QCD condensate contributions to the effective quark potential in a covariant gauge - art. no. 114005

We discuss QCD condensate contributions to the gluon propagator both in the fixed-point gauge and in covariant gauges for the external QCD vacuum gluo n fields with the conclusion that a covariant gauge is essential to obtain a gauge-invariant QCD vacuum energy density difference and to retain the un itarity of the quark scattering amplitude. The gauge-invariant QCD condensa te contributions to the effective one-gluon exchange potential are evaluate d by using the effective gluon propagator, which produces a gauge-independe nt quark scattering amplitude. [S0556-2821(99)01321-1].