2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/211236We calculate the thermal evolution of $π-π$ scattering lengths, in the frame of the Nambu--Jona-Lasinio model. The thermal corrections were calculated at the one loop level using Thermofield Dynamics. We present also results for the pion thermal mass. Our procedure implies the modeling of a propagating scalar meson as a resumation of chains of quark bubbles, which is presented explicitly. We compare our results with previous analysis of this problem in the frame of different theoretical approaches.Revtex4, 6 pages, 5 figuresHigh Energy Physics - Phenomenologytext