No abstract

Primordial nucleosynthesis is one of the three historical evidences for the big bang model, together with the expansion of the universe and the cosmic microwave background. There is a good global agreement between the computed primordial abundances of helium-4, deuterium, helium-3 and their values deduced from observations. Now that the number of neutrino families and the baryonic densities have been fixed by laboratory measurements or CMB observations, the model has no free parameter and its predictions are rigid. Since this is the earliest cosmic process for which we a priori know all the physics involved, departure from its predictions could provide hints or constraints on new physics or astrophysics in the early universe. Precision on primordial abundances deduced from observations has recently been drastically improved and reach the percent level for both deuterium and helium-4. Accordingly, the BBN predictions should reach the same level of precision. For most isotopes, the dominant sources of uncertainty come from those on the laboratory thermonuclear reactions. This article focuses on helium-4 whose predicted primordial abundance depends essentially on weak interactions which control the neutron-proton ratio. The rates of the various weak interaction processes depend on the experimentally measured neutron lifetime, but also includes numerous corrections that we thoroughly investigate here. They are the radiative, zero-temperature, corrections, finite nucleon mass corrections, finite temperature radiative corrections, weak-magnetism, and QED plasma effects, which are for the first time all included and calculated in a self consistent way, allowing to take into account the correlations between them, and verifying that all satisfy detailed balance. Finally, we include the incomplete neutrino decoupling and claim to reach a 10 −4 accuracy on the helium-4 predicted mass fraction of 0.24709 ± 0.00017 (when including the uncertainty on the neutron lifetime). In addition, we provide a Mathematica primordial nucleosynthesis code that incorporates, not only these corrections but also a full network of reactions, using the best available thermonuclear reaction rates, allowing the predictions of primordial abundances of helium-4, deuterium, helium-3 and lithium-7 but also of heavier isotopes up to the CNO region. * Electronic address: pitrou@iap.fr † Electronic address: coc@csnsm.in2p3.fr ‡ Electronic address: uzan@iap.fr § Electronic address: vangioni@iap.fr G. Finite nucleon mass corrections 21 H. Weak magnetism 23 I. Effect of incomplete neutrino decoupling 23 J. Total correction to the weak rates 23 IV. Nucleosynthesis 23 A. Thermonuclear reaction rates 24 B. General form 24 C. Nuclear network and reaction rates uncertainties 25 V. Numerical results 28 A. Overview of PRIMAT 28 B. Temperature of nucleosynthesis 29 C. Effect of corrections on abundances 29 D. Dependence on main parameters 32 E. Distribution of abundance predictions 33 F. Comparison with observations 33 VI. Cosmology with BBN 36 A. Cosmological pert...

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.

Numerical values of charged-particle thermonuclear reaction rates for nuclei in the A=14 to 40 region are tabulated. The results are obtained using a method, based on Monte Carlo techniques, that has been described in the preceding paper of this series (Paper I). We present a low rate, median rate and high rate which correspond to the 0.16, 0.50 and 0.84 quantiles, respectively, of the cumulative reaction rate distribution. The meaning of these quantities is in general different from the commonly reported, but statistically meaningless expressions, "lower limit", "nominal value" and "upper limit" of the total reaction rate. In addition, we approximate the Monte Carlo probability density function of the total reaction rate by a lognormal distribution and tabulate the lognormal parameters µ and σ at each temperature. We also provide a quantitative measure (Anderson-Darling test statistic) for the reliability of the lognormal approximation. The user can implement the approximate lognormal reaction rate probability density functions directly in a stellar model code for studies of stellar energy generation and nucleosynthesis. For each reaction, the Monte Carlo reaction rate probability density functions, together with their lognormal approximations, are displayed graphically for selected temperatures in order to provide a visual impression. Our new reaction rates are appropriate for bare nuclei in the laboratory. The nuclear physics input used to derive our reaction rates is presented in the subsequent paper of this series (Paper III). In the fourth paper of this series (Paper IV) we compare our new reaction rates to previous results.

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

The nuclear physics input used to compute the Monte Carlo reaction rates and probability density functions that are tabulated in the second paper of this series

The effect of variations of the fundamental nuclear parameters on big-bang nucleosynthesis are modeled and discussed in detail taking into account the interrelations between the fundamental parameters arising in unified theories. Considering only 4 He, strong constraints on the variation of the neutron lifetime, neutron-proton mass difference are set. These constraints are then translated into constraints on the time variation of the Yukawa couplings and the fine structure constant. Furthermore, we show that a variation of the deuterium binding energy is able to reconcile the 7 Li abundance deduced from the WMAP analysis with its spectroscopically determined value while maintaining concordance with D and 4 He. The analysis is strongly based on the potential model of Flambaum and Shuryak that relates the binding energy of the deuteron with the nucleon and σ and ω mesons masses, however, we show that an alternative approach that consists of a pion mass dependence necessarily leads to equivalent conclusions.dances in these stars yields [8] Li/H = (1.23 +0.34 −0.16 )×10 −10 and more recently [9] Li/H = (1.26 ± 0.26) × 10 −10 . This value is in clear contradiction with most estimates of the primordial Li abundance, as also shown by [7] who find 7 Li/H = 4.26 +0.73 −0.60 × 10 −10 .(2)

A method based on Monte Carlo techniques is presented for evaluating thermonuclear reaction rates. We begin by reviewing commonly applied procedures and point out that reaction rates that have been reported up to now in the literature have no rigorous statistical meaning. Subsequently, we associate each nuclear physics quantity entering in the calculation of reaction rates with a specific probability density function, including Gaussian, lognormal and chi-squared distributions. Based on these probability density functions the total reaction rate is randomly sampled many times until the required statistical precision is achieved. This procedure results in a median (Monte Carlo) rate which agrees under certain conditions with the commonly reported recommended "classical" rate. In addition, we present at each temperature a low rate and a high rate, corresponding to the 0.16 and 0.84 quantiles of the cumulative reaction rate distribution. These quantities are in general different from the statistically meaningless "minimum" (or "lower limit") and "maximum" (or "upper limit") reaction rates which are commonly reported. Furthermore, we approximate the output reaction rate probability density function by a lognormal distribution and present, at each temperature, the lognormal parameters µ and σ. The values of these quantities will be crucial for future Monte Carlo nucleosynthesis studies. Our new reaction rates, appropriate for bare nuclei in the laboratory, are tabulated in the second paper of this series (Paper II). The nuclear physics input used to derive our reaction rates is presented in the third paper of this series (Paper III). In the fourth paper of this series (Paper IV) we compare our new reaction rates to previous results.