Thermodynamics in the Symmetry-Improved Cornwall–Jackiw–Tomboulis Formalism: Application to a Low-Energy Effective Theory of QCD

Understanding thermal phase transitions in quantum field theories often requires resummation techniques beyond ordinary perturbation theory. The Cornwall–Jackiw–Tomboulis (CJT) formalism provides a self-consistent framework for incorporating quantum fluctuations, with applications ranging from QCD to electroweak phase transitions. However, practical truncations can violate important symmetry constraints, motivating the symmetry-improved CJT formalism. In this talk, I will introduce the basic ideas behind these approaches and discuss the challenges of constructing consistent thermodynamic observables. As a concrete application, I will present our recent study of chiral thermodynamics in a three-flavor linear sigma model with quarks, focusing on the effects of different pressure prescriptions.