The cosmic microwave background: gaussianity and polarization
Larson, David Leonard
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https://hdl.handle.net/2142/34779
Description
Title
The cosmic microwave background: gaussianity and polarization
Author(s)
Larson, David Leonard
Issue Date
2006-10
Doctoral Committee Chair(s)
Wandelt, Benjamin D.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Cosmic Microwave Background (CMB)
Mathematical Properties
Non-Gaussianity
Gibbs Sampling
Language
en
Abstract
The Cosmic Microwave Background (CMB) is a window to the earliest parts of the universe that we can still directly see. As such, it provides excellent data for testing the currently accepted model of cosmology: an expanding Friedmann-Robertson-Walker spacetime that is statistically described by about six parameters. This dissertation presents three tools for probing that standard model of cosmology and tests them on real CMB data.
The first tool checks the peaks and valleys in the CMB to make sure they statistically match those expected from a Gaussian random field, as predicted by our standard model. To do this, we analyze the one- and two-point correlation functions and compare those to simulated Gaussian skies with the same power spectrum and noise. We find some discrepancies in the WMAP data, and we can interpret these as either a detection of non-Gaussianity, or some foreground or other overlooked detail in our model of the experiment. The second tool provides a statistically sound and relatively rapid technique for estimating the polarized power spectrum of the CMB. This is the Gibbs sampler, applied to power spectra; it samples the power spectra according to either the likelihood, or Bayesian posterior probability, as desired. These samples accurately reflect the error bars on the power spectra, and a correct understanding of the error bars is essential to assuring that our standard model properly predicts the power spectra. We demonstrate this tool on the COBE data, polarized simulations, and the polarized 3-year WMAP data. The third tool we present is a method of visualizing the CMB, which is useful for displaying polarized fields in an easily understood fashion. While this does not directly test the standard model, it does provide a way to more clearly understand our data and look for possible unwanted artifacts, such as polarized
Iii foregrounds. As a way to detect contaminants in the CMB data, it will be very useful when trying to test the standard model of cosmology.
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