Neutrino oscillations in a variable-density medium and $\nu -$ bursts due to the gravitational collapse of stars

Abstract

Under certain conditions, the propagation of a beam of oscillating neutrinos in a variable-density medium takes the form of an almost complete transformation of the initial type of neutrino into another type. The depth of oscillations is then negligible. The transformation can occur in the cores and envelopes of collapsing stars.

Comments: latex, 5 pages, 2 figures, comments (June 2007) added