The object of this thesis is to present various applications of the theory of cosmological perturbations. Within are contained a number of manuscripts, each concerned with a separate aspect of the theory. The thesis itself begins with a general overview of cosmological perturbation theory designed to be accessible to the non-specialist. Both the classical and quantum first order theory are considered. Back-reaction, via the formalism of the Effective Energy Momentum Tensor (EEMT) is reviewed. Subsequent chapters are more specialized dealing with various applications of the theory. At first order, topics discussed include the classicalization of cosmological perturbations (chapter 2), and the effects of including the dilaton and its fluctuations on a novel mechanism for the production of inhomogeneities in string gas cosmology (chapter 3). At second order, an original solution to the Dark Energy problem is proposed (chapter 4), and the effects of back-reaction on the power spectrum, including the spectral index and the gaussianity, are examined (chapter 5).

The Project in Canada to Search for Supersymmetric Objects (PICASSO) searches for cold dark matter through the direct detection of Weakly Interacting Massive Particles (WIMPs) via spin-dependent and spin independent interactions with 19F nuclei. The detection principle is based on the superheated droplet technique; the detectors consist of a gel matrix with millions of liquid droplets of superheated fluorocarbon (C4F10) dispersed in it. In order to reduce the background, it is essential to distinguish the signature of different background particles interacting in the detector. A dedicated setup was developed in order to study the response of the C4F10 droplets in the presence of different backgrounds. The main objectives of this research are to identify the actual size (diameter) of the droplet increases due to phase transition and to check and establish the correlation between the droplet size and the maximum amplitude of the signal. In addition, the alpha-neutron discrimination was studied by observing each event’s image frames and the associated acoustic signal to get the amplitude distribution. The mean ratio of bubble size to droplet size was found to be 5.48, independent of temperature and type of interacting particle. Furthermore, no correlation was found between the droplet size and the maximum amplitude of the signal. As for the discrimination studies, the analysis of the signal events has confirmed that alphas generated outside the active liquid in the gel are much more difficult to discriminate from neutron than when alphas are generated inside the active liquid.

Data from a new, wide field, coincident optical and X-ray survey, the X-ray Dark Cluster Survey (XDCS) are presented. The aim was to conduct simultaneous and independent searches for clusters of galaxies in the optical and X-ray passbands. Optical cluster detection algorithms implemented on the data are detailed. This resulted in catalogues of 185 I-band selected, 290 colour selected and 15 X-ray selected systems, residing in of optical + X-ray imaging. The relationship between optical (L(_E)) and X-ray luminosity (L(_x) ) was examined and found to exhibit significant scatter. This study highlights the higher efficiency and resolution of optical colour selection compared with other cluster detection methods. Spectroscopic redshifts confirmed the reality of a subsample of systems which were found with the optical algorithms, but required to have no detectable X-ray emission. These systems show comparable optical luminosity to the most X-ray luminous clusters, but orders of magnitude lower X-ray emission. This is consistent with the large scatter seen in the L(_x)-L(_e) relation. A near-infrared multicolour technique was explored and extended to search for high redshift (z>l) clusters. Finally, application of such techniques to forthcoming wide field near-infrared surveys was discussed and predictions for cluster finding in such surveys made.

No description available.

In this dissertation results are presented from a search for the pair production of heavy colored particles (gluinos, squarks) in R-parity conserving supersymmetric models, in which the lightest supersymmetric particle is a stable and neutral object. The search was performed for events with at least two tau leptons, two highly energetic jets and large missing transverse momentum in the final state on a data sample of proton-proton collisions at sqrt(s) = 7 TeV. The data sample was collected by the Compact Muon Solenoid detector at the Large Hadron Collider in 2011, and it corresponds to an integrated luminosity of 5fb^−1. The tau isolation variable was optimized for this search. The number of events corresponding to standard model processes in the final selection was estimated to be 7.49 ± 0.74 using background estimation techniques based on data. Nine observed events are found to be in agreement with the standard model prediction, and exclusion limits on gluino mass are obtained in the context of supersymmetric models at the 95% confidence level.

The Dark matter Experiment using Argon Pulse-shape discrimination will be a tonne scale liquid argon experiment to detect scintillation light produced by interactions with weakly interacting massive particles, leading dark matter candidates. The detector will be constructed out of acrylic and use a spherical array of 266 photo-multiplier tubes (PMTs) to count photons produced by an event and will use properties of liquid argon to discriminate signals from background events. There is currently a smaller prototype in operation underground at SNOLAB an underground laboratory in eastern Canada. The goal of the prototype detector is to understand the sources of background signals in a detector of our design and to validate our method of distinguishing different types of background radiation. The work presented herein is a series of studies with the common goal of understanding the source of background signals, and improving the resolution and efficiency of the detector.

The origin, nature and distribution of dark matter in the universe form some of the biggest questions in modern astrophysics. Dark matter is distributed on a wide range of scales in the universe. This thesis concentrates on galactic scales, attempting to lower the veil and probe the structure of dark matter in galaxies. (For complete abstract open document)

Thesis (Ph.D.) - University of St Andrews, September 2008.

Thesis (Ph. D.)--Florida State University, 2004. / Advisor: Dr. Howard Baer, Florida State University, College of Arts and Sciences, Dept. of Physics. Title and description from dissertation home page (viewed Sept. 24, 2004). Includes bibliographical references.

Thesis (Ph. D.)--Ohio State University, 2004. / Title from first page of PDF file. Document formatted into pages; contains xxi, 172 p.; also includes graphics (some col.) Includes bibliographical references (p. 162-172). Available online via OhioLINK's ETD Center