Speaker
Description
I will review several aspects of the QCD phase diagram, paying special attention to the interplay between chiral and $U(1)_A$ restoration, exploring partner degeneration and patterns of symmetry breaking. I will show that the use of Ward Identities (WI) allows to shed light on this issue, being also a fruitful tool for the understanding of thermal observables. In addition, effective chiral lagrangians provide a model-independent realization of these ideas. In fact, a simple meson gas description might be already a good approximation for certain observables. Thus, Chiral Perturbation Theory (ChPT) scattering amplitudes combined with unitarization generate a thermal $f_0(500)$ state which saturates the scalar susceptibility in accordance with the lattice. On the other hand, a $U(3)$ ChPT-based analysis of the topological susceptibility reveals interesting aspects of the role of the $\eta'$ state and the connection with chiral and $U_A(1)$ restoration through WI.
