2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/112490Neutrino dispersion properties in an active medium consisting of magnetic field and plasma are analysed. We consider in detail the contribution of a magnetic field into the neutrino self-energy operator Sigma (p). The results for this contribution were contradictory in the previous literature. For the conditions of the early universe where the background medium consists of a charge-symmetric plasma, the pure magnetic field contribution to the neutrino dispersion relation is proportional to (e B)^2 and thus comparable to the contribution of the magnetized plasma. We consider one more hypothetical effect of the active medium influence on neutrino properties, the so-called ``neutrino spin light'' discussed in the literature. We show that this effect has no physical region of realization because of the medium influence on photon dispersion.8 pages, LaTeX, no figures, based on the talk presented by A.V. Kuznetsov at the XIV International Seminar Quarks'2006, St.-Petersburg, Repino, Russia, May 19-25, 2006, to appear in the ProceedingsHigh Energy Physics - Phenomenologytext