Cosmological Implications of Two Conflicting Deuterium Abundances

Constraints on big bang nucleosynthesis (BBN) and on cosmological parameters from conflicting deuterium observations in different high red-shift QSO systems are discussed. The high deuterium observations by Carswell et al., Songaila et al., and Rugers & Hogan is consistent with He and Li observations and Standard BBN (Nν =3) and allows Nν ≤ 3.6 at 95% C.L., but is inconsistent with local observations of D and He in the context of conventional theories of stellar and Galactic evolution. In contrast, the low deuterium observations by Tytler, Fan & Burles and Burles & Tytler are consistent with the constraints from local Galactic observations, but require Nν = 1.9 ± 0.3 at 68% C.L., excluding Standard BBN at 99.9% C.L., unless the systematic uncertainties in the He observations have been underestimated by a large amount. The high and low primordial deuterium abundances imply, respectively, ΩBh 2 = 0.005 − 0.01 and ΩBh 2 = 0.02 − 0.03 at 95% C.L. When combined with the high baryon fraction inferred from xray observations of rich clusters, the corresponding total mass densities (for 50 ≤ H0 ≤ 90) are ΩM = 0.05 − 0.20 and ΩM = 0.2 − 0.7, respectively (95% C.L.) The range of ΩM corresponding to high D is in conflict with dynamical constraints (ΩM ≥ 0.2 − 0.3) and with the shape parameter constraint (Γ = ΩMh = 0.25 ± 0.05) from large scale structure formation in CDM and ΛCDM models. Typeset using REVTEX