FLAVOR TRANSITIONS OF DIRAC-MAJORANA NEUTRINOS

From a phenomenological point of view, we study active-active and acti ve-sterile flavour-changing (and flavour-conserving) oscillations of D irac-Majorana neutrinos both in vacuum and ill matter. The general exp ressions for the transition probabilities in vacuum are reported. We t hen investigate some interesting consequences following from particula r simple forms of the neutrino mass matrices, and for the envisaged sc enarios we discuss in detail neutrino propagation in matter. Special e mphasis is given to the problem of occurrence of resonant enhancement of active-active a.nd active-sterile neutrino oscillations in a medium . The peculiar novel features related to the Dirac-Majorana nature of neutrinos are particularly pointed out.