiclassical approximation. Unlike some analytic studies which have focused on certain exactly-solvable densities, this method can be used for an arbitrary monotonic density profile. The method is applicable to a wider range of mixing parameters than previous approximate methods for arbitrary densities. The approximation is excellent in the adiabatic regime and up to the extreme nonadiabatic limit. In particular, the range of validity for this approximation extends farther into the nonadiabatic regime than for the linear Landau-Zener result. This method also allows calculation of the source- and detector-dependent terms in the unaveraged survival probability, and analytic results for these terms are given. These interference terms may be important in studying neutrino mixing in the sun or in supernovae.