Accessing the topological susceptibility via the Gribov horizon

The topological susceptibility,x(4), following the work of Witten and Veneziano, plays a key role in identifying the relative magnitude of the eta' mass, the so-called U(1)(A) problem. A nonzero x(4) is caused by the Veneziano ghost, the occurrence of an unphysical massless pole in the correlation function of the topological current K-mu. In this paper, we investigate the topological susceptibility, x(4), in SU(3) and SU(2) Euclidean Yang-Mills theory using an appropriate Pade approximation tool and a nonperturbative gluon propagator, within a Becchi-Rouet-Stora-Tyutin invariant framework and by taking into account Gribov copies in a general linear covariant gauge.