D-branes, string cosmology, and large extra dimensions - art. no. 123506

D-branes are fundamental in all scenarios where there are large extra dimen sions and the string scale is much smaller than the four-dimensional Planck mass. We show that this current picture predicts a period of inflation on our brane which is driven by the large extra dimensions and the issue of th e graceful exit becomes inextricably linked to the problem of the stabiliza tion of the extra dimensions, suggesting the possibility of a common soluti on. We also show that branes may violently fluctuate along their transverse directions in curved spacetime, possibly leading to a period of brane-driv en inflation. This phenomenon plays also a crucial role in many other cosmo logical issues, such as the smoothing out of the cosmological singularities .