## Abstract

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 ≤_{d}ark 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 ^{4}He 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 e^{+}e^{-} annihilation epoch to lie between -123% and +11% of the background photon energy density. Combining this with the CMB constraint reduces this range to between -41% and +10.5% at the 2σ confidence level.

Original language | English |
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Pages (from-to) | 386-388 |

Number of pages | 3 |

Journal | Nuclear Physics A |

Volume | 723 |

Issue number | 1-2 |

DOIs | |

Publication status | Published - Jul 28 2003 |

Externally published | Yes |

## All Science Journal Classification (ASJC) codes

- Nuclear and High Energy Physics