In the proceedings of the May 2003 STScI Symposium, "The Local Group as an Astrophysical Laboratory".
astro-ph/0308511

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Abstract. The primordial abundances of deuterium, helium-3, helium-4, and lithium-7 probe the baryon density of the Universe only a few minutes after the Big Bang. Of these relics from the early Universe, deuterium is the baryometer of choice. After reviewing the current observational status of the relic abundances (a moving target!), the baryon density determined by big bang nucleosynthesis (BBN) is derived. The temperature fluctuation spectrum of the cosmic background radiation (CBR), established several hundred thousand years later, probes the baryon density at a completely different epoch in the evolution of the Universe. The excellent agreement between the BBN- and CBR-determined baryon densities provides impressive confirmation of the standard model of cosmology, permitting the study of extensions of the standard model. In combination with the BBN- and/or CBR-determined baryon density, the relic abundance of ⁴He provides an excellent chronometer, constraining those extensions of the standard model which lead to a nonstandard early-Universe expansion rate.

Table of Contents

INTRODUCTION

A BBN PRIMER

Early-Universe Expansion Rate

The Baryon Density

BBN ABUNDANCES

Relic Abundances

Deuterium - The Baryometer Of Choice

Helium-3

Lithium-7

Helium-4 - The BBN Chronometer

THE BARYON DENSITY FROM SBBN

THE BARYON DENSITY FROM THE CBR

NONSTANDARD BBN: S 1, N 3

NONSTANDARD CBR: S 1, N 3

SUMMARY AND CONCLUSIONS

REFERENCES