Physics
Scientific paper
May 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007jphcs..68a2034t&link_type=abstract
Journal of Physics: Conference Series, Volume 68, Issue 1, pp. 012034 (2007).
Physics
1
Scientific paper
The effective Friedmann equation describing the evolution of a brane Universe in the cosmology of the Randall-Sundrum model includes a dark (or mirage or Weyl) radiation term. The brane evolution can be interpreted as the motion of the brane in an AdSSchwarzschild bulk geometry. The energy density of the dark radiation is proportional to the black hole mass. I review how this result is generalized for an AdS bulk space with an arbitrary matter component. The mirage term retains its form, but the black hole mass is replaced by the covariantly defined integrated mass of the bulk matter. As this mass depends explicitly on the scale factor on the brane, the mirage term does not scale as pure radiation. For low energy densities the brane cosmological evolution is that of a four-dimensional Universe with two matter components: the matter localized on the brane and the mirage matter. There is conservation of energy between the two components. This behaviour indicates a duality between the bulk theory and a four-dimensional theory on the brane. I also discuss the cosmological evolution on a brane with induced gravity within a bulk with arbitrary matter content. The Friedmann equation now has two branches, distinguished by the two possible values of the parameter epsilon = ±1. The branch with epsilon = 1 is characterized by an effective cosmological constant and accelerated expansion for low energy densities. Another remarkable feature is that the contribution from the generalized dark radiation appears with a negative sign. As a result, the presence of the bulk corresponds to an effective negative energy density on the brane, without violation of the weak energy condition. In the branch with epsilon = 1 the transition from a period of domination of the matter energy density by non-relativistic brane matter to domination by the generalized dark radiation can lead to a crossing of the phantom divide w = -1.
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