Speaker
Description
The nature of chiral symmetry restoration and the identification of its correct pattern in terms of $O(4)$ and $U(1)_A$ symmetries are central problems for our present understanding of the QCD phase diagram, currently explored in lattice simulations and heavy-ion collisions. We will present a theoretical analysis based on Ward Identities for the full scalar/pseudoscalar $U(3)$ meson nonets, which sheds light on these issues. Our results lead to interesting conclusions regarding the behaviour of chiral partners in the limit of exact restoration and provide useful input for lattice analysis. In addition, it allows to connect partner degeneration with physical interaction vertices and to understand the temperature dependence of lattice screening masses in terms of quark condensate combinations. We will also describe the realization of these ideas in effective theories. In particular, a $U(3)$ Chiral Perturbation Theory calculation supports the partner and pattern conclusions from the WI analysis. The role of the thermal $f_0(500)$ state to describe the scalar susceptibility will also be analyzed, as well as the information provided by the large number of Goldstone Bosons framework.
