Big-Bang nucleosynthesis (Particle Data Group mini-review)

Abstract

A critical review is given of the current status of cosmological nucleosynthesis. In the framework of the Standard Model with 3 types of relativistic neutrinos, the baryon-to-photon ratio, $\hat{I}\cdot$, corresponding to the inferred primordial abundances of deuterium and helium-4 is consistent with the independent determination of $\hat{I}\cdot$ from WMAP observations of anisotropies in the cosmic microwave background. However the primordial abundance of lithium-7 inferred from observations is significantly below its expected value. Taking systematic uncertainties in the abundance estimates into account, there is overall concordance in the range $\hat{I}\cdot =(4.7-6.5)x10^{-10}$ @ 95% c.l. (corresponding to a cosmological baryon density $\hat{I}{\text{c◯}}_B{h}^2$ = 0.017 - 0.024). The D and He-4 abundances, together with the CMB determination of $\hat{I}\cdot$, provide the bound $N_{\hat{I}}½=3.24\pm 1.2$ @ 95% c.l. on the effective number of neutrino species. Other constraints on new physics are discussed briefly.

11 pages, 1 (new) figure; from Review of Particle Physics 2006 (http://pdg.lbl.gov/)