2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/44985Primordial nucleosynthesis constrains the properties of light, stable neutrinos. Apart from the well--known limit on the number of neutrino species, there are also bounds on neutrino masses and magnetic moments. I discuss also sterile neutrinos and neutrino propagation in a primordial magnetic field, such as could be the origin of the observed galactic magnetic fields.16 pages, TEX, (2 figures available upon request). NORDITA-93/65 PHigh Energy Physics - Phenomenologytext