XQCD 2018

The behaviour of a heavy quark within a hot QCD plasma is characterized by its kinetic and chemical equilibration rates, whereas the properties of a quark-antiquark pair are encoded in spectral functions related to various composite operators. We discuss the physics motivation, recent lattice studies, and outstanding challenges related to these observables.

Axial U(1) symmetry is broken by anomaly in QCD. In finite temperature, contribution to the order parameter of this symmetry from topologically non-trivial vacua may be suppressed and the symmetry could be effectively restored. This has been tested in lattice QCD simulations. But, the situation is still elusive. The fate of the axial U(1) symmetry is important in axion cosmology, universality...