Nonlocal color interactions in a gauge-invariant formulation of QCD
  We construct a set of states that implement the non-Abelian Gauss's law for QCD. We also construct a set of gauge-invariant operator-valued quark and gluon fields by establishing an explicit unitary equivalence between the Gauss's law operator and the `pure glue' part of the Gauss's law operator. This unitary equivalence enables us to use the `pure glue' Gauss's law operator to represent the entire Gauss's law operator in a new representation. Since the quark field commutes with the `pure glue' Gauss's law operator, it is a gauge-invariant field in this new representation. We use the unitary equivalence of the new and the conventional representations to construct gauge-invariant quark and gluon fields in both representations, and to transform the QCD Hamiltonian in the temporal gauge so that it is expressed entirely in terms of gauge-invariant quantities. In that form, all interactions between quark fields mediated by `pure gauge' components of the gluon field have been transformed away, and replaced by a nonlocal interaction between gauge-invariant color-charge densities. This feature --- that, in gauge-invariant formulations, interactions mediated by pure gauge components of gauge fields have been replaced by nonlocal interactions --- is shared by many gauge theories. In QED, the resulting nonlocal interaction is the Coulomb interaction, which is the Abelian analog of the QCD interaction we have identified and are describing in this work. The leading term, in a multipole expansion, of this nonlocal QCD interaction vanishes for quarks in color-singlet configurations, suggesting a dynamical origin for color confinement; higher order terms of this multipole expansion suggest a QCD mechanism for color transparency. We also show how, in an SU(2) model, this nonlocal interaction can be evaluated nonperturbatively. 
Kurt Haller and Lusheng Chen