Primordial nucleosynthesis in light of WMAP

Richard H Cyburt,Brian D Fields,Keith A Olive

doi:10.1016/j.physletb.2003.06.026

Richard H Cyburt, Brian D Fields + Show 1 more

Open Access

https://doi.org/10.1016/j.physletb.2003.06.026

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Abstract

Big bang nucleosynthesis has long provided the primary determination of the cosmic baryon density ΩBh2, or equivalently the baryon-to-photon ratio, η. Recently, data on CMB anisotropies have become increasingly sensitive to η. The comparison of these two independent measures provides a key test for big bang cosmology. The first release of results from the Wilkinson Microwave Anisotropy Probe (WMAP) marks a milestone in this test. With the precision of WMAP, the CMB now offers a significantly stronger constraint on η. We discuss the current state of BBN theory and light element observations (including their possible lingering systematic errors). The resulting BBN baryon density prediction is in overall agreement with the WMAP prediction, an important and non-trivial confirmation of hot big bang cosmology. Going beyond this, the powerful CMB baryometer can be used as an input to BBN and one can accurately predict the primordial light element abundances. By comparing these with observations one can obtain new insight into post-BBN nucleosynthesis processes and associated astrophysics. Finally, one can test the possibility of nonstandard physics at the time of BBN, now with all light elements available as probes. Indeed, with the WMAP precision η, deuterium is already beginning to rival 4He's sensitivity to nonstandard physics, and additional D/H measurements can improve this further.

Highlights

The primordial light element abundances are predicted accurately and robustly by the theory of Big Bang Nucleosynthesis (BBN) [1, 2], describing the first 3 minutes of the hot early universe
The Cosmic Microwave Background (CMB), and its anisotropies carry key information about the content of the universe and early structure growth. Both BBN and the CMB are sensitive to the baryon content in the universe and because they are governed by different physics, BBN and the CMB can be used as independent measures of the cosmic baryon density, ρB ∝ ΩBh2, or equivalently the baryon-to-photon ratio, η
The comparison of the baryon density predictions from BBN and the CMB is a fundamental test of big bang cosmology [3], and its underlying assumptions, which include: a nearly homogeneous, isotropic universe, with gravity described by General Relativity and microphysics described by the Standard Model of particle physics

Summary

Introduction

The primordial light element abundances are predicted accurately and robustly by the theory of Big Bang Nucleosynthesis (BBN) [1, 2], describing the first 3 minutes of the hot early universe. With the first data release from the Wilkinson Microwave Anisotropy Probe (WMAP), the anisotropies in the CMB have been measured to unprecedented accuracy [4] This new precision allows for a CMB-based determination of the baryon density which is significantly tighter than current BBN analysis yields. Prior to the recent measurements of the microwave background power spectrum, the best available method for determining the baryon density of Universe was the concordance of the BBN predictions and the observations of the light element abundances of D, 3He, 4He, and 7Li. A high-confidence upper limit to the baryon density has long been available [7] from observations of local D/H abundance determinations (giving roughly η10 < 9.0), but a reliable lower bound to η, much less a precise value, has been more elusive to obtain. More weight has been given to the D/H determinations because of their excellent agreement with the (pre-WMAP) CMB experiments

The Baryon Density from the CMB and Beyond

Using BBN and the CMB to Probe Astrophysics

Using BBN and the CMB to Probe Particle Physics

Findings

Discussion and Conclusions