  We study the parameter dependence of the internal structure of resonance
states by formulating Complex two-dimensional (2D) Matrix Model, where the two
dimensions represent two-levels of resonances. We calculate a critical value of
the parameter at which "nature transition" with character exchange occurs
between two resonance states, from the viewpoint of geometry on
complex-parameter space. Such critical value is useful to know the internal
structure of resonance states with variation of the parameter in the system. We
apply the model to analyze the internal structure of hadrons with variation of
the color number Nc from infinity to a realistic value 3. By regarding 1/Nc as
the variable parameter in our model, we calculate a critical color number of
nature transition between hadronic states in terms of quark-antiquark pair and
mesonic molecule as exotics from the geometry on complex-Nc plane. For the
large-Nc effective theory, we employ the chiral Lagrangian induced by
holographic QCD with D4/D8/D8-bar multi-D brane system in the type IIA
superstring theory.
