  Experimental evidence suggests that we live in a spatially flat, accelerating
universe composed of roughly one-third of matter (baryonic + dark) and
two-thirds of a negative-pressure dark component, generically called dark
energy. The presence of such energy not only explains the observed accelerating
expansion of the Universe but also provides the remaining piece of information
connecting the inflationary flatness prediction with astronomical observations.
However, despite of its good observational indications, the nature of the dark
energy still remains an open question. In this paper we explore a geometrical
explanation for such a component within the context of brane-world theory
without mirror symmetry, leading to a geometrical interpretation for dark
energy as warp in the universe given by the extrinsic curvature. In particular,
we study the phenomenological implications of the extrinsic curvature of a
Friedman-Robertson-Walker universe in a five-dimensional constant curvature
bulk, with signatures (4,1) or (3,2), as compared with the X-matter (XCDM)
model. From the analysis of the geometrically modified Friedman's equations,
the deceleration parameter and the Weak Energy Condition, we find a consistent
agreement with the presently known observational data on inflation for the
deSitter bulk, but not for the anti-deSitter case.
