School of Physics - Theses

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Type: PhD thesis × Start date: 2020 × End date: 2022 × Author: Balkenhol, Lennart ×

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    Constraining cosmology with SPT-3G
    Balkenhol, Lennart ( 2022)
    Cosmic Microwave Background (CMB) observations are rich in cosmological information and a key pillar of modern cosmology. The South Pole Telescope offers a particularly clear view of the millimetre sky and its latest receiver, SPT-3G, facilitates unprecedented measurements of CMB anisotropies on small angular scales. In this thesis, we present measurements of the CMB temperature and polarisation power spectra using SPT-3G data recorded in 2018 covering a region of approximately 1500deg^2 in the southern sky. We also present the first comparison of covariance conditioning schemes for CMB data at the matrix- and the parameter-level. For empirical covariance estimators using less than or approximately 100 independent data realisations, moderate conditioning schemes can lead to an underestimation of the parameter error by up to a factor of 1.3 compared to the uncertainty inferred from the likelihood. These results inform the analysis SPT-3G data. We demonstrate the internal consistency of the SPT-3G 2018 temperature and polarisation band powers across frequency bands and spectra, and find excellent agreement. We present cosmological constraints using the polarisation spectra and report consistency with the standard model. We find H0 = 68.8 km/s/Mpc, which is considerably lower than the most precise local determination of the expansion rate. Cosmological constraints from SPT-3G and Planck data are in good agreement. We produce constraints using SPT-3G 2018 data alone and in combination with other data on a series of model extensions drawn from the following parameters: the effective number of neutrino species; the primordial helium abundance; the sum of neutrino masses; the mass of a sterile neutrino; the mean spatial curvature; the baryon clumping induced by primordial magnetic fields; the initial field value, critical redshift, and contribution to the energy density at the critical redshift of an early dark energy component. We discuss the constraints on each model in detail and report no statistically significant and robust preference for any of these extensions over the standard model.