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

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 $\bar KK$.Comment: 8 pages, 2 figures, contribution to 20th International IUPAP Conference on Few-Body Problems in Physics (FB20), 20-25 August 2011, Fukuoka, Japa

QCD Sum Rules and 1/NcN_c expansion

The 1/$N_c$ arguments are developed to classify the hadronic states in the correlators. Arguments applied to the $\sigma$ meson correlator enable to separate the instanton, glueball, and, in particular, the $\pi\pi$ scattering states by $1/N_c$ from both 2q and 4q correlators. The bare resonance pole with no mixing effects are analyzed with the QCD sum rules (QSR). The results suggest the existence of nontrivial correlation for the mass reduction of 4q system.Comment: Presented at at YITP International Symposium Fundamental Problems in Hot and / or Dense QCD, Kyoto, Japan, 3-6 Mar 200

Theoretical analysis of Lambda(1405) photoproduction

We develop a model that describes the gamma p -> K^+ pi Sigma reaction in the Lambda(1405) region. The model consists of gauge invariant photo-production mechanisms, and the chiral unitary model that gives the rescattering amplitudes where Lambda(1405) is contained. The model also contains phenomenological parameters, associated with short-range dynamics, to be used in fitting data. We successfully fit recent CLAS data for the pi-Sigma invariant mass distributions (line-shape) in the gamma p -> K^+ pi Sigma reaction for all the charge states. We find that the higher mass pole for Lambda(1405) of the chiral unitary model plays an important role in the reaction. We also find the non-resonant background contribution is not negligible, and its sizable effect shifts the Lambda(1405) peak position by several MeV. This work sets a starting point for a fuller analysis in which line-shape as well as K^+ angular distribution data are simultaneously analyzed for extracting Lambda(1405) pole(s).Comment: 5 pages, 6 figures, Contribution to the proceedings of XV International Conference on Hadron Spectroscopy (Hadron 2013), November 4-8 2013, Nara, Japa