2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/47134We expose briefly the role of entropy in the early universe and in particular the importance of searching for new mechanisms of entropy production. We describe a mechanism that shows how entropy is produced during early annihilations and under which conditions the production is not negligible. A MeV tau neutrino provides an interesting application.9 pages, Latex, 3 ps-figures included. Talk presented in the Nato School Sesion "Generation of Cosmological Large-Scale Structure" (Erice, November 1996)High Energy Physics - PhenomenologyAstrophysicstext