
The conformal symmetry of the QCD Lagrangian for massless quarks is broken both by renormalization effects and the gauge fixing procedure. Renormalized primitive divergent amplitudes have the property that their form away from the overall coincident point singularity is fully determined by the bare Lagrangian, and scale dependence is restricted to δfunctions at the singularity. If gauge fixing could be ignored, one would expect these amplitudes to be conformal invariant for noncoincident points. We find that the oneloop threegluon vertex function Γμνρ(x,y,z) is conformal invariant in this sense, if calculated in the background field formalism using the Feynman gauge for internal gluons. It is not yet clear why the expected breaking due to gauge fixing is absent. The conformal property implies that the gluon, ghost and quark loop contributions to Γμνρ are each purely numerical combinations of two universal conformal tensors Dμνρ(x,y,z) and Cμνρ(x,y,z) whose explicit form is given in the text. Only Dμνρ has an ultraviolet divergence, although Cμνρ requires a careful definition to resolve the expected ambiguity of a formally linearly divergent quantity. Regularization is straightforward and leads to a renormalized vertex function which satisfies the required Ward identity, and from which the betafunction is easily obtained. Exact conformal invariance is broken in higherloop orders, but we outline a speculative scenario in which the perturbative structure of the vertex function is determined from a conformal invariant primitive core by interplay of the renormalization group equation and Ward identities.
