Observational and Theoretical Cosmology with Novel Statistical Methods

Abstract

The standard ΛCDM model of the universe has been shown to be consistent with a wide range of astronomical observations, including many properties of the cosmic microwave background (CMB). However, the model has significant tension with an increasing set of measurements, ranging from determinations of the Hubble Constant to the angular correlation function of the CMB. This motivates revisions to ΛCDM, or the consideration of alternative models (or even entirely new physics). The Rh=ct universe is an alternative FLRW cosmology that has thus far performed very well in describing a wide range of astronomical observations. In this dissertation, I present a sequence of tests of cosmology. These tests are designed to determine whether the Rh=ct universe performs better than the standard model in accounting for the considered data. First, I show the development of a two-point diagnostic to compare a model’s predictions with observations. This diagnostic is applied to passively evolving elliptical galaxies (cosmic chronometers) and the Hubble diagram as constructed using HII galaxies. Second, I make use of relative likelihoods with strongly-lensed galaxies to constrain standard ΛCDM and an alternative dark matter parameterization (wCDM). These model fits are then compared with the Rh=ct universe by means of several information criteria. Each of the direct comparisons using existing data favor the Rh=ct universe over standard ΛCDM to different degrees, warranting further research to determine whether it accurately describes the Universe. Finally, I present a theoretical prediction of the number of z>6 blazars that will be detectable by upcoming surveys by the Square Kilometer Array (SKA). This prediction is entirely phenomenological, based on spectral energy distribution (SED) measurements of known blazars. The predictions for the number of blazars detectable by SKA between these models are incompatible, such that either the Rh=ct universe or ΛCDM will be strongly preferred by the surveys.