  Generic cosmological models derived from higher dimensional theories with
warped extra dimensions have a nonzero cosmological constant-like term induced
on the 3+1 space-time, or a physical 3-brane. In the scenario where this 3+1
space-time is an inflating de Sitter "brane" embedded in a higher-dimensional
space-time, described by warped geometry, the 4D cosmological term is
determined in terms of two length scales: one is a scale associated with the
size of extra dimension(s) and the other is a scale associated with the warping
of extra space(s). The existence of this term in four dimensions provides a
tantalizing possibility of explaining the observed accelerating expansion of
the universe from fundamental theories of gravity, e.g. string theory.
