Model independent predictions of big bang nucleosynthesis from ⁴He and ⁷Li: Consistency and implications

We examine in detail how BBN theory is constrained, and what predictions it can make, when using only the most model-independent observational constraints. We avoid the uncertainties and model-dependencies that necessarily arise when solar neighborhood D and ³He abundances are used to infer primordial D and ³He via chemical and stellar evolution models. Instead, we use ⁴He and ⁷Li, thoroughly examining the effects of possible systematic errors in each. Via a likelihood analysis, we find near perfect agreement between BBN theory and the most model-independent data. Given this agreement, we then assume the correctness of BBN to set limits on the single parameter of standard BBN, the baryon-to-photon ratio, and to predict the primordial D and ³He abundances. For the baryon-to-photon ratio, η, we find a best value, η = 1.8 × 10^-10, corresponding to Ω_Bh² = 0.0066. We also repeat our analysis including recent measurements of D/H from quasar absorption systems and find that the near perfect agreement between theory and observation of the three isotopes, D, ⁴He and ⁷Li is maintained. These results have strong implications for the chemical and stellar evolution of the light elements, in particular for ³He. In addition, our results (especially if the D/H measurements are confirmed) have implications for the stellar depletion of ⁷Li. Finally, we set limits on the number N_v of neutrino flavors, using an analysis which carefully and systematically includes all available experimental constraints. The value N_v = 3.0 fits best with BBN and a 95% CL upper limit of N_v ≤ 4 is established.