NEUTRINO PROPAGATION IN A MEDIUM WITH A MAGNETIC-FIELD

We study the properties of neutrinos propagating in an isotropic magne tized medium in the two physical approximations of degenerate Fermi ga s and classical plasma. The dispersion relation shows that, for peculi ar configurations of the magnetic field, neutrinos can propagate freel y as in vacuum, also for very large density; this result can be very i mportant in the study of supernova evolution. For mixed neutrinos, the presence of a magnetic field can alter significatively MSW oscillatio ns, and for particular configurations of the field the resonance condi tion no longer occurs. Furthermore, on the contrary to that happens in non-magnetized media, spatial dispersion arises and neutrino trajecto ry can be in principle deviated; however a simple estimate shows that this deviation is not detectable.