Abstract
We study the averaged action of the Randall–Sundrum model with a time-dependent metric ansatz. It can be reformulated in terms of a Brans–Dicke action with time-dependent Newton's constant. We show that the physics of the early universe, particularly inflation, is governed by the Brans–Dicke theory. The Brans–Dicke scalar, however, quickly settles to its equilibrium value and decouples from the post-inflationary cosmology. The deceleration parameter is negative to start with but changes sign before the Brans–Dicke scalar settles to its equilibrium value. Consequently, the brane metric smoothly exits inflation. We have also studied the slow-roll inflation in our model and investigated the spectra of the density perturbation generated by the radion field and find them consistent with the current observations.