The latest nuclear reaction cross sections (including the most recent determinations of the neutron lifetime) are used to recalculate the abundances of deuterium, 3He, 4He, and 7Li within the framework of primordial nucleosynthesis in the standard (homogeneous and isotropic) hot, big bang model. The observational data leading to estimates of (or bounds to) the primordial abundances of the light elements is reviewed with an emphasis on 7Li and 4He. A comparison between theory and observation reveals the consistency of the predictions of the standard model and leads to bounds to the nucleon-to-photon ratio, 2.8 ≤ η10 ≤ 4.0 (η10 ≡ 1010nB/nγ), which constrains the baryon density parameter, ΩBh502 = 0.05 ± 0.01 (the Hubble parameter is H0 = 50h50 km s-1 Mpc-1). These bounds imply that the bulk of the baryons in the universe are dark if ΩTOT = 1 and would require that the universe be dominated by nonbaryonic matter. An upper bound to the primordial mass fraction of 4He, Yp ≤ 0.240, constrains the number of light (equivalent) neutrinos to Nv ≤ 3.3, in excellent agreement with the LEP and SLC collider results. Alternatively, for Nv = 3, we bound the predicted primordial abundance of 4He: 0.236 ≤ Yp ≤ 0.243 (for 882 ≤ τn ≤ 896 s).
- Early universe
- Elementary particles