A novel probe of the vacuum of the lattice gluodynamics
  We introduce a notion of minimal number of negative links on the lattice for a given original configuration of SU(2) fields. Negative links correspond to a large potential, not necessarily large action. The idea is that the minimal number of negative links is a gauge invariant notion. To check this hypothesis we measure correlator of two negative links, averaged over all the directions, as function of the distance between the links. The inverse correlation length coincides within the error bars with the lightest glueball mass. 
M. I. Polikarpov, S. N. Syritsyn and V. I. Zakharov