On Quark-Hadron Duality in the Heavy Quark Sector

I discuss the issue of quark-hadron duality in the system of heavy-light quark mesons. As an example, I consider a correlator of two currents comprising heavy quark operators, and I compare the OPE expression with the result obtained by a complete insertion of hadronic states. After a smearing procedure, OPE and hadronic spectral functions agree with each other. However, the local behaviour of the two functions is different, and the difference manifests itself in a term which is absent in the OPE.