Speaker
Description
The optimized perturbation theory (OPT), is implemented in the Nambu-Jonna--Lasinio (NJL) model with flavor symmetry $SU_{f}(3)$ to generate non-perturbative results beyond the large-$N_{c}$ approximation. Previous implementations of OPT, restricted to models with symmetry $SU_{f}(2)$, showed important repulsive vector contributions to the quark pressure stemming from Fock terms. These contributions are responsible for a better description of the lattice data in the regime of temperatures bellow the pseudo-critical temperature for the chiral transition $T_{c}$, but also create a maximum when $T \geq T_{c}$ in the second order coefficient of the Taylor series expansion of the pressure around zero chemical potential. It is shown how this maximum, not observed by the lattice simulations, is corrected in our implementation of the OPT in the NJL model, when the strange quark is considered. In this case, the vector repulsive Fock terms, are canceled by opposite sign counterparts. The validity of this OPT implementation is verified by the recovery of the usual results of the large-$N_{c}$ approximation in the limit $N_{c} \rightarrow \infty$ and also by observing that this method generates in a trivial way, the same results of the Hartree-Fock approximation.
