Two-loop contribution of quarks to the condensate of the gluon field at finite temperatures

The two-loop contribution of quarks to the effective potential V(A0, ξ) for the gluon field Aaμ = δμ0(δa3A30 + δa8A80) = const is calculated within the framework of finite-temperature QCD. Calculations are carried out in an arbitrary relativistic background gauge Rextξ. With allowance made for the contribution of gluons, calculated earlier, it is found that the global minimum of the potential corresponds to A0 = 0 and does not depend on the number of flavors of quarks. The dependence of the magnitude of the condensate on the gauge is discussed. It is shown that the effective potential satisfies the Nielsen identity. Along with the result A0 = 0, this implies that A0-condensation is gauge invariant. A change in the symmetry of vacuum caused by the effect of quarks is studied. 12 refs., 2 figs