Probing the center-vortex area law in d=3: The role of inert vortices
  In center vortex theory, beyond the simplest picture of confinement several conceptual problems arise that are the subject of this paper. Confinement arises through averaging of phase factors which are gauge-group center elements raised to the power of the Gauss linking numbers of vortices. The simplest approach to confinement counts this link number by counting the number of vortices, considered in d=3 as infinitely-long closed self-avoiding random walks on a cubical lattice, piercing any surface spanning the Wilson loop. A given vortex, however, may pierce the spanning surface multiply with a link number smaller than the number of piercings. We call such vortices inert (although they may be only partially-inert). We estimate the dilution factor from inert vortices that reduces the ratio of fundamental string tension to vortex areal piercing density as roughly 0.6. Next we show how inert vortices resolve the old problem that the link number of a given vortex configuration is the same for any choice of spanning surface, yet only one such surface appears in the Wilson loop expectation value. Third, we discuss semi- quantitatively a configuration of two distinct Wilson loops separated by a variable distance, and show how inert vortices govern the transition between two allowed forms of the area law, one at small separation and one at large. The result is a finite-range Van der Waals force between the loops. Finally, in a problem related to the double-loop problem, we argue that inert vortices do not affect the fact that in the SU(3) baryonic area law, the mesonic string tension appears. 
John M. Cornwall