Covalent hadronic molecules induced by shared light quarks

Abstract

After examining Feynman diagrams corresponding to the , , , and hadronic molecular states, we propose a possible binding mechanism induced by shared light quarks. This mechanism is similar to the covalent bond in chemical molecules induced by shared electrons. We use the method of QCD sum rules to calculate its corresponding light-quark-exchange diagrams, and the obtained results indicate a model-independent hypothesis: the light-quark-exchange interaction is attractive when the shared light quarks are totally antisymmetric so they obey the Pauli principle. We build a toy model with four parameters to formulize this picture and estimate binding energies of some possibly-existing covalent hadronic molecules. A unique feature of this picture is that the binding energies of the (I)J P = (0)1+ hadronic molecules are much larger than those of the (I)J P = (0)1+ ones, while the (I)J P = (1/2)1/2+ hadronic molecules have similar binding energies.