  Physical quantities in gauge theories have to be gauge-independent. However
their evaluation can be greatly simplified by working in particular gauges.
Since physical quantities have to be gauge invariant, it is important to
establish an approach allowing the comparison of computations carried out in
different gauges even beyond perturbation theory. We show that the dependence
on the gauge parameter $\alpha=0$ in Yang-Mills theories is controlled by a
canonical flow that explicitly solves the Nielsen identities of the model.
Green's functions in the $\alpha=0$ gauge are given by amplitudes evaluated in
the theory at $\alpha=0$ (e.g., in the example of Lorentz-covariant gauges, in
terms of Landau gauge amplitudes) plus some contributions induced by the
$\alpha=0$-dependence of the generating functional of the canonical flow.
Explicit formulas are presented and an application of the formalism to the
gluon propagator is discussed.

High Energy Physics - Phenomenology;High Energy Physics - Theory