Big-Bang Nucleosynthesis in Light of Discordant Deuterium Measurements

Abstract

Two dimensional concordance plots involving the baryon-to-photon ratio, $\eta$, and an effective number of light neutrinos, $N_{\nu }$, are used to discuss the overall consistency of standard big-bang nucleosynthesis in light of recent determinations of the primordial deuterium (${}^2$H) abundance. Observations of high-redshift Ly-$\alpha$ clouds have provided discordant ${}^2$H/H determinations: one cloud with ${}^2$H/H high compared with the previously accepted upper limit on (${}^2$H + ${}^3$He)/H; and one system with a significantly lower upper bound on ${}^2$H/H than those previously obtained. The high value of ${}^2$H/H agrees well with the current observationally-inferred primordial abundances of ${}^4$He and ${}^7$Li for $N_{\nu }=3$. The low value of ${}^2$H/H does not fit well with the current observationally-inferred primordial abundance of ${}^4$He for $N_{\nu }=3$. In addition, if the low value of ${}^2$H/H is indicative of the primordial deuterium abundance, then significant depletion of ${}^7$Li in old, hot Pop II halo stars is probably required to obtain a concordant range of $\eta$, for {\em any} effective number of neutrino flavors. The use of conservative ranges for the primordial abundances of ${}^2$H, ${}^4$He, and ${}^7$Li allow success of the standard picture for $N_{\nu }=3$.

Comments: Latex 14 pages, uses aastex macros, submitted to Apj