Big-Bang Nucleosynthesis

TL;DR

This paper reviews the current understanding of Big-Bang nucleosynthesis within the Standard Model, highlighting the concordance of deuterium and helium-4 abundances with CMB data, while noting lithium-7 discrepancies and constraining neutrino species.

Contribution

It provides a comprehensive review of primordial element abundances, their implications for cosmological parameters, and constraints on new physics within the framework of standard cosmology.

Findings

Primordial deuterium and helium-4 abundances are consistent with CMB-derived baryon-to-photon ratio.

Lithium-7 abundance from observations is significantly lower than theoretical predictions.

The effective number of neutrino species is constrained to $N_\nu=3.28 \pm 0.28$.

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, $\eta$, corresponding to the inferred primordial abundances of deuterium and helium-4 is consistent with the independent determination of $\eta$ from 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 $\eta = (5.7-6.7)\times 10^{-10}$ at 95% CL (corresponding to a cosmological baryon density $\Omega_B h^2 = 0.021 - 0.025$). The D and He-4 abundances, when combined with the CMB determination of $\eta$, provide the bound $N_\nu=3.28 \pm 0.28$ on the effective number of neutrino species. Other constraints on new physics are discussed briefly.