Nontrivial center dominance in high temperature QCD

We investigate the properties of quarks and gluons above the chiral phase transition temperature T_c, using the renormalization group (RG) improved gauge action and the Wilson quark action with two degenerate quarks mainly on a 32^3×16 lattice. In the one-loop perturbation theory, the thermal ensemble is dominated by the gauge configurations with effectively Z(3) center twisted boundary conditions, making the thermal expectation value of the spatial Polyakov loop take a nontrivial Z(3) center. This is in agreement with our lattice simulation of high temperature quantum chromodynamics (QCD). We further observe that the temporal propagator of massless quarks at extremely high temperature β=100.0(T≃10^(58)T_c) remarkably agrees with the temporal propagator of free quarks with the Z(3) twisted boundary condition for t/L_t≥0.2, but differs from that with the Z(3) trivial boundary condition. As we increase the mass of quarks m_q, we find that the thermal ensemble continues to be dominated by the Z(3) twisted gauge field configurations as long as m_q ≤ 3.0T and above that the Z(3) trivial configurations come in. The transition is similar to what we found in the departure from the conformal region in the zero-temperature many-flavor conformal QCD on a finite lattice by increasing the mass of quarks