Quantum, higher-spin, local charges in symmetric space sigma models

Potential anomalies are analysed for the local spin-3 and spin-4 classically conserved currents in any two-dimensional sigma model on a compact symmetric space G/H, with G and H classical groups. Quantum local conserved charges are shown to exist in exactly those models which also possess quantum non-local (yangian) charges. The possibility of larger sets of quantum local charges is discussed and shown to be consistent with known S-matrix results and the behaviour of the corresponding yangian representations