The nilpotent "BRST" symmetry for the Gribov-Zwanziger theory

We have found a nilpotent quantum symmetry of Yang-Mills theory restricted to the Gribov region. In fact, we give a set of transformations for the filds a la BRST that leaves the Gribov-Zwanziger action invariant and obeys the nilpotency, although the usual BRST symmetry is broken due to the non-vanishing Gribov parameter representing the presence of the Gribov horizon in the configuration space of the Yang-Mills field. We show that the horizon condition (the gap equation determining the Gribov parameter) follows from the modified BRST invariance of the vacuum.