Center-Vortex Solutions of the Yang-Mills Effective Action in Three and   Four Dimensions
  We calculate the one-loop effective action of the SU(2) Yang-Mills theory for center-vortex configurations, both in 3d and 4d. We find that in both cases there are minima of the effective action, corresponding to vortices of the transverse size approximately 4/g_3^2 and 1.7/Lambda_MS, respectively. The values of the effective actions at the minima are negative, suggesting that the Euclidian vacuum may be unstable with respect to creation of vortices. 
Dmitri Diakonov (Nordita & St. Petersburg, INP), Martin Maul (Lund U.)