  We propose a new model which can naturally explain origins of fermion
generations, quark mass hierarchy, and Cabibbo-Kobayashi-Maskawa matrix
simultaneously from geometry of an extra dimension. We take the extra dimension
to be an interval with point interactions, which are additional boundary points
in the bulk space of the interval. Because of the Dirichlet boundary condition
for fermion at the positions of point interactions, profiles of chiral fermion
zero modes are split and localized, and then we can realize three generations
from each five-dimensional Dirac fermion. Our model allows fermion flavor
mixing but the form of non-diagonal elements of fermion mass matrices is found
to be severely restricted due to geometry of the extra dimension. The Robin
boundary condition for a scalar leads to an extra coordinate-dependent vacuum
expectation value, which can naturally explain the fermion mass hierarchy.
