In Annual Review of Nuclear and Particle Science, vol. 61, issue 1, pp. 47-68, 2011.
http://arxiv.org/abs/1203.3551

For a PDF version of the article, click here.

THE PRIMORDIAL LITHIUM PROBLEM

Brian D. Fields


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


Abstract: Big-bang nucleosynthesis (BBN) theory, together with the precise WMAP cosmic baryon density, makes tight predictions for the abundances of the lightest elements. Deuterium and 4He measurements agree well with expectations, but 7Li observations lie a factor 3−4 below the BBN+WMAP prediction. This 4−5 σ mismatch constitutes the cosmic “lithium problem,” with disparate solutions possible. (1) Astrophysical systematics in the observations could exist but are increasingly constrained. (2) Nuclear physics experiments provide a wealth of well-measured cross-section data, but 7Be destruction could be enhanced by unknown or poorly-measured resonances, such as 7Be + 3He → 10C*p + 9B. (3) Physics beyond the Standard Model can alter the 7Li abundance, though D and 4He must remain unperturbed; we discuss such scenarios, highlighting decaying Supersymmetric particles and time-varying fundamental constants. Present and planned experiments could reveal which (if any) of these is the solution to the problem.


Key Words : big bang nucleosynthesis, early universe, dark matter, abundances of light elements, extensions of the Standard Model


Table of Contents

INTRODUCTION

STANDARD BBN IN LIGHT OF WMAP: THE LITHIUM PROBLEM EMERGES
Standard BBN Theory
Light Element Observations
Microwave Background Anisotropies as a Cosmic Baryometer
Assessing Standard BBN: the Lithium Problem(s) Revealed

SOLUTIONS TO THE LITHIUM PROBLEM(S)
Astrophysical Solutions
Nuclear Physics Solutions
Solutions Beyond the Standard Model

DISCUSSION AND OUTLOOK

REFERENCES

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