40,507 research outputs found

    Coulomb screening in linear coasting nucleosynthesis

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    We investigate the impact of coulomb screening on primordial nucleosynthesis in a universe having scale factor that evolves linearly with time. Coulomb screening affects primordial nucleosynthesis via enhancement of thermonuclear reaction rates. This enhancement is determined by the solving Poisson equation within the context of mean field theory (under appropriate conditions during the primordial nucleosynthesis). Using these results, we claim that the mean field estimates of coulomb screening hardly affect the predicted element abundances and nucleosynthesis parameters,{η9,ξe}, \{\eta_9,\xi_e\}. The deviations from mean field estimates are also studied in detail by boosting genuine screening results with the screening parameter (ωs\omega_s). These deviations show negligible effect on the element abundances and on nucleosynthesis parameters. This work thus rules out the coulomb screening effects on primordial nucleosynthesis in slow evolving models and confirms that constraints in ref.[7] on nucleosynthesis parameters remain unaltered.Comment: 14 pages,11 figur

    Inhomogeneous Big-Bang Nucleosynthesis in Light of Recent Observations

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    We consider inhomogeneous big bang nucleosynthesis in light of the present observational situation. Different observations of He-4 and D disagree with each other, and depending on which set of observations one uses, the estimated primordial He-4 corresponds to a lower baryon density in standard big bang nucleosynthesis than what one gets from deuterium. Recent Kamiokande results rule out a favorite particle physics solution to this tension between He-4 and D. Inhomogeneous nucleosynthesis can alleviate this tension, but the more likely solution is systematics in the observations. The upper limit to Omega_b from inhomogeneous nucleosynthesis is higher than in standard nucleosynthesis, given that the distance scale of the inhomogeneity is near the optimal value, which maximizes effects of neutron diffusion. Possible sources of baryon inhomogeneity include the QCD and electroweak phase transitions. The distance scale of the inhomogeneities arising from the electroweak transition is too small for them to have a large effect on nucleosynthesis, but the effect may still be larger than some of the other small corrections recently incorporated to SBBN codes.Comment: 12 pages, 8 figures, REVTe

    Primordial Nucleosynthesis

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    Primordial nucleosynthesis, or Big-Bang Nucleosynthesis (BBN), is one of the three evidences for the Big-Bang model, together with the expansion of the Universe and the Cosmic Microwave Background. There is a good global agreement over a range of nine orders of magnitude between abundances of 4He, D, 3He and 7Li deduced from observations, and calculated in primordial nucleosynthesis. This comparison was used to determine the baryonic density of the Universe. For this purpose, it is now superseded by the analysis of the Cosmic Microwave Background (CMB) radiation anisotropies. However, there remain, a yet unexplained, discrepancy of a factor 3-5, between the calculated and observed lithium primordial abundances, that has not been reduced, neither by recent nuclear physics experiments, nor by new observations. We review here the nuclear physics aspects of BBN for the production of 4He, D, 3He and 7Li, but also 6Li, 9Be, 11B and up to CNO isotopes. These are, for instance, important for the initial composition of the matter at the origin of the first stars. Big-Bang nucleosynthesis, that has been used, to first constrain the baryonic density, and the number of neutrino families, remains, a valuable tool to probe the physics of the early Universe, like variation of "constants" or alternative theories of gravity.Comment: Invited Plenary Talk given at the 11th International Conference on Nucleus-Nucleus Collisions (NN2012), San Antonio, Texas, USA, May 27-June 1, 2012. To appear in the NN2012 Proceedings in Journal of Physics: Conference Series (JPCS

    Recommendations for Monte Carlo nucleosynthesis sampling (Research Note)

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    Context: Recent reaction rate evaluations include reaction rate uncertainties that have been determined in a statistically meaningful manner. Furthermore, reaction rate probability density distributions have been determined and published in the form of lognormal parameters with the specific goal of pursuing Monte Carlo nucleosynthesis studies. Aims: To test and assess different methods of randomly sampling over reaction rate probability densities and to determine the most accurate method for estimating elemental abundance uncertainties. Methods: Experimental Monte Carlo reaction rates are first computed for the 22Ne+alpha, 20Ne(p,g)21Na, 25Mg(p,g)26Al, and 18F(p,alpha)15O reactions, which are used to calculate reference nucleosynthesis yields for 16 nuclei affected by nucleosynthesis in massive stars and classical novae. Five different methods of randomly sampling over these reaction rate probability distributions are then developed, tested, and compared with the reference nucleosynthesis yields. Results: Given that the reaction rate probability density distributions can be described accurately with a lognormal distribution, Monte Carlo nucleosynthesis variations arising from the parametrised estimates for the reaction rate variations agree remarkably well with those obtained from the true rate samples. Most significantly, the most simple parametrisation agrees within just a few percent, meaning that Monte Carlo nucleosynthesis studies can be performed reliably using lognormal parametrisations of reaction rate probability density functions.Comment: 6 pages, 3 figures. Accepted to Astronomy & Astrophysics as a Research Not
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