Richard H Cyburt et al JCAP11(2008)012 doi:10.1088/1475-7516/2008/11/012
Richard H Cyburt1, Brian D Fields2,3 and Keith A Olive4
Show affiliationsThe lithium problem arises from the significant discrepancy between the primordial 7Li abundance as predicted by big bang nucleosynthesis (BBN) theory and the Wilkinson Microwave Anisotropy Probe (WMAP) baryon density, and the pre-Galactic lithium abundance inferred from observations of metal-poor (Population II) stars. This problem has loomed for the past decade, with a persistent discrepancy of a factor of 2–3 in 7Li/H. Recent developments have sharpened all aspects of the Li problem. Namely: (1) BBN theory predictions have sharpened due to new nuclear data; in particular, the uncertainty on the reaction rate for3He(α,γ)7Be has reduced to 7.4%, nearly a factor of 2 tighter than previous determinations. (2) The WMAP five-year data set now yields a cosmic baryon density with an uncertainty reduced to 2.7%. (3) Observations of metal-poor stars have tested for systematic effects. With these, we now find that the BBN+WMAP predicts7Li/H = (5.24−0.67+0.71) × 10−10. The central value represents an increase by 23%, most of which is due to the upward shift in the3He(α,γ)7Be rate. More significant is the reduction in the7Li/H uncertainty by almost a factor of 2, tracking the reduction in the3He(α,γ)7Be error bar. These changes exacerbate the Li problem; the discrepancy is now a factor 2.4 or 4.2σ (from globular cluster stars) to 4.3 or 5.3σ (from halo field stars). Possible resolutions to the lithium problem are briefly reviewed, and key experimental and astronomical measurements highlighted.
97.10.Cv Stellar structure, interiors, evolution, nucleosynthesis, ages
97.10.Tk Abundances, chemical composition
25.55.-e 3H-, 3He-, and 4He-induced reactions
97.20.Tr Population II stars (horizontal branch, metal poor, etc.)
Issue 11 (November 2008)
Received 8 October 2008, accepted for publication 21 October 2008
Published 17 November 2008
Richard H Cyburt et al JCAP11(2008)012
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