  The radion equilibrium in the Randall-Sundrum (RS) model is guaranteed by the
back-reaction of a bulk scalar field. In this paper we study an extended
scenario, where an intermediate brane exists in addition to the two branes at
the fixed points, due to the discontinuity of bulk cosmology constants in two
spatial regions. We conducted a complete analysis of the linearized Einstein's
equations after applying the Goldberger-Wise mechanism. Our result elucidates
that in the presence of nonfixed point branes under the rigid assumption, a
unique radion field is conjectured as legitimate in the RS metric perturbation.
The cosmological expansion in this setup is briefly discussed.
