Nonnucleosynthetic Constraints on the Baryon Density and Other Cosmological Parameters

Because the baryon-to-photon ratio eta₁₀ is in some doubt, we drop nucleosynthetic constraints on eta₁₀ and fit the three cosmological parameters (h, Omega_M, eta₁₀) to four observational constraints: Hubble parameter h_o = 0.70 +/- 0.15, age of the universe t_o = 14+7-2 Gyr, cluster gas fraction f_o \≡ f_G h3/2 = 0.060 +/- 0.006, and effective shape parameter Gamma_o = 0.255 +/- 0.017. We experiment with a fifth constraint Omega_o = 0.2 +/- 0.1 from clusters. We set the tilt parameter n = 1 and the gas enhancement factor Upsilon = 0.9. We consider CDM models (open and Omega_M = 1) and flat LambdaCDM models. We test goodness of fit and draw confidence regions by the Delta-chi^2 method. CDM models with Omega_M = 1 (SCDM models) are accepted only because the large error on h_o allows h < 0.5. Baryonic matter plays a significant role in Gamma_o when Omega_M \~ 1. Open CDM models are accepted only for Omega_M \ 0.4. The combination of the four other constraints with Omega_o \≈ 0.2 is rejected in CDM models with 98% confidence, suggesting that light may not trace mass. LambdaCDM models give similar results. In all of these models, eta₁₀ \ 6 is favored strongly over eta₁₀ \ 2. This suggests that reports of low deuterium abundances on QSO lines of sight may be correct, and that observational determinations of primordial 4He may have systematic errors. Plausible variations on n and Upsilon in our models do not change the results much. Only if we drop the crucial Gamma_o constraint are much lower values of Omega_M and eta₁₀ permitted.