Assessing Big-Bang Nucleosynthesis

Systematic uncertainties in the light-element abundances and their evolution complicate a rigorous statistical assessment. However, using Bayesian methods we show that the following statement is robust: The predicted and measured abundances are consistent with 95% credibility only if the baryon-to-photon ratio is between 2 × ${10}^{-10\mathrm{}}$ and 6.5 × ${10}^{-10\mathrm{}}$ and the number of light neutrino species is less than 3.9. Our analysis suggests that the ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ abundance may have been systematically underestimated.