We improve standard big bang nucleosynthesis (SBBN) calculations by taking into account new nuclear physics analyses (the 2003 work of Descouvemont and coworkers). Using a Monte Carlo technique, we calculate the abundances of light nuclei (D, 3 He, 4 He, and 7 Li) versus the baryon-to-photon ratio. The results concerning b h 2 are compared with relevant astrophysical and cosmological observations: the abundance determinations in primitive media and the results from cosmic microwave background (CMB) experiments, especially the Wilkinson Microwave Anisotropy Probe (WMAP) mission. Consistency between WMAP, SBBN results, and D/H data strengthens the deduced baryon density and has interesting consequences on cosmic chemical evolution. A significant discrepancy between the calculated 7 Li abundance deduced from WMAP and the Spite plateau is clearly revealed. To explain this discrepancy, three possibilities are invoked: systematic uncertainties on the Li abundance, surface alteration of Li in the course of stellar evolution, or poor knowledge of the reaction rates related to 7 Be destruction. In particular, the possible role of the up to now neglected 7 Be(d, p)2 and 7 Be(d, ) 5 Li reactions is considered. Another way to reconcile these results coming from different horizons consists of invoking new, speculative primordial physics that could modify the nucleosynthesis emerging from the big bang and perhaps the CMB physics itself. The impressive advances in CMB observations provide a strong motivation for more efforts in experimental nuclear physics and high-quality spectroscopy to keep SBBN in pace.

We use the R-matrix theory to fit low-energy data on nuclear reactions involved in Big Bang nucleosynthesis. A special attention is paid to the rate uncertainties which are evaluated on statistical grounds. We provide S factors and reaction rates in tabular and graphical formats.Comment: 40 pages, accepted for publication at ADNDT, web site at http://pntpm3.ulb.ac.be/bigban

From the observations of the anisotropies of the Cosmic Microwave Background (CMB) radiation, the WMAP satellite has provided a determination of the baryonic density of the Universe, Ω b h 2 , with an unprecedented precision. This imposes a careful reanalysis of the standard Big-Bang Nucleosynthesis (SBBN) calculations. We have updated our previous calculations using thermonuclear reaction rates provided by a new analysis of experimental nuclear data constrained by Rmatrix theory. Combining these BBN results with the Ω b h 2 value from WMAP, we deduce the light element ( 4 He, D, 3 He and 7 Li) primordial abundances and compare them with spectroscopic observations. There is a very good agreement with deuterium observed in cosmological clouds, which strengthens the confidence on the estimated baryonic density of the Universe. However, there is an important discrepancy between the deduced 7 Li abundance and the one observed in halo stars of our Galaxy, supposed, until now, to represent the primordial abundance of this isotope. The origin of this discrepancy, observational, nuclear or more fundamental remains to be clarified. The possible role of the up to now neglected 7 Be(d,p)2α and 7 Be(d,α) 5 Li reactions is considered.

We apply the R-matrix formalism to the 3He(n, p)3H and 7Be(n, p)7Li reactions, which play an important role in the big-bang nucleosynthesis. The cross sections are analysed along with the 4He and 8Be spectra near threshold. Neutron and proton widths of high-energy states are determined. A statistical analysis of the uncertainties provide fairly low error bars (typically 2% at the 1σ confidence level) on the reaction rates.

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