2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/46255At nonzero temperature, pions propagate through a thermal medium at less than the speed of light. About low temperature, this effect begins not at $\sim T^2$, but at next to leading order, $\sim T^4$. We also derive the generalization of the relation of Gell-Mann, Oakes, and Renner to nonzero temperature.11 pages, latex + sprocl.sty, talk given at Continuous Advances in QCD'96, MinneapolisHigh Energy Physics - Phenomenologytext