Statistics – Methodology
Scientific paper
Jan 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996phdt.........5l&link_type=abstract
Thesis (PH.D.)--THE OHIO STATE UNIVERSITY, 1996.Source: Dissertation Abstracts International, Volume: 57-02, Section: B, page: 1
Statistics
Methodology
Baryon Inhomogeneity, Helium Abundance, Big Bang Model
Scientific paper
The standard model of primordial nucleosynthesis has been highly successful in accounting for the observed abundances of D, ^3He, ^4He, and ^7Li with one free parameter of the baryon-to-photon ratio eta. In this work, three separate investigations are presented, called variations in the sense of varying the standard model or varying the methodology for analyzing previously studied topics. The first variation is devoted to testing a recently found correction for the predicted ^4He abundance due to inaccuracy in the commonly used Wagoner computer code. The method of integrating the coupled differential equations of the Wagoner code is replaced by an improved algorithm. The result is the moderately important correction {Delta Y} = +0.0018. The slight difference from the previously found result is explained. The second variation goes beyond the standard model by relaxing the assumption of baryon homogeneity. The standard model seems to indicate the existence of both baryonic and non-baryonic dark matter, and inhomogeneous models are motivated by the potential of obviating the need for one or both. The analysis treats only the simplest case in which the length scale of the baryon perturbation is sufficiently large that diffusion prior to nucleosynthesis can be ignored as well as being of sufficiently small amplitude that gravitational collapse is precluded. What has been lacking in all such studies is a systematic method of testing all possible fluctuation distributions. Such a method is developed here using a discrete analysis and linear programming. While the results confirm the recently recognized possibility of lowering the average baryon density, the upper limit is simply the homogeneous upper bound. The third variation modifies the standard model by adding a decaying particle. It is assumed that the particle dominates the energy density of the universe and then decays with a lifetime tau~10 ^{-1}sec into electromagnetically interacting particles. This product radiation heats electron neutrinos more than the other two neutrino species, resulting in a decrease in the ^4He abundance. Previous calculations of this effect assumed sudden decoupling of the neutrinos from the electromagnetic plasma. Here this calculation is repeated using an improved (although still approximate) treatment of the energy flow from the blackbody radiation into the various neutrino components. The more precise result gives a somewhat smaller reduction in helium than previously found but occurring over a larger range in tau. The reduction in ^4He is as large as {Delta Y} = -0.01 for tau = 0.1-0.7sec. This reduction can resolve the slight discrepancy between standard model predictions and inferred primordial abundances noted in recent studies.
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