The Minimally Supersymmetric Standard Model (MSSM) provides us with a WIMP dark matter candidate particle, the neutralino. Neutralinos from the dark matter halo can potentially become captured by the sun and concentrated in the core, where they can undergo self-annihilation and so produce a distinct neutrino signal. The IceCube Neutrino Observatory has the potential to detect this neutrino signal and thus give indirect evidence of the presence and properties of neutralino dark matter. Although the full, unconstrained MSSM has 105 parameters this can be reduced to 25 parameters by the application of physically motivated assumptions. Scans of this MSSM-25 parameter space are conducted using the DarkSUSY software package and an adaptive scanning technique based on the Monte-Carlo VEGAS algorithm. The IceCube exclusion confidence level is then calculated for a set of points produced by these scans. Results indicate that the detection capability of IceCube exceeds that of current direct detection methods in certain regions of the parameter space. The use of a 25 dimensional parameter space reveals that there are new regions of observables with high exclusion confidence levels compared to earlier simulations performed with a seven dimensional parameter space.

This thesis studies the symmetries and phenomenologies of the massive vector fields of indefinite spin with both scalar and spin-one degrees of freedom and Elko. The investigation is conducted by using and extending the quantum field theory formalism developed by Wigner and Weinberg. In particular, we explore the possibility that the W± and Z bosons have an additional scalar degree of freedom and show that Elko is a fermionic dark matter candidate. We show that the massive vector fields of indefinite spin are consistent with Poincaré symmetry and have physically desirable properties that are absent for their pure spin-one counterpart. Using the new vector fields, the decay of the W± and Z bosons to leptons at tree-level are in agreement with the Standard Model (SM) predictions. For higher order scattering amplitudes, the theory has better convergent behaviour than the intermediate vector boson model and the Fermi theory. Elko has the unusual property that it satisfies the Klein-Gordon but not the Dirac equation and has mass dimension one instead of three-half. We show that the Elko fields are local only along a preferred axis and that they violate Lorentz symmetry. Motivated by the results obtained by Ahluwalia and Horvath that the Elko spin-sums are covariant under very special relativity (VSR) transformations, we derive the VSR particle states and quantum fields. We show that the VSR particles can only interact with the SM particles through gravity and massive scalar particles thus making them and hence Elko dark matter candidates.

Well motivated theoretical models predict the annihilation of dark matter (DM) into standard model particles, a phenomenon which could be a significant source of photons in the gamma-ray sky. With its unprecedented sensitivity and its broad energy range (20 MeV to more than 300 GeV) the main instrument on board the Fermi satellite, the Large Area Telescope (LAT), might be able to detect an indirect signature of DM annihilations. In this work we revisit several interesting claims of extended dark matter emission made from analyses of Fermi-LAT data: First, based on three years of Fermi Large Area Telescope (LAT) gamma-ray data of the Virgo cluster, evidence for an extended emission associated with dark matter pair annihilation in the bb̄ channel has been reported by Han et al. (arxiv:1201.1003). After an in depth spatial and temporal analysis, we argue that the tentative evidence for a gamma-ray excess from the Virgo cluster is mainly due to the appearance of a population of previously unresolved gamma-ray point sources in the region of interest. These point sources are not part of the LAT second source catalogue (2FGL), but are found to be above the standard detection significance threshold when three or more years of LAT data is included. Second, we confirm the detection of a spatially extended excess of 2-5 GeV gamma rays from the Galactic Center (GC), consistent with the emission expected from annihilating dark matter or an unresolved population of about 10³ milisecond pulsars. However, there are significant uncertainties in the diffuse galactic background at the GC. We have performed a revaluation of these two models for the extended gamma ray source at the GC by accounting for the systematic uncertainties of the Galactic diffuse emission model. We also marginalize over point source and diffuse background parameters in the region of interest. We show that the excess emission is significantly more extended than a point source. We find that the DM (or pulsars population) signal is larger than the systematic errors and therefore proceed to determine the sectors of parameter space that provide an acceptable fit to the data. We found that a population of order a 10³ MSPs with parameters consistent with the average spectral shape of Fermi-LAT measured MSPs was able to fit the GC excess emission. For DM, we found that a pure τ⁺τ⁻ annihilation channel is not a good fit to the data. But a mixture of τ⁻τ⁻ and bb̄ with a (σν) of order the thermal relic value and a DM mass of around 20 to 60 GeV provides an adequate fit. We also consider the possibility that the GeV excess is due to nonthermal bremsstrahlung produced by a population of electrons interacting with neutral gas in molecular clouds. The millisecond pulsars and dark matter alternatives have spatial templates well fitted by the square of a generalized Navarro-Frenk-White (NFW) profile with inner slope γ = 1.2. We model the third option with a 20-cm continuum emission Galactic Ridge template. A template based on the HESS residuals is shown to give similar results. The gamma-ray excess is found to be best fit by a combination of the generalized NFW squared template and a Galactic Ridge template. We also find the spectra of each template is not significantly affected in the combined fit and is consistent with previous single template fits. That is, the generalized NFW squared spectrum can be fit by either of order 10³ unresolved MSPs or DM with mass around 30 GeV, a thermal cross section, and mainly annihilating to bb̄ quarks. While the Galactic Ridge continues to have a spectrum consistent with a population of nonthermal electrons whose spectrum also provides a good fit to synchrotron emission measurements. We also show that the current DM fit may be hard to test, even with 10 years of Fermi-LAT data, especially if there is a mixture of DM and MSPs contributing to the signal, in which case the implied DM cross section will be suppressed.

In this study I present two N-body computer simulations of the Bullet Cluster (1E 0657-56) merging system. The models are fully self-consistent, meaning that all gravitational forces are determined by the distribution of the particles. Initial positions and velocities of the two clusters are determined by solving a two-body problem. Post-collision time period shows an increase in the line-of-sight velocity dispersion in both clusters, and is consistent with previous Bullet Cluster studies. I also investigate the temporal evolution of the average cluster radial velocities of the galaxies located in the inner, middle, and outer regions of the clusters. I show that the orbital trajectories differ in pre- and post-collision periods. Inner region galaxies receive an impulse that moves them outward from the cluster center immediately after collision, while at the same time the outer region galaxies are pulled back towards the cluster center. / Department of Physics and Astronomy

Current models of cosmology and galaxy formation are possibly at odds with observations of small-scale galaxies. Such is the case for the dwarf spheroidal (dSph) galaxies of the Milky Way (MW), where tension exists in explaining their observed abundance, mass, and internal structure. Here we present an analysis of the substructure surrounding MW-sized haloes in a Lambda Cold Dark Matter (LCDM) simulation suite. Combined with a semi-analytic model of galaxy formation and evolution, we identify substructures that are expected to host dSph galaxies similar to the satellites of the MW. We subsequently use these simulations to investigate the orbital properties of dSph satellite galaxies to make contact with those orbiting the MW. After accretion into the main halo, the higher mass ``luminous'' substructure remains on highly radial orbits while the orbits of lower mass substructure, which are not expected to host stars, tend to scatter off of the luminous substructure, and thus circularize over time. The orbital ellipticity distribution of the luminous substructure shows little dependence on the mass or formation history of the main halo, making this distribution a robust prediction of LCDM. Through comparison with the ellipticity distribution computed from the positions and velocities of the nine MW dSph galaxies that currently have proper motion estimates as a function of the assumed MW mass, we present a novel means of estimating the virial mass of the Milky Way. The best match is obtained assuming a mass of 1.1 x 10^12 M_sun with 95 per cent confidence limits of (0.6 - 3.1) x 10^12 M_sun. The uncertainty in this estimate is dominated by the large uncertainties in the proper motions and small number of MW satellites used, and will improve significantly with better proper motion measurements from Gaia. We also measure the shape of the gravitational potential of subhaloes likely to host dSphs, down to radii comparable to the half-light radii of MW dSphs. Field haloes are triaxial in general, while satellite haloes become more spherical over time due to tidal interactions with the host. Thus through the determination of the shape of a MW dSph's gravitational potential via line of sight velocity measurements, one could in principle deduce the impact of past tidal interactions with the MW, and thus determine its dynamical history. Additionally, luminous subhaloes experience a radial alignment of their major axes with the direction to the host halo over time, caused by tidal torquing with the host's gravitational potential during close pericentric passages. This effect is seen at all radii, even down to the half-light radii of the satellites. Radial alignment must be taken into account when calibrating weak-lensing surveys which often assume isotropic orientations of satellite galaxies surrounding host galaxies and clusters. / Graduate / 0606

Current models of cosmology and galaxy formation are possibly at odds with observations of small-scale galaxies. Such is the case for the dwarf spheroidal (dSph) galaxies of the Milky Way (MW), where tension exists in explaining their observed abundance, mass, and internal structure. Here we present an analysis of the substructure surrounding MW-sized haloes in a Lambda Cold Dark Matter (LCDM) simulation suite. Combined with a semi-analytic model of galaxy formation and evolution, we identify substructures that are expected to host dSph galaxies similar to the satellites of the MW. We subsequently use these simulations to investigate the orbital properties of dSph satellite galaxies to make contact with those orbiting the MW. After accretion into the main halo, the higher mass ``luminous'' substructure remains on highly radial orbits while the orbits of lower mass substructure, which are not expected to host stars, tend to scatter off of the luminous substructure, and thus circularize over time. The orbital ellipticity distribution of the luminous substructure shows little dependence on the mass or formation history of the main halo, making this distribution a robust prediction of LCDM. Through comparison with the ellipticity distribution computed from the positions and velocities of the nine MW dSph galaxies that currently have proper motion estimates as a function of the assumed MW mass, we present a novel means of estimating the virial mass of the Milky Way. The best match is obtained assuming a mass of 1.1 x 10^12 M_sun with 95 per cent confidence limits of (0.6 - 3.1) x 10^12 M_sun. The uncertainty in this estimate is dominated by the large uncertainties in the proper motions and small number of MW satellites used, and will improve significantly with better proper motion measurements from Gaia. We also measure the shape of the gravitational potential of subhaloes likely to host dSphs, down to radii comparable to the half-light radii of MW dSphs. Field haloes are triaxial in general, while satellite haloes become more spherical over time due to tidal interactions with the host. Thus through the determination of the shape of a MW dSph's gravitational potential via line of sight velocity measurements, one could in principle deduce the impact of past tidal interactions with the MW, and thus determine its dynamical history. Additionally, luminous subhaloes experience a radial alignment of their major axes with the direction to the host halo over time, caused by tidal torquing with the host's gravitational potential during close pericentric passages. This effect is seen at all radii, even down to the half-light radii of the satellites. Radial alignment must be taken into account when calibrating weak-lensing surveys which often assume isotropic orientations of satellite galaxies surrounding host galaxies and clusters. / Graduate / 0606

Inorganic scintillators are playing an ever increasing role in the search for rare events. Progress in the use of cryogenic phonon-scintillation detectors (CPSD) has allowed for a rapid increase in sensitivity and resolution of experiments using this technique. It is likely that CPSD will be used in future dark matter searches with multiple scintillator materials. Further improvements in the performance of CPSD can be expected if the amount of light collected is increased. In this thesis, two approaches are used to look at ways of maximising the amount of light collected in CPSD modules. The first approach is to obtain a detailed understanding of the spectroscopic properties in the crystal to identify ways of increasing their scintillation intensity. The second is to simulate the light collection properties using a Monte-Carlo simulation program. This requires a detailed understanding of the optical properties of inorganic scintillators and obtaining this information is the focus of the current work. Two new methods have been developed to evaluate the scintillation decay time and the intrinsic light yield of scintillators. These methods are tested on CRESST CaWO₄ crystals so that all the input parameters necessary for the simulation of CRESST modules is available. These input parameters are used to successfully explain features of the light collection in CRESST CPSD modules and to suggest possible improvements to the design of the modules. In summary, the current work has contributed to the development of a standardised method to maximise the light yield that can be obtained from CPSD for application to rare event searches.

The aim of this project was to explore the shapes of dark matter halos using high resolution N-body simulations. One of the main aspects explored was how well the shape can be measured through weak lensing. To explore this, simulations were run using the GADGET-2 code \cite{SPRING05} and a method used to measure ellipticities was tested \cite{oguri1}. It was found that Large Scale Structure along the line of sight diluted the measurements and made halos appear more spherical. On the other hand, substructure close to the halo introduced a bias where intrinsically elliptical halos appeared to be slightly more spherical and intrinsically spherical halos appeared to be slightly more elliptical. The effects of projection on concentration were also explored, it was concluded that halos which are most elliptical in 3D tend to appear the most concentrated in projection. Finally, we tested the possibility of using shape or concentration measurements to help break the degeneracy in $\Omega_M$ and $\sigma_8$. We found that this may be possible with $\sim$ 3000-4000 shape measurements or $\sim$ 400-500 concentration measurements.

A variety of precision observations suggest that the present universe is dominated by some unknown components, the so-called dark matter and dark energy. The distribution and properties of these components are the focus of modern cosmology and we are only beginning to understand them. Gravitational lensing, the bending of light in the gravitational field of a massive object, is one of the predictions of the general theory of relativity. It has become an ever more important tool for investigating the dark universe, especially with recent and coming advances in observational data. This thesis studies gravitational lensing effects on scales ranging over ten orders of magnitude to probe very different aspects of the dark universe. Implementing a matter distribution following the predictions of recent simulations, we show that microlensing by a large population of massive compact halo objects (MACHOs) is unlikely to be the source of the observed long-term variability in quasars. We study the feasibility of detecting the so far elusive galactic dark matter substructures, the so-called “missing satellites”, via millilensing in galaxies close to the line-of-sight to distant light sources. Finally, we utilise massive galaxy clusters, some of the largest structures known in the universe, as gravitational telescopes in order to detect distant supernovae, thereby gaining insight into the expansion history of the universe. We also show, how such observations can be used to put constraints on the dark matter component of these galaxy clusters. / At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 6: Submitted.

Thesis (Ph. D.)--Ohio State University, 2008. / Title from first page of PDF file. Includes bibliographical references (p. 160-175).