Comments on Chern-Simons Contact Terms in Three Dimensions
  We study contact terms of conserved currents and the energy-momentum tensor in three-dimensional quantum field theory. They are associated with Chern-Simons terms for background fields. While the integer parts of these contact terms are ambiguous, their fractional parts are meaningful physical observables. In N=2 supersymmetric theories with a U(1)_R symmetry some of these observables lead to an anomaly. Moreover, they can be computed exactly using localization, leading to new tests of dualities. 
Cyril Closset, Thomas T. Dumitrescu, Guido Festuccia, Zohar   Komargodski, Nathan Seiberg
hep-th