An exact analytic description of neutrino oscillations in matter with exponentially varying density for arbitrary number of neutrino species

Exact analytical expressions in terms of generalized confluent hypergeometric functions for the transition amplitudes of neutrino oscillations in presence of matter are computed for an arbitrary number of species. The density of matter is assumed to be exponentially decaying. The results can be used for the description of matter-induced neutrino oscillations in the Sun which can take place when the solar neutrinos prop-agate radially from the interior to the surface. Expressions are particularly simple in the limit of infinite propagation time as is suitable for the case of detection at Earth.