Computation of the Vortex Free Energy in SU(2) Gauge Theory
  We present the first measurement of the vortex free-energy order parameter at weak coupling for SU(2) in simulations employing multihistogram methods. The result shows that the excitation probability for a sufficiently thick vortex in the vacuum tends to unity. This is rigorously known to provide a necessary and sufficient condition for maintaining confinement at weak coupling in SU(N) gauge theories. 
T.G. Kovacs (Leiden U.), and E.T. Tomboulis (UCLA)