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.

Although exotic objects like supermassive black holes (SMBHs) and dark matter halos do not emit or interact with light, we can still detect them across the vastness of space. By observing the gravitational dance of objects we can see, astronomers are able to infer the mass of the invisible objects they orbit. This has led to the discovery that nearly every massive galaxy hosts a SMBH at its center, and has confirmed that every galaxy is embedded in an extended halo of dark matter. However, the practice of inferring mass from the motions of bright kinematics tracers has many complications, not the least of which is that we seldom observe more than the line-of-sight component of the instantaneous velocity of a star. Consequently, astronomers must build dynamical models of the galaxies they wish to study. These models often rely on overly restrictive assumptions, or are crippled by degeneracies amongst their parameters and lack predictive power. In this thesis, I introduce a significant advancement into the field of dynamical modeling. My modeling technique is based on the powerful principle of orbit superposition, also known as Schwarzschild Modeling. This technique is robust to many of the degeneracies associated with dynamical modeling, and has enjoyed much success in measuring the SMBHs and dark matter halos of large elliptical or bulge-dominated galaxies. I use it in Chapter 2 to accurately measure the SMBH in the Sombrero Galaxy (NGC 4594) and to constrain its dark matter halo. Unfortunately, when measuring dark matter halos with Schwarzschild Modeling, the modeler is required to adopt a parameterization for the dark matter density profile. Often this is precisely the quantity one wishes to measure. To avoid this reliance on a priori parameterizations, I introduce a technique that calculates the profile non-parametrically. Armed with this powerful new technique, I set out to measure the distribution of dark matter in the halos of some of the smallest galaxies in the Universe. These dwarf spheroidal galaxies (dSphs) orbit the Milky Way as satellites, and their dark matter content has been studied extensively. However, the models used to probe their halos have been simplistic and required overly restrictive assumptions. As a result, robust conclusions about their dark matter content have remained elusive. Into this controversial and active area of study, I bring Non-Parametric Schwarzschild Modeling. The results I find offer the most robust and detailed measurements of the dark matter profiles in the dSphs to date. I begin my study with the first application of standard Schwarzschild Modeling to any dSph galaxy by using it in Chapter 3 on Fornax. This chapter details the process of re-tooling Schwarzschild Modeling for the purpose of measuring these small galaxies. In Chapter 4, I introduce the fully non-parametric technique, and apply it to Draco as proof of concept. Chapter 5 presents the main results of this thesis. Here I apply Non-Parametric Schwarzschild Modeling to Draco, Carina, Fornax, Sculptor, and Sextans. By relaxing the assumption of a parameterization for the dark matter profile, I find a variety of profile types in these five galaxies---some of which are consistent with past observations, others consistent with predictions from simulations, and still others were completely unanticipated. Finally, in Chapter 6 I describe the modeling of these galaxies in more detail. I demonstrate the accuracy of Non-Parametric Schwarzschild Modeling by recovering a known dark matter profile from artificial simulated data. I also expound upon the modeling results by presenting the detailed orbit structure of the five dSphs. Lastly, I compare my results to hydrodynamical simulations to explore the link between dark matter profile type and the baryon content of the dSphs. / text

Galaxy clusters are the most massive bound systems known in the Universe and are believed to have formed through large scale structure formation. They host relativistic cosmic-ray (CR) populations and are gravitationally bound by large amounts of Dark Matter (DM), both providing conditions in which high-energy gamma rays may be produced either via CR interactions with the intracluster medium or through the annihilation or decay of DM particles. Prior to the launch of the Fermi satellite, predictions were optimistic that these sources would be established as γ-ray-bright objects by observations through its prime instrument, the Large Area Telescope (LAT). Yet, despite numerous efforts, even a single firm cluster detection is still pending. This thesis presents a number of studies based on data taken by the LAT over its now seven year mission aiming to discover these γ rays. Using a joint likelihood technique, we study the γ-ray spectra of a sample of nearby clusters searching for a CR-induced signal due to hadronic interactions in the intracluster medium. While we find excesses in some individual targets, we attribute none to the cluster. Hence, we constrain the maximum injection efficiency of hadrons being accelerated in structure formation shocks and the fraction of CR-to-thermal pressure. We also perform a refined search targeting the Coma cluster specifically due to its large variety of existing observations in other wavebands. In the latter case we find weak indications of an excess which however falls below the detection threshold. Because the cluster emission we consider is inherently extended, we need to take into account the imperfect modeling of the foreground emission, which may be particularly difficult such as is the case with the Virgo cluster. Here, we assess the systematics associated with the foreground uncertainties and derive limits based on an improved background model of the region. For the first time we derive limits on the γ-ray flux from CR and DM-interactions in which we take into account the dynamical state of the system. For DM we also include the contribution from substructure. The DM domain is further explored by searching for line-like features as they arise from the annihilation of DM into two photons in a large sample of clusters, including Virgo and Coma. Finding no evidence for γ-ray lines, we derive limits on the DM annihilation cross section that are roughly a factor 10 (100) above that derived from observations of the galactic center assuming an optimistic (conservative) scenario regarding the boost due to DM substructure. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Submitted. Paper 4: Submitted.</p>

Massive gravity is an extension of general relativity where the graviton, which mediates gravitational interactions, has a non-vanishing mass. The first steps towards formulating a theory of massive gravity were made by Fierz and Pauli in 1939, but it took another 70 years until a consistent theory of massive gravity was written down. This thesis investigates the phenomenological implications of this theory, when applied to cosmology. In particular, we look at cosmic expansion histories, structure formation, integrated Sachs-Wolfe effect and weak lensing, and put constraints on the allowed parameter range of the theory. This is done by using data from supernovae, the cosmic microwave background, baryonic acoustic oscillations, galaxy and quasar maps and galactic lensing. The theory is shown to yield both cosmic expansion histories, galactic lensing and an integrated Sachs-Wolfe effect consistent with observations. For the structure formation, however, we show that for certain parameters of the theory there exists a tension between consistency relations for the background and stability properties of the perturbations. We also show that a background expansion equivalent to that of general relativity does not necessarily mean that the perturbations have to evolve in the same way. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 5: Manuscript. Paper 6: Manuscript.</p>

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No description available.

The topic of this thesis is about cosmic inflations, including the early-universe inflation that seeds the initial inhomogeneities of our universe, and the late-time cosmic acceleration triggered by dark energy. The two inflationary epochs have now become part of the standard $\Lambda$CDM cosmological model. In the standard paradigm, dark energy is a cosmological constant or vacuum energy, while the early-universe inflation is driven by a slowly rolling scalar field. Currently the minimal $\Lambda$CDM model with six parameters agrees well with cosmological observations. If the greatest achievement of the last twenty golden years of cosmology is the $\Lambda$CDM model, the theme of future precision cosmology will be to search for deviations from the minimal $\Lambda$CDM paradigm. It is in fact expected that the upcoming breakthroughs of cosmology will be achieved by observing the subdominant anomalies, such as non-Gaussianities in the Cosmic Microwave Background map. The aim of this thesis is then to make theoretical predictions from models beyond $\Lambda$CDM, and confront them with cosmological observations. These models include: 1) a new dark energy parametrization based on quintessence models; 2) reconstructing early-universe inflationary trajectories, going beyond the slow-roll assumption; 3) non-Gaussian curvature fluctuations from preheating after the early-universe inflation; 4) infra-red cascading produced by particle production during inflation; 5) preheating after Modular inflation; 6) decaying cold dark matter. We update the cosmological data sets -- Cosmic Microwave Background, Type Ia supernova, weak gravitational lensing, galaxy power spectra, and Lyman-$\alpha$ forest -- to the most current catalog, and run Monte Carlo Markov Chain calculations to obtain the likelihood of parameters. We also simulate mock data to forecast future observational constraints.

The topic of this thesis is about cosmic inflations, including the early-universe inflation that seeds the initial inhomogeneities of our universe, and the late-time cosmic acceleration triggered by dark energy. The two inflationary epochs have now become part of the standard $\Lambda$CDM cosmological model. In the standard paradigm, dark energy is a cosmological constant or vacuum energy, while the early-universe inflation is driven by a slowly rolling scalar field. Currently the minimal $\Lambda$CDM model with six parameters agrees well with cosmological observations. If the greatest achievement of the last twenty golden years of cosmology is the $\Lambda$CDM model, the theme of future precision cosmology will be to search for deviations from the minimal $\Lambda$CDM paradigm. It is in fact expected that the upcoming breakthroughs of cosmology will be achieved by observing the subdominant anomalies, such as non-Gaussianities in the Cosmic Microwave Background map. The aim of this thesis is then to make theoretical predictions from models beyond $\Lambda$CDM, and confront them with cosmological observations. These models include: 1) a new dark energy parametrization based on quintessence models; 2) reconstructing early-universe inflationary trajectories, going beyond the slow-roll assumption; 3) non-Gaussian curvature fluctuations from preheating after the early-universe inflation; 4) infra-red cascading produced by particle production during inflation; 5) preheating after Modular inflation; 6) decaying cold dark matter. We update the cosmological data sets -- Cosmic Microwave Background, Type Ia supernova, weak gravitational lensing, galaxy power spectra, and Lyman-$\alpha$ forest -- to the most current catalog, and run Monte Carlo Markov Chain calculations to obtain the likelihood of parameters. We also simulate mock data to forecast future observational constraints.

In this work the search for the dark matter arising from a model of extra dimensions, otherwise known as Kaluza Klein WIMPs, on the data taken with the AMANDA neutrino telescope in the South Pole is presented. The limit on the dark matter from the Kaluza Klein Solar WIMPs analysis on the data taken from year 2001 to 2003 is derived.

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.