  We propose an extension of the five dimensional gravitational action with an
external source in order to allow arbitrary smoothing of the negative tension
brane in the Randall-Sundrum model. This extended action can be derived from a
model with an auxiliary four form field coupled to the gravity. We point out a
further generalization of our model in relation to tachyon condensation. A
possible mechanism for radion stabilization in our model is also discussed.
