Thermal behavior of π-π scattering lengths in the Nambu-Jona-Lasinio model

We calculate the thermal evolution of π-π scattering lengths, in the framework 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 framework of different theoretical approaches.