U_A(1) Anomaly in Hot and Dense QCD and the Critical Surface

Understand

We discuss the chiral phase transition in hot and dense QCD with three light flavors.

• Inspired by the well known fact that the U_A(1) anomaly could induce first order phase transitions, we study the effect of the possible restoration of the U_A(1) symmetry at finite density.
• In particular, we explore the link between the U_A(1) restoration and the recent lattice QCD results of de Forcrand and Philipsen, in which the first order phase transition region near zero chemical potential (mu) shrinks in the quark mass and mu space when mu is increased.
• Starting from the Ginzburg-Landau theory for general discussions, we then use the Nambu--Jona-Lasinio model for quantitative studies.