A Survey of Results in Modern Precision Cosmology

Citation

Pullen, Anthony Robert (2011) A Survey of Results in Modern Precision Cosmology. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/VJ9N-0J70. https://resolver.caltech.edu/CaltechTHESIS:05042011-123721947

Abstract

In this work, we evaluate the evidence for some of the more exotic ideas in cosmology for which scientists are searching today, these anomalies being dark matter, statistical anisotropy, and non-Gaussianity. Dark matter, which is estimated to comprise 83% of the matter in our universe, still remains undiscovered. We search data from the Energetic Gamma Ray Experiment Telescope for a gamma-ray line in the energy range 0.1-10 GeV from the 10X10 degree region around the Galactic center. Our null results lead to upper limits to the line flux from the Galactic center. We use these limits to place constraints on the particle's two-photon annihilation cross section as a function of its mass, which we show to produce stronger limits than those derived from measurements of the 511-keV line.

Next, we investigate the possibility that cosmic inflation deviates from statistical isotropy. Statistical isotropy is a common assumption that should be tested. We develop cosmic-microwave-background statistics for a direction-dependent primordial power spectrum. We then construct minimum-variance estimators for the coefficients of a spherical-harmonic expansion of the direction-dependence of the primordial power spectrum. We find that a power quadrupole as small as 2.0% can be detected by the Planck satellite. We also constrain statistical anisotropy of the quadrupolar form using a sample of photometric luminous red galaxies measured by the Sloan Digital Sky Survey. Not detecting evidence, we place limits on an axisymmetric quadrupole model. We find discrepancies between our results and a cosmic microwave background analysis that claimed a positive detection. We also find the quadrupolar asymmetry limits to be between -0.41 and 0.38 with 95% probability.

Finally, we prepare a search for evidence of non-Gaussianity in the the early universe. Scale-dependent bias has been shown to be a competitive probe of non-Gaussianity in large-scale structure, and constraints have been calculated using various tracers of the matter distribution. We seek to extend this analysis to the latest sample of photometric quasars measured by the Sloan Digital Sky Survey to search for evidence of scale-dependent bias in large-scale structure. Specifically we construct three data samples at various redshifts, removing various systematic effects. We calculate the cross-correlation angular power spectra between two of the data samples to search for any remaining systematics. We find a positive detection on large scales, which leads us to the conclusion that more systematics testing is needed to render this QSO catalog useful to constrain non-Gaussianity.

Thesis Files