| Summary: | The Cosmic Microwave Background (CMB) radiation, photons free-streaming from their last scattering surface at redshift around 1090, is currently our main source of information about the origin and history of the Universe. The vast recent advancement in technology has led to new possibilities for gathering data especially detecting the CMB with high accuracy. The goal of the two projects studied in this thesis is to improve the cosmological perturbation theory to better test cosmology with the upcoming data.
In chapter 4 we explore the effect of Rayleigh scattering on the CMB and cosmic structure. During and after recombination, in addition to Thomson scattering with free electrons, photons also coupled to neutral hydrogen and helium atoms through Rayleigh scattering. The frequency-dependence of the Rayleigh cross section breaks the thermal nature of CMB temperature and polarization anisotropies and effectively doubles the number of variables needed to describe CMB intensity and polarization statistics, while the additional atomic coupling changes the matter distribution and the lensing of the CMB. We introduce a new method to capture the effects of Rayleigh scattering on cosmological power spectra. We show the Rayleigh signal, especially the cross-spectra between the thermal (Rayleigh) E-polarization and Rayleigh (thermal) intensity signal, may be detectable with future CMB missions even in the presence of foregrounds, and how this new information might help to better constrain the cosmological parameters.
In chapter 5 we study the Cosmic Neutrino Background (CNB). In addition to the CMB, the standard cosmological model also predicts that neutrinos were decoupled from the rest of the cosmic plasma when the age of the Universe was less than one second, far earlier than the photons. We study the anisotropy of the CNB and for the first time present the full CNB anisotropy power spectrum at large and small scales both for a massless and massive neutrinos. We also show that how presence of nonstandard neutrino self-interactions compatible with current cosmological data alters the CNB power spectrum. === Science, Faculty of === Physics and Astronomy, Department of === Graduate
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