2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/48767We explore the extension of chiral perturbation theory out of thermal equilibrium. The pion decay constant becomes then a time-dependent function and we work within the Schwinger-Keldysh contour technique. A useful connection with curved space-time QFT allows to renormalise the model. We discuss the applicability of our approach within a relativistic heavy-ion collision environment.5 pages Latex, Proceedings of "Strong and Electroweak Matter 98", Nordita (Copenhaguen) 2-5 Dec.1998High Energy Physics - Phenomenologytext