UMN-TH-3432/15, FTPI-MINN-15/19.
http://arxiv.org/abs/1505.01076

For a PDF version of the article, click here.

BIG BANG NUCLEOSYNTHESIS: 2015

Richard H. Cyburt

Joint Institute for Nuclear Astrophysics (JINA),
National Superconducting Cyclotron Laboratory (NSCL),
Michigan State University, East Lansing, MI 48824

Brian D. Fields

Departments of Astronomy and of Physics, University of Illinois, Urbana, IL 61801

Keith A. Olive

William I. Fine Theoretical Physics Institute,
School of Physics and Astronomy, University of Minnesota, Minneapolis, MN 55455, USA

Tsung-Han Yeh

Departments of Astronomy and of Physics, University of Illinois, Urbana, IL 61801


Abstract: Big-bang nucleosynthesis (BBN) describes the production of the lightest nuclides via a dynamic interplay among the four fundamental forces during the first seconds of cosmic time. We briefly overview the essentials of this physics, and present new calculations of light element abundances through 6Li and 7Li, with updated nuclear reactions and uncertainties including those in the neutron lifetime. We provide fits to these results as a function of baryon density and of the number of neutrino flavors, Nν. We review recent developments in BBN, particularly new, precision Planck cosmic microwave background (CMB) measurements that now probe the baryon density, helium content, and the effective number of degrees of freedom, Neff. These measurements allow for a tight test of BBN and of cosmology using CMB data alone. Our likelihood analysis convolves the 2015 Planck data chains with our BBN output and observational data. Adding astronomical measurements of light elements strengthens the power of BBN. We include a new determination of the primordial helium abundance in our likelihood analysis. New D/H observations are now more precise than the corresponding theoretical predictions, and are consistent with the Standard Model and the Planck baryon density. Moreover, D/H now provides a tight measurement of Nν when combined with the CMB baryon density, and provides a 2σ upper limit Nν < 3.2. The new precision of the CMB and of D/H observations together leave D/H predictions as the largest source of uncertainties. Future improvement in BBN calculations will therefore rely on improved nuclear cross section data. In contrast with D/H and 4He, 7Li predictions continue to disagree with observations, perhaps pointing to new physics. We conclude with a look at future directions including key nuclear reactions, astronomical observations, and theoretical issues.


Table of Contents

INTRODUCTION

PRELIMINARIES
SBBN
Updated Nuclear Rates
First Results

OBSERVATIONS
Helium-4
Deuterium
Lithium
The Cosmic Microwave Background

THE LIKELIHOOD ANALYSIS
Monte-Carlo Predictions for the Light Elements
The Neutron Mean Life
Planck Likelihood Functions
Results: The Likelihood Functions

THE LITHIUM PROBLEM

LIMITS ON Neff

DISCUSSION

APPENDIX

REFERENCES

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