Big Bang Nucleosynthesis in Light of Discordant Deuterium Measurements

Abstract

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