Exotic hadrons: Rich structure of multiparticle state near thresholds
Hadrons are a composite state of the elementary particles, quarks and gluons, bound by the strong interactions, which is one of the interesting phenomena in the low-energy QCD. In the ordinary hadron picture, baryons and mesons have been described as a three-quark state and quark-antiquark state, respectively. In fact, nucleons (protons and neutrons) can be understood as uud and udd baryons. However, accelerator experiments have reported unexpected states called exotic hadrons. Their natures cannot be understood by the ordinary hadron picture. In this talk, we study the hidden-charm pentaquarks Pc and Pcs reported by the LHCb experiment recently. We have considered the hybrid model introducing the mixture of the hadronic molecule and compact multiquark state to study the pentaquark's energy spectra. We also discuss the role of the interactions in resonances obtained in this study.