Rogers, KK; (2018) A clear view of the primordial Universe. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Observations of temperature anisotropies in the cosmic microwave background (CMB) and measurements of the large-scale structure of matter have established the standard Lambda cold dark matter model of cosmology. Precise measurements of new observables will test extensions to the standard cosmological model, e.g., a non-zero tensor-to-scalar ratio of primordial perturbations, a running of the spectral index of the primordial power spectrum (both tests of cosmic inflation), or new components like massive neutrinos and warm dark matter (WDM). Two of the most promising observables to test these extensions in upcoming surveys are polarisation anisotropies in the CMB and correlations in the Lyman-alpha forest. Accurate cosmological parameter estimation, however, is only achievable through careful consideration of instrumental and astrophysical systematic effects, either by removing contamination in data or modelling its effect during statistical inference. I present new approaches to controlling contaminants to CMB temperature and polarisation and the Lyman-alpha forest. The primary contamination to the CMB is foreground Galactic radiation, e.g., synchrotron and thermal dust emission. I demonstrate the use of directional wavelets in more accurately reconstructing CMB temperature maps in the presence of these foregrounds, using Planck simulations and data. The complexity of polarised Galactic emissions limits constraints on inflation and neutrinos using CMB polarisation. I show how spin directional wavelets can allow additional morphological information to improve cosmic and foreground component separation. The Lyman-alpha forest probes the primordial power spectrum and the suppression of small-scale clustering by neutrinos or WDM. However, estimation of the shape of the power spectrum is biased by broadened absorption lines formed by high density systems of neutral hydrogen. I present models of their effect, built from Illustris cosmological hydrodynamical simulations. Being functions of absorber column density provides the flexibility to model residual contamination, after the largest absorbers have been removed from data.

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