  Pure Yang-Mills SU(N) theory is studied in the Landau gauge and four
dimensional space. While leaving the original Lagrangian unmodified, a double
perturbative expansion is devised, based on a massive free-particle propagator.
In dimensional regularization, all diverging mass terms cancel exactly in the
double expansion, without the need to include mass counterterms that would
spoil the symmetry of the Lagrangian. No free parameters are included that were
not in the original theory, yielding a fully analytical approach from first
principles. The expansion is safe in the infrared and is equivalent to the
standard perturbation theory in the UV. At one-loop, explicit analytical
expressions are given for the propagators and the running coupling and are
found in excellent agreement with the data of lattice simulations. A universal
scaling property is predicted for the inverse propagators and shown to be
satisfied by the lattice data. Higher loops are found to be negligible in the
infrared below 300 MeV where the coupling becomes small and the one-loop
approximation is under full control.
