Cosmological implications of two conflicting deuterium abundances

Constraints on big bang nucleosynthesis (BBN) and on cosmological parameters from conflicting deuterium observations in different high redshift QSO systems are discussed. The high deuterium observations by Carswell et al., Songaila et al., and Rugers and Hogan are consistent with ⁴He and ⁷Li observations and standard BBN (N_ν =3) and allows N_ν<~3.6 at 95% C.L., but are inconsistent with local observations of D and ³He in the context of conventional theories of stellar and galactic evolution. In contrast, the low deuterium observations by Tytler, Fan, and Burles and Burles and Tytler are consistent with the constraints from local galactic observations, but require N_ν=1.9±0.3 at 68% C.L., excluding standard BBN at 99.9% C.L., unless the systematic uncertainties in the ⁴He observations have been underestimated by a large amount. The high and low primordial deuterium abundances imply, respectively, ΩBh²=0.005--$0.01$ and ΩBh²=0.02--$0.03$ at 95% C.L. When combined with the high baryon fraction inferred from x-ray 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.