  It has recently been pointed out that global solutions of Einstein's
equations for a 3-brane universe embedded in 4 spatial dimensions give rise to
a 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
this problem by adding cosmological constants to the brane and the bulk, as in
the recent scenario of Randall and Sundrum. Our observation allows for normal
expansion during nucleosynthesis, but faster than normal expansion in the very
early universe, which could be helpful for electroweak baryogenesis, for
example.
