The gluon propagator in linear covariant $R_\xi$ gauges

Explicit analytical expressions are derived for the gluon propagator in a generic linear covariant $R_\xi$ gauge, by a screened massive expansion for the exact Faddeev-Popov Lagrangian of pure Yang-Mills theory. At one-loop, if the gauge invariance of the pole structure is enforced, the gluon dressing function is entirely and uniquely determined, without any free parameter or external input. The gluon propagator is found finite in the IR for any $\xi$, with a slight decrease of its limit value when going from the Landau gauge ($\xi=0$) towards the Feynman gauge ($\xi=1$). An excellent agreement is found with the lattice in the range $0<\xi<0.5$ where the data are available.