### 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 |
---|---|

Journal | Nuclear Physics A |

Volume | 723 |

Issue number | 1-2 |

DOIs | |

Publication status | Published - Jul 28 2003 |

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### All Science Journal Classification (ASJC) codes

- Nuclear and High Energy Physics

### Cite this

*Nuclear Physics A*,

*723*(1-2). https://doi.org/10.1016/S0375-9474(03)00811-X

**Observational constraints on dark radiation in brane cosmology.** / Ichiki, K.; Yahiro, Masanobu; Kajino, T.; Orito, M.; Mathews, G. J.

Research output: Contribution to journal › Article

*Nuclear Physics A*, vol. 723, no. 1-2. https://doi.org/10.1016/S0375-9474(03)00811-X

}

TY - JOUR

T1 - Observational constraints on dark radiation in brane cosmology

AU - Ichiki, K.

AU - Yahiro, Masanobu

AU - Kajino, T.

AU - Orito, M.

AU - Mathews, G. J.

PY - 2003/7/28

Y1 - 2003/7/28

N2 - 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 4He 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.

AB - 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 4He 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.

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U2 - 10.1016/S0375-9474(03)00811-X

DO - 10.1016/S0375-9474(03)00811-X

M3 - Article

VL - 723

JO - Nuclear Physics A

JF - Nuclear Physics A

SN - 0375-9474

IS - 1-2

ER -