Exact results for supersymmetric abelian vortex loops in 2+1 dimensions
  We define a class of supersymmetric defect loop operators in N = 2 gauge theories in 2+1 dimensions. We give a prescription for computing the expectation value of such operators in a generic N = 2 theory on the three-sphere using localization. We elucidate the role of defect loop operators in IR dualities of supersymmetric gauge theories, and write down their transformation properties under the SL(2, Z) action on conformal theories with abelian global symmetries. 
Anton Kapustin, Brian Willett, and Itamar Yaakov
hep-th