In this thesis, we present three projects that describe the use of the XMM-Newton Cluster Survey (XCS) to investigate exotic astrophysical phenomena. Each project widens the scope of XCS beyond the study of cluster cosmology. In the first project, we derive correlations between X-ray properties of Active Galactic Nuclei (AGN) and mass of its Super Massive Black Hole (SMBH). These properties are the X-ray luminosity (LX) and a measure of the variability of the AGN - the normalised excess variance (σ2NXS). We confirm previous results indicating an anti-correlation between black hole mass (MBH) and σ2NXS, as well as anti-correlation between LX and σ2NXS, and a positive correlation between LX and MBH. We investigate whether there is a redshift evolution in these relations. We then develop methods to estimate MBH from short exposure X-ray observations specific to the eROSITA observatory, to allow us to measure LX of millions of AGN. The second project describes a new method to detect the rarest of X-ray transient sources, X-ray ashes (XRFs), through a serendipitous search of the XCS catalogue. We categorize the detected XRF candidates and look in more detail at one that is most likely to be an XRF. Based on its properties, we estimate an upper limit to their occurrence. A third project describes our method to search for an unknown emission line in the stacked spectra of galaxy clusters from the XCS extended source catalogue. This line, if found, may be evidence of a hypothetical particle - the sterile neutrino - which has been postulated as a candidate for dark matter. We review other research that has led to published work, as well as laying the foundation for future collaborations. This includes work on improving the XCS temperature pipeline in order to estimate the temperatures of galaxy clusters.

This dissertation explores two topics located in the intersection of quantum mechanics and cosmology. Entanglement harvesting is a phenomenon in which quantum entanglement can develop between the states of two Unruh-DeWitt detectors travelling through spacetime by way of mutual interaction with a scalar quantum field. I numerically explore entanglement harvesting of Unruh-DeWitt detectors in Minkowski space travelling with constant acceleration, generalizing previous analytical results which held only in a limiting case. Cosmic bubble collisions arise in inflationary cosmology as a mechanism to begin reheating at the end of inflation. I extend the previously proposed theory of boom and bust inflation which relies on the existence of a large extra dimension by exploring particular inflationary models in which reheating need not begin the first time that two bubble walls collide. This allows for a smaller lower bound on the size of the compact extra dimension in the boom and bust proposal.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Physics, 1982. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE / Vita. / Includes bibliographical references. / by Lawrence Maxwell Krauss. / Ph.D.

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1In this dissertation we work out in detail a new proposal to define rigorously a sector of loop quantum gravity at the diffeomorphism invariant level corresponding to homogeneous and isotropic cosmologies, and propose how to compare in detail the physics of this sector with that of loop quantum cosmology. The key technical steps we have completed are (a) to formulate conditions for homogeneity and isotropy in a diffeomorphism covariant way on the classical phase space of general relativity, and (b) to translate these conditions consistently using well-understood techniques to loop quantum gravity. To impose the symmetry at the quantum level, on both the connection and its conjugate momentum, the method used necessarily has similiarities to the Gupta-Bleuler method of quantizing the electromagnetic field. Lastly, a strategy for embedding states of loop quantum cosmology into this new homogeneous isotropic sector, and using this embedding to compare the physics, is presented. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2019. / FAU Electronic Theses and Dissertations Collection

In this dissertation we study the dynamics of loop quantum gravity and its applications. We propose a tunneling phenomenon of a black hole-white hole transition and derive an amplitude for such transition using the spinfoam framework. We investigate a special class of kinematical states for loop quantum gravity - Bell spin networks - and show that their entanglement entropy obeys the area law. We develop a new spinfoam vertex amplitude that has the correct semi-classical limit. We then apply this new amplitude to calculate the graviton propagator and a cosmological transition amplitude. The results of these calculations show feasibility of computations with the new amplitude and its viability as a spinfoam model. Finally, we use physical principles to radically constrain ambiguities in the cosmological dynamics and derive unique Hamiltonian dynamics for Friedmann-Robertson-Walker and Bianchi I cosmologies. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2019. / FAU Electronic Theses and Dissertations Collection

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Thesis (M. Div.)--Emmanuel School of Religion, 2004. / Vita. Includes bibliographical references (leaves 43-48).

Thesis (Ph. D.)--University of Notre Dame, 2005. / Includes bibliographical references (p. 420-436).