Big Bang Nucleosynthesis in Light of Discordant Deuterium Measurements

Two-dimensional concordance plots involving the baryon-to-photon ratio, η, and an effective number of light neutrinos, N v , 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 Lyα clouds have provided discordant 2 H/H determinations: one cloud with a high value of 2 H/H compared with the previously accepted range of ( 2 H+ 3 He)/H, and one system with a significantly lower value of 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 v = 3. The low value of 2 H/H does not fit well with the current observationally inferred primordial abundance of 4 He for N v = 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 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 2 H, 4 He, and 7 Li allows the success of the standard picture for N v =3.