We have refined the estimate of the primordial level of 7Li abundance to an accuracy better than 10%, based on high-precision Li abundances for metal-poor halo stars and a recent model of post-BBN (big bang nucleosynthesis) chemical evolution that provides a quantitative explanation of the detected gentle ascent of the Spite plateau for stars with metallicities [Fe/H] -3. Our maximum likelihood analysis obtains an estimate for the primordial Li abundance of A(Li)p = 2.07 after taking into account possible systematic errors in the estimation of Li abundances, with the exception of a still controversial issue regarding stellar depletion. The inferred value of η (the baryon-to-photon number density ratio in the universe) based on this estimate is more consistent with that derived from the set of reported "low He"+"high D" from extragalactic sites than that derived from reported "high He"+"low D" measurements. Since, within current models of stellar depletion processes, it is difficult to account for the observed very small scatter of Li abundance in metal-poor stars, our estimate of A(Li)p should be taken as an independent constraint on the baryonic mass density parameter in the universe, giving Ωbh2 = (0.64-1.4) × 10-2 with h = H0/100 km s-1 Mpc-1.
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