Observational Constraints on Dark Radiation in Brane Cosmology

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.Comment: 6 pages, 3 figures, submitted to PRD; this version includes the referee's suggestions, updated references, and an improved treatment of BBN model uncertaintie

NUCLEAR FUEL CYCLE OBJECTIVES

The nuclear fuel cycle objectives are drawn from many sources, including the conclusions of major international conferences on different stages and aspects of nuclear fuel cycles, many of which are held in cooperation with the IAEA. Experts from various Member States provided advice to the IAEA through a number of consultants meetings and Technical Working Groups (TWGs), such as the TWGs on Nuclear Fuel Performance and Technology, on Nuclear Fuel Cycle Options and Spent Fuel Management, and on Research Reactors, and through the OECD/NEA–IAEA Uranium Group. The IAEA’s International Project on Innovative Nuclear Reactors and Fuel Cycles (INPRO) is another important source of guidance.JRC.E-Institute for Transuranium Elements (Karlsruhe