Journal
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
Volume -, Issue 1, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.1088/1475-7516/2006/01/016
Keywords
dark energy theory; cosmology with extra dimensions; cosmological perturbation theory
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The DGP brane-world model provides an alternative to the standard LCDM cosmology, in which the late universe accelerates due to a modi. cation of gravity rather than vacuum energy. The cosmological constant. in LCDM is replaced by a single parameter, the crossover scale r(c), in DGP. The supernova redshift observations can be fitted by both models, with Lambda similar to H-0(2) and rc similar to H-0(-1) This degeneracy is broken by structure formation, which is suppressed in di. erent ways in the two models. There is some confusion in the literature about how the standard linear growth factor is modified in the DGP model. While the luminosity distance can be computed purely from the modified four-dimensional Friedman equation, the evolution of density perturbations requires an analysis of the five-dimensional gravitational field. We show that if the five-dimensional effects are inappropriately neglected, then the four-dimensional Bianchi identities are violated and the computed growth factor is incorrect. By using the five-dimensional equations, we derive the correct growth factor.
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