Internal structure of the resonant Λ(1405) state in chiral dynamics

The internal structure of the resonant Lambda(1405) state is investigated based on meson-baryon coupled-channels chiral dynamics by evaluating density distributions obtained from the form factors of the Lambda(1405) state. The form factors are defined as an extension of the ordinary stable particles and are directly evaluated from the current-coupled meson-baryon scattering amplitude, paying attention to the charge conservation of the probe interactions. For the resonant Lambda(1405) state we calculate the density distributions in two ways. One is on the pole position of the Lambda(1405) in the complex energy plane, which evaluates the resonant Lambda(1405) structure without contamination from nonresonant backgrounds, and another is on the real energy axis around the Lambda(1405) resonance energy, which may be achieved in experiments. Using several probe interactions and channel decomposition, we separate the various contributions to the internal structure of the Lambda(1405). As a result, we find that the resonant Lambda(1405) state is composed of widely spread (K) over bar around N, which gives dominant component inside the Lambda(1405), with escaping pi Sigma component. Furthermore, we consider (K) over bar N bound state without decay channels, with which we can observe the internal structure of the bound state within real numbers. We also study the dependence of the form factors on the binding energy and meson mass. This verifies that the form factor defined through the current-coupled scattering amplitude serves as a natural generalization of the form factor for the resonance state. The relation between the interaction strength and the meson mass shows that the physical kaon mass appears to be within the suitable range to form a molecular bound state with the nucleon through the chiral SU(3) interaction.