High-energy neutrino oscillations in absorbing matter

The impact of neutrino mixing, refraction and absorption on high-energy neutrino propagation through a thick medium is studied using the MSW evolution equation with complex indices of refraction. It is found that, owing to the mixing with sterile neutrinos, the penetrability of active neutrinos may be many orders of magnitude larger than it would be in the absence of mixing. The effect is highly sensitive to changes in density and composition of the matter background as well as to neutrino energy and mixing parameters. This may lead to observational consequences in neutrino astrophysics.