Infrared massive gluon propagator from a BRST-invariant Gribov horizon in a family of covariant gauges

Abstract: A distinctive feature observed in lattice simulations of confining nonabelian gauge theories, such as Quantum Chromodynamics, is the presence of a dynamical mass for the gauge field in the low energy regime of the theory. In the Gribov-Zwanziger framework in the Landau gauge, such mass is a consequence of the generation of the dimension two condensates $\langle A_\mu^aA_\mu^a\rangle$ and $\langle \bar\varphi_\mu^{ab}\varphi_\mu^{ab}-\bar\omega_\mu^{ab}\omega_\mu^{ab}\rangle$, where $A$ is the gluon field and the fields $\bar\varphi$, $\varphi$, $\bar\omega$, and $\omega$ are Zwanziger's auxiliary fields. In this work, we show that, in the recently developed BRST-invariant version of the Refined Gribov-Zwanziger theory, these condensates can be introduced in a BRST-invariant way for a family of $R_\xi$ gauges. Their values are explicitly computed to first order and turn out to be independent of the gauge parameters contained in the gauge-fixing condition, as expected from the BRST invariance of the formulation. This fact supports the possibility of a gauge-parameter independent nonzero infrared gluon mass, whose value is the same as the one in the Landau gauge.