Complementary constraints on brane cosmology

The acceleration of the expansion of the universe represents one of the major challenges to our current understanding of fundamental physics. In principle, to explain this phenomenon, at least two different routes may be followed: either adjusting the energy content of the Universe-by introducing a negative-pressure dark energy-or modifying gravity at very large scales-by introducing new spatial dimensions, an idea also required by unification theories. In the cosmological context, the role of such extra dimensions as the source of the dark pressure responsible for the acceleration of our Universe is translated into the so-called brane world (BW) cosmologies. Here we study complementary constraints on a particular class of BW scenarios in which the modification of gravity arises due to a gravitational leakage into extra dimensions. To this end, we use the most recent Chandra measurements of the X-ray gas mass fraction in galaxy clusters, the WMAP determinations of the baryon density parameter, measurements of the Hubble parameter from the HST, and the current supernova data. In agreement with other recent results, it is shown that these models provide a good description for these complementary data, although a closed scenario is always favored in the joint analysis. If we restrict our analysis to the flat case, in accordance with the latest CMB measurements, we found that the so-called "concordance model", i.e., a flat Lambda CDM universe, provides a slightly better fit to this particular combination of observational data than does a BW model. We, however, emphasize that observational tests of BW scenarios constitute a natural verification of the role of possible extra dimensions in both fundamental physics and cosmology.