Topics in early and late Universe cosmology
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In this thesis, we explore different problems in various areas of cosmology. The inflationary paradigm has been very successful in explaining cosmological observations. However, some problems still linger on. In the first part of the thesis, we investigated the evolution of perturbations in an alternative bouncing scenario described by cuscuton gravity. We first derived the formulation describing the evolution of perturbation in cuscuton gravity. Then, using a toy model, we showed that unlike other bouncing scenarios, it is possible to have a regular bouncing scenario without catastrophic instabilities in cuscuton gravity. In the second part of the thesis, we investigate the peculiar velocity field in the local Universe using observational data. We study two aspects of the local peculiar velocity field. First, by comparing the reconstructed velocity field with the observations, we constrained the cosmological parameter combination, fσ8. We also compiled the largest peculiar velocity catalog based on low redshift Type Ia supernovae. Using an extended forward-likelihood method that self-consistently calibrates the distance indicator relationship, we find fσ8 = 0.400 ± 0.017. The peculiar velocity field in the local Universe is also useful for correcting redshifts of galaxies for measuring the Hubble constant and distances to galaxies. We compare some of the commonly-used peculiar velocity models of the local Universe. By comparing the various peculiar velocity models to additional peculiar velocity observations, we show that reconstruction-based velocity field performs better than kernel-smoothed peculiar velocity fields. In the final part of the thesis, we describe a new statistical method of constraining H0 standard sirens. Our method relies on using a reconstructed density field. Using a mock simulation, we show that our method gives an unbiased estimate of H0. We also infer H0 using this method for the GW170817 data.
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Supranta Sarma Boruah (2020). Topics in early and late Universe cosmology. UWSpace. http://hdl.handle.net/10012/16111