Optimized perturbation theory applied to the nonlinear sigma model

Gabriel Neves Ferrari

In this work, we study the nonlinear sigma model (NLSM), an effective model for the quantum chromodynamics (QCD). Although this model describes partially the strong interaction, it does not contain fermions, and due to this gluonic character the NLSM has some common features with Yang-Mills theories such as trace anomaly, a nonperturbative generation of a mass gap and asymptotic freedom. Here we show preliminary results for the application of the Optimized Perturbation Theory (OPT) to the NLSM, in order to analyze how thermodynamic quantitites such as pressure and trace anomaly behave when one goes beyond the mean-field approximation (MFA) in this way.