engleski

When, and how much, is U_A(1) restored?

The U_A(1) symmetry breaking is tied to the dynamical chiral symmetry breaking through the QCD topological susceptibility expressed through quark-antiquark condensates. Therefore, the restoration of chiral symmetry at high temperatures T must lead to the restoration of U_A(1) symmetry at least partially, on the level of the η' mass. Condensates with explicit chiral symmetry breaking fall with T much more slowly than the massless quark-antiquark condensate. Then, in agreement with experiment, η does not exhibit any mass drop at all, while the significant drop of the η' mass signals only a partial restoration of U_A(1) symmetry, consuming only about a third of the U_A(1)- anomaly generated mass. For realistic explicit chiral symmetry breaking, there is an intermediate region between the chiral restoration at T=T_Ch and the η-η' anticrossing at T = 1.5 T_Ch which marks the effective U_A(1) restoration. There, the anomalous contributions to the masses become sufficiently weak, and η-η' complex enters the NS-S asymptotic regime of the vanishing U_A(1) anomaly influence.

QCD axial anomaly ; U_A(1) symmetry breaking ; dynamic and explicit chiral symmetry breaking ; symmetry restoration at high T

Link/poveznica znanstvenog skupa ACHT 2018: https://physikindico.uni-graz.at/event/1/