Primordial Nucleosynthesis: The Predicted and Observed Abundances and Their Consequences

TL;DR

This paper reviews the predictions of primordial light element abundances from big bang nucleosynthesis, compares them with observations, and discusses implications for cosmological parameters and early Universe models.

Contribution

It provides a comprehensive review of BBN predictions, observational data, and their implications for standard and non-standard cosmological models.

Findings

Predicted and observed abundances of light elements are consistent within uncertainties.

Primordial nucleosynthesis constrains the baryon density parameter.

Comparisons with cosmic background radiation support standard cosmological models.

Abstract

For a brief time in its early evolution the Universe was a cosmic nuclear reactor. The expansion and cooling of the Universe limited this epoch to the first few minutes, allowing time for the synthesis in astrophysically interesting abundances of only the lightest nuclides (D, 3He, 4He, 7Li). For big bang nucleosynthesis (BBN) in the standard models of cosmology and particle physics (SBBN), the SBBN-predicted abundances depend on only one adjustable parameter, the baryon density parameter (the ratio by number of baryons (nucleons) to photons). The predicted and observed abundances of the relic light elements are reviewed, testing the internal consistency of primordial nucleosynthesis. The consistency of BBN is also explored by comparing the values of the cosmological parameters inferred from primordial nucleosynthesis for the standard model and for models with non-standard early Universe expansion rates with those determined from studies of the cosmic background radiation, which provides a snapshot of the Universe some 400 thousand years after BBN ended.