OPE and quark-hadron duality for correlators of tetraquark currents in the 1/Nc expansion

We discuss the operator product expansion (OPE) and quark-hadron duality for two-point Green functions of tetraquark currents. We emphasize that the factorizable part of the OPE series for such Green functions is saturated by the full system of ordinary hadrons and therefore cannot have any relationship to the tetraquark bound states. Possible tetraquark bound states may be contained in nonfactorizable parts of these Green functions; in the framework of 1/Nc-expansion, nonfactorizable parts provide Nc-suppressed contributions compared to the Nc-leading factorizable parts. A possible exotic tetraquark state may appear only in Nc-subleading contributions to the QCD Green functions. This property provides constraints on the possible narrow tetraquark states at large-Nc.

Recording available at: https://mediaspace.epfl.ch/channel/High+Energy+Theory+Seminars/32518