The nature of the resonance in chiral dynamics

The Λ ( 1405 ) baryon resonance plays an outstanding role in various aspects in hadron and nuclear physics. It has been considered that the Λ ( 1405 ) resonance is generated by the attractive interaction of the antikaon and the nucleon as a quasi-bound state below its threshold decaying into the π Σ channel. Thus, the structure of Λ ( 1405 ) is closely related to the K ̄ N interaction which is the fundamental ingredient to study few-body systems with antikaon. In this paper, after reviewing the basic properties of the Λ ( 1405 ) resonance, we introduce the dynamical coupled-channel model which respects chiral symmetry of QCD and the unitarity of the scattering amplitude. We show that the structure of the Λ ( 1405 ) resonance is dominated by the meson–baryon molecular component and is described as a superposition of two independent states. The meson–baryon nature of Λ ( 1405 ) leads to various hadronic molecular states in few-body systems with strangeness which are hadron composite systems driven by the hadronic interactions. We summarize the recent progress in the investigation of the Λ ( 1405 ) structure and future perspective of the physics of the Λ ( 1405 ) resonance.