Canonical (anti-)commutation rules in QCD and unbroken gauge invariance,   QCD - the two central anomalies and canonical structure
  The regularities at large distances of complete gauge invariance in QCD are shown to bear nontrivial consequences for the selection among inequivalent representations of canonical commutation (anticommutation) rules for gauge boson (quark) fields. The trace anomaly forces a modification of the gauge boson Lagrangean and by this of the entire associated canonical structure. 
Peter Minkowski
hep-th