PhD Dissertation- 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 radiation. However, the model has shown significant tension with an increasing set of measurements, ranging from measurements 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 construct 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, evidence that it ought to be seriously considered as the possible accurate descriptor of our Universe. Finally, I present a theoretical prediction of the number of z>6 blazars that will be detectible by upcoming surveys by the Square Kilometer Array (SKA). This prediction is entirely phenomenological, based on SED measurements of known blazars. The predictions for the number of blazars detectible by SKA are drastically different between these models such that upon the completion of the survey, either the Rh=ct universe or ΛCDM will be drastically preferred over the other.