2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/49921Using the ideas of effective field theory and dimensional reduction, we relate the parameters of two low energy models of QCD: the O(N) nonlinear sigma model in D=3+1, which describes the dynamics of cool pions, and the O(N) Heisenberg magnet in D=3+0, which is commonly argued to reproduce the correct critical behaviour of the chiral phase transition. As a result, we obtain a generalized expression for the finite temperature pion decay constant which reproduces, in certain limits, the available expressions in the literature.RevTex, 3 pages, no figuresHigh Energy Physics - Theorytext