Fermionic vacuum structure of quantum chromodynamics with light dynamical quarks

We investigate lattice quantum chromodynamics (QCD) at finite temperature on a 4-dimensional space-time lattice with light dynamical quarks in the Kogut-Susskind formulation. In the presence of dynamical quarks the linear plus Coulomb potential between a static quark and a static antiquark of pure SU(3) gauge theory becomes screened due to the breaking of the gluonic string. In the hadronic phase the effects are more pronounced for light dynamical quarks. In the plasma phase of full QCD the influence of fermion loops is small. The fermionic vacuum around static quarks is investigated by correlating the local chiral condensate and the virtual charge density with Polyakov loops. The chiral condensate is suppressed in the vicinity of a static quark and this means that chiral symmetry is partially restored close to external charges. In the hadronic phase the local restoration of chiral symmetry strongly depends on the quark mass whereas in the plasma phase no mass dependence appears. We compare the lattice results with perturbation theory and with the Nambu-Jona-Lasinio model. We observe that a static quark polarizes the vacuum and attracts virtual antiquarks and repulses virtual quarks which leads to a net charge excess of opposite sign around static sources. At high temperatures the total induced charge around a static quark is much smaller than the induced charge in the hadronic phase at low temperatures. The numerical results are in agreement with a flux tube model