2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/40881The role of neutrinos in big bang nucleosynthesis is reviewed. Neutrino oscillations in the early universe both in resonance and non-resonance case are briefly discussed. BBN and supernova limits on heavy sterile neutrinos with the mass in 10-100 MeV range are presented and compared with direct experimental bounds.30 pages, 7 figures; talk at XV Rencontres de Physique de La Vallee d'Aoste, March, 2001High Energy Physics - Phenomenologytext