Hadronic Few-Body Systems in Chiral Dynamics

Abstract

Hadronic composite states are introduced as few-body systems in hadron physics. The Λ(1405) resonance is a good example of the hadronic few-body systems. It has turned out that Λ(1405) can be described by hadronic dynamics in a modern technology which incorporates coupled channel unitarity framework and chiral dynamics. The idea of the hadronicKN composite state of Λ(1405) is extended to kaonic few-body states. It is concluded that, due to the fact that K and N have similar interaction nature in s-waveK couplings, there are few-body quasibound states with kaons systematically just below the break-up thresholds, likeKN N ,KKN andKKK, as well as Λ(1405) as aKN quasibound state and f 0 (980) and a 0 (980) asKK.Keywords Hadronic composite state · Λ(1405) resonance · kaonic few-body systems · chiral dynamics 1 IntroductionHadrons are composite objects of quark and gluons governed by quantum chromodynamics, QCD. So far hundreds of hadrons have been experimentally observed in spite of only the five (or six) fundamental pieces, up, down, strange, charm, bottom (and top) quarks. The richness of hadron spectrum is a consequence of highly nontrivial dynamics of quarks and gluons confined in hadron. Precise measurement of hadron spectrum is one of the phenomenological ways to view colored dynamics of quarks and gluons inside hadron, and gives us clues of the confinement mechanism. Especially the systematics of energy excitation is a key issue to understand the hadron structure.A conventional picture of hadron is the quark model, in which one considers constituent quarks as quasi-particles moving in a one-body mean field created