Supersymmetry and Brane Cosmology

We consider a five-dimensional brane world scenario where the fifth dimensionis compactified on $S^1/Z_2$. We show that the familiar four-dimensionalcosmology on our brane is easily recovered during a primordial stage ofinflation if supersymmetry is exploited. Even if some vacuum energy densityappears localized on our three brane, heavy supersymmetric bulk fields adjustthemselves and acquire a nontrivial configuration along the extra-dimension.This phenomenon redistributes uniformly the energy density across the bulk andthe resulting energy-momentum tensor does not display any singularityassociated to the initial localized energy density on our three-brane. No jumpsacross the brane are present for the derivatives of the metric and Einstein'sequations are solved by constant solutions along the fifth dimension. Ourfindings make it clear that cosmological phenomena in the supersymmetric braneworld scenario must be studied taking properly into account bulk supersymmetricstates. This comment is particularly relevant when applied to (super)gravitysince in supersymmetric brane world scenarios, even though chiral matter andgauge fields may be restricted to live on boundaries, gravity multiplets alwayspropagate in the bulk.Comment: LaTeX file, 12 page