Primordial Nucleosynthesis in the New Age of Cosmology: Determining Uncertainties, Examining Concordance, and Probing New Physics
Cyburt, Richard Henry
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https://hdl.handle.net/2142/80493
Description
Title
Primordial Nucleosynthesis in the New Age of Cosmology: Determining Uncertainties, Examining Concordance, and Probing New Physics
Author(s)
Cyburt, Richard Henry
Issue Date
2003
Doctoral Committee Chair(s)
Fields, Brian D.
Department of Study
Physics
Discipline
Physics
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Physics, Nuclear
Language
eng
Abstract
Big bang nucleosynthesis (BBN) has long played a key role in the standard cosmology. BBN accurately predicts the primordial light element abundances of deuterium, helium and lithium. The general concordance between the predicted and observed light element abundances provides a direct probe of the universal baryon density. Recent cosmic microwave background (CMB) anisotropy measurements, particularly the observations performed by the WMAP satellite, examine this concordance by independently measuring the cosmic baryon density. Key to this test of concordance is a quantitative understanding of the uncertainties in the BBN light element abundance predictions. These uncertainties are dominated by systematic errors in nuclear cross sections. We critically analyze the cross section data, producing representations that describe this data and its uncertainties. We take into account the correlations among data, and explicitly treat the systematic errors between data sets. These cross section representations are transformed into thermal rates, and we show that the inclusion of energy correlations helps reduce the uncertainties in these thermal rates. Using these updated nuclear inputs, we compute the new BBN abundance predictions, and quantitatively examine their concordance, first with light element abundance observations and second with CMB anisotropy observations. Overall, there is satisfactory agreement between the CMB and light elements; being excellent for deuterium and marginal for helium-4. However, there exists discordance with lithium-7, suggesting unknown systematics or new physics. If we accept these observations, we can probe nuclear and particle astrophysics. We examine the constraints placed on the number of relativistic degrees of freedom during BBN. New measurements of nuclear cross sections will help reduce the theoretical uncertainties in the light element abundance predictions. New observations of light element abundances will further sharpen BBN's probe of the baryon density. With future observations of the CMB anisotropy, all of these improvements will allow even tighter constraints to be placed on nuclear and particle astrophysics.
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