The Non-Local Massive Yang-Mills Action as a Gauged Sigma Model
  We show that the massive Yang--Mills action having as a mass term the non-local operator introduced by Gubarov, Stodolsky, and Zakharov is classically equivalent to a principal gauged sigma model. The non-local mass corresponds to the topological term of the sigma model. The latter is obtained once the degrees of freedom implicitly generated in the non-local action are explicitly implemented as group elements. The non-local action is recovered by integrating out these group elements. In contrast to the usual gauge-fixed treatment, the sigma model point of view provides a safe framework in which calculation are tractable while keeping a full control of gauge-invariance. It shows that the non-local massive Yang--Mills action is naturally associated with the low-energy description of QCD in the Chiral Perturbation Theory approach. Moreover, the sigma model admits solutions called center vortices familiar in different (de)-confinement and chiral symmetry breaking scenarios. This suggests that the non-local operator introduced by Gubarov, Stodolsky, and Zakharov might be sensitive to center vortices configurations. 
Mboyo Esole