Primordial lithium abundance as a stringent constraint on the baryonic content of the universe

We have refined the estimate of the primordial level of Li-7 abundance to a n 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 L i abundance of A(Li)(p) = 2.07(-0.04)(+0.16) after taking into account poss ible systematic errors in the estimation of Li abundances, with the excepti on of a still controversial issue regarding stellar depletion. The inferred value of eta (the baryon-to-photon number density ratio in the universe) b ased 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 st ellar 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), should be taken as an independent constraint on the baryonic mass density p arameter in the universe, giving Omega(b)h(2) = (0.64-1.4) x 10(-2) with h = H-0/100 km s(-1) Mpc(-1).