We have refined the estimate of the primordial level of ^ { 7 } Li 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 ^ { +0.16 } _ { -0.04 } , 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 \eta ( 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 \Omega _ { b } h ^ { 2 } = ( 0.64 - 1.4 ) \times 10 ^ { -2 } with h = H _ { 0 } / 100 km s ^ { -1 } Mpc ^ { -1 } .