On the symmetry improved CJT formalism in the $O(4)$ linear sigma model

Understand

By using the symmetry improved CJT effective formalism developed by Pilaftsis and Teresi, the chiral phase transition is reconsidered in the framework of the $O(4)$ linear sigma model in chiral limit.

• Our results confirm the restorations of the second-order phase transition and the Goldstone theorem in the Hartree approximation.
• Finally, we explicitly calculate the effective potentials via the order parameter for various temperatures and address advantages of the present method in comparison with the $O(N)$ model in large-$N$ approximation.