Exploring Non-Standard Extensions to the Standard Model of the Early Universe

Abstract

Recently, a hot topic of discussion has been the inconsistency between the values of some of the fundamental cosmological parameters derived from high-redshift cosmological probes such as the Planck measurements of the CMB and the low-redshift observations such as the cosmic ladder measurements. One possible explanation for this tension is that there is a problem with our current model of the early Universe, which leads to a discrepancy between the late-time and the early-time values of the fundamental parameters. In this thesis, we explore possible extensions to the Standard Model in two main sectors of cosmology, which can, in principle, account for some of the discordance. Motivated by the lack of a comprehensive neutrino theory, we first consider non-standard neutrino self-interactions and their effect on the power spectrum. We confirm and comment on the curious bimodal behavior already noted by several groups which suggests that current observations do not rule out non-standard neutrino self-interactions. The other topic we look into is the surface of last scattering. We explore the effect of its width on the power spectrum as well as the constraints we can get on it given the current precision of our data. We further study the dependence of its peak position on the physical scale and the implications this entails for observables such as the lensing kernel and the power spectrum.