Correlation functions are the building blocks in quantum field theory, from which any physical observable can be (in principle) calculated. In a theory with gauge symmetry, however, correlation functions are not physical objects themselves, being dependent on the particular gauge fixing prescription. A novel approach is presented, which allows to separately calculate, within the class of linear covariant gauges, the gauge dependent part of an arbitrary correlation function. This framework, which consists in introducing a Stueckelberg scalar field and other auxiliary fields in the theory, provides therefore a generalization of the Landau-Khalatnikov-Fradkin transformations, known in quantum electrodynamics, to the case of non abelian gauge symmetry.

Consistency checks have been carried out by calculating the gauge dependent part of the gluon propagator at the one loop level and of the quark propagator at the two loops level, in the massless case.The Stueckelberg formalism also allows accommodation of a dimension two gauge invariant composite operator that may be able to effectively capture non perturbative information through its renormalisation group flow. Preliminary results of its effect for the Yang-Mills propagators are presented.