Hadronic few-body systems in chiral dynamics, -- Few-body systems in hadron physics --

Abstract

Hadronic composite states are introduced as few-body systems in hadron physics. The $\Lambda(1405)$ resonance is a good example of the hadronic few-body systems. It has turned out that $\Lambda(1405)$ can be described by hadronic dynamics in a modern technology which incorporates coupled channel unitarity framework and chiral dynamics. The idea of the hadronic $\bar KN$ composite state of $\Lambda(1405)$ 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-wave $\bar K$ couplings, there are few-body quasibound states with kaons systematically just below the break-up thresholds, like $\bar KNN$, $\bar KKN$ and $\bar KKK$, as well as $\Lambda(1405)$ as a $\bar KN$ quasibound state and $f_{0}(980)$ and $a_{0}(980)$ as $\bar KK$.