Vacuum condensate of mass dimension 2 as the origin of mass gap and quark confinement

We propose a vacuum condensate of mass dimension 2 consisting of gluons and ghosts in the framework of the manifestly covariant gauge fixing of the SU(N) Yang-Mills theory. This quantity is both BRST and anti-BRST invariant for any gauge. It includes the ghost condensation $C^a \bar{C}^a$ proposed first in the modified Maximal Abelian gauge and reduces to the gluon condensates $(\mathscr{A}_\mu)^2$ of mass dimension 2 proposed recently in the Landau gauge of the Lorentz gauge fixing. The vacuum condensate of dimensions 2 can provide the effective mass for gluons and ghosts. The possible existence of such condensations is demonstrated by calculating the operator product expansion of the gluon and ghost propagators in both gauges. Its implications to quark confinement are also discussed in consistent with the previous works.