Observational Constraints on Dark Radiation in Brane Cosmology

Details Observational Constraints on Dark Radiation in Brane Cosmology Observational Constraints on Dark Radiation in Brane Cosmology

2002-03-18

arxiv.org/abs/astro-ph/0203272v2

Phys.Rev. D66 (2002) 043521

Astronomy and Astrophysics

Astrophysics

6 pages, 3 figures, submitted to PRD; this version includes the referee's suggestions, updated references, and an improved tre

Scientific paper

10.1103/PhysRevD.66.043521

We analyze the observational constraints on brane-world cosmology whereby the universe is described as a three-brane embedded in a five-dimensional anti-de Sitter space. In this brane-universe cosmology, the Friedmann equation is modified by the appearance of extra terms which derive from existence of the extra dimensions. In the present work we concentrate on the ``dark radiation'' term which diminishes with cosmic scale factor as $a^{-4}$. We show that, although the observational constraints from primordial abundances allow only a small contribution when this term is positive, a much wider range of negative values is allowed. Furthermore, such a negative contribution can reconcile the tension between the observed primordial $\he4$ and D abundances. We also discuss the possible constraints on this term from the power spectrum of CMB anisotropies in the limit of negligible cosmological perturbation on the brane world. We show that BBN limits the possible contribution from dark radiation just before the nucleosynthesis epoch to lie between -65% and $+5%$ of the background photon energy density. Combining this with the CMB constraint reduces this range to between -24% and $+3.5%$ at the $2\sigma$ confidence level.

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