VIOLATIONS OF LOCAL DUALITY IN THE HEAVY-QUARK SECTOR

We examine the origin of possible failures of the quark-hadron local d uality. In particular, we consider a correlator of two currents compri sing heavy quark operators, and compare the evaluation by the Operator Product Expansion with the result obtained inserting an infinite set of hadronic states, in the N-c --> infinity limit. Whereas the smeared spectral functions agree with each other, their local behaviour is di fferent. The difference manifests itself in the form of a term O(Lambd a/epsilon) (epsilon being the residual energy) that is not present in the expansion in powers of Lambda/epsilon predicted by the OPE. (C) 19 97 Elsevier Science B.V.