Model-independent predictions of big bang nucleosynthesis

We derive constraints from standard (with Nν = 3) BBN arising solely from two cosmologically produced nuclides, 4He and 7Li, from which the extrapolation to primordial abundances is straightforward. The abundances of D and 3He are at present only inferred from their solar and local interstellar medium values using models of galactic chemical evolution. However, our knowledge of chemical evolution suffers from large uncertainties, and so it is of use to take an approach which minimizes the reliance on chemical evolution in determining the consistency of BBN. Using only the data on 4He and 7Li, and reasonable estimates of possible systematic errors in their abundance determinations, concordance is found if the baryon-to-photon ratio lies in the range 1.4 < 1010η < 3.8 (95% CL). The 4He and 7Li abundances are also used to predict the primordial abundances D and 3He, which provides an initial condition for their chemical evolution.