Instantons and the anomalous U(1)_A symmetry in high temperature QCD

I present a new way of understanding how chiral symmetry is realized in the high temperature phase of QCD. I show that a simple instanton model provides an excellent description of the lowest part of the spectrum of the Dirac operator, the part that dominates physical quantities related to chiral symmetry. Remarkably in a strongly interacting theory, this part of the spectrum can be understood in terms of a gas of non-interacting instantons. The model I present also indicates a possible way of resolving a long-standing debate about the fate of the anomalous U(1)_A symmetry at high temperature.