Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.542180
Title: Local methods for the cosmic microwave background
Author: Bowyer, Jude William
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2011
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Abstract:
The standard tools for analyzing the Cosmic Microwave Background (CMB), a key component for making cosmological inferences, are usually of global sampling type. Such a methodological bias may preclude the development of important techniques for cosmology. This thesis develops local, real-space tools for CMB analysis which may be complemented using harmonic space techniques or provide useful signal diagnostics on their own. Particularly, finite-difference schemes for performing local derivatives are investigated. One can define derivatives which extract the primordial polarization modes from the measured CMB Stokes parameters by constructing real scalar and pseudo-scalar fields. The detection of a primordial curl-like (‘B’-mode) CMB polarization signal would imply the existence of a background of primordial gravitational waves, the ‘smoking gun’ signal of an inflationary cosmology. On an obscured (masked) sky, the gradient-like (‘E’-mode) signal leaks into the B-mode signal when the standard harmonic E/B signal decomposition is performed — using local techniques instead, this leakage can be reduced since the masked region is not sampled from. An algorithm and a software package are developed for just such a calculation. Furthermore, differencing errors in the presence of discontinuous signals are utilized to produce the ‘Laplacian-difference’ method, which enhances pathological and discontinuous signals. Such signals, in the absence of systematics, might reveal the presence of cosmic defects. The scalar and pseudo-scalar fields produced will feature self-coupled modetransfer due to masking; the mode-transfer matrices are related to the optimal apodization schemes for extracting power spectra. The transfer matrices for various spectral operations on scalar fields are presented, which for the polarization spectra provide important computational advantages over the direct utilization of the E- and B-modes.
Supervisor: Jaffe, Andrew Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.542180  DOI: Not available
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