MATTER-INDUCED SPIN-FLAVOR NEUTRINO OSCILLATIONS AT FINITE TEMPERATURE AND DENSITY

We study the refraction of light Dirac neutrinos through a medium. In this connection, we extend a (vacuum) field theory electro-weak model. This model is designed to explain the solar neutrino problem and the neutrino flux anticorrelation effect associated with the sunspot activity, at finite temperature and density. The refractive index of the neutrino undergoing helicity flip in a hot and dense medium is then calculated in this framework. Some of the implications of these results in the early universe are discussed and compared with earlier works.