In this work, we study the elastic scattering of pions at finite temperature using a O(N+1)/O(N)-invariant nonlinear sigma model as an approach to Chiral Perturbation Theory. This model takes, instead of the well-known momentum expansion, a set of N+1 pseudoscalar particles, whose perturbative parameter is 1/N. Since strangeness is not considered, the model is fully simplified and allows us to write amplitudes in a very easy way, as we will show here.
