  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 meson-baryon scattering amplitude, paying
attention to the charge conservation of the probe interaction. 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 on the real energy axis around the
Lambda(1405) resonance energy, which may be achieved in experiments. Using
sereval 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 Kbar
around N, which gives dominant component inside the Lambda(1405), with escaping
pi Sigma component. Furthermore, we consider Kbar 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 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.
