Cosmological Expansion in the Presence of an Extra Dimension

It has recently been pointed out that global solutions of Einstein's for a 3-brane universe embedded in 4 spatial dimensions give rise to Friedmann equation of the form H ~ rho on the brane, instead of the usual H ~ (rho) ^1/2, which is inconsistent with cosmological observations. We remedy problem by adding cosmological constants to the brane and the bulk, as in recent scenario of Randall and Sundrum. Our observation allows for normal during nucleosynthesis, but faster than normal expansion in the very universe, which could be helpful for electroweak baryogenesis, for.