The nature of Λ(1405) hyperon resonance in chiral dynamics

The nature of the Λ(1405) is discussed based on the unitarised coupled-channels approach with chiral dynamics (chiral unitary model). This approach describes the scattering cross sections and the Λ(1405) spectra phenomenologically very well. With this successful description of Λ(1405), it is found that the Λ(1405) is composed by two resonance states having different coupling nature to the meson-baryon states. As a consequence, the resonance position in the πΣ invariant mass spectrum depends on the initial channel of the Λ(1405) production. To observe the Λ(1405) initiated by the channel, K−d→Λ(1405)n is one of the most favorable reactions. Hadronic molecule states with kaons are also discussed by emphasizing an important role of Λ(1405) as a quasibound state of