Abstract
The issue of the Becchi-Rouet-Stora-Tyutin (BRST) symmetry in the presence of the Gribov horizon is addressed in Euclidean Yang-Mills theories in the Landau gauge. The positivity of the Faddeev-Popov operator within the Gribov region enables us to convert the soft breaking of the BRST invariance exhibited by the Gribov-Zwanziger action into a nonlocal exact symmetry, displaying explicit dependence from the nonperturbative Gribov parameter. Despite its nonlocality, this symmetry turns out to be useful in order to establish nonperturbative Ward identities, allowing us to evaluate the vacuum expectation value of quantities which are BRST exact. These results are generalized to the refined Gribov-Zwanziger action introduced in Dudal et al. [Phys. Rev. D 77, 071501 (2008)], which yields a gluon propagator which is nonvanishing at the origin in momentum space, and a ghost propagator which is not enhanced in the infrared.
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