We present cosmological constraints from the Dark Energy Survey (DES) using a combined analysis of angular clustering of red galaxies and their cross-correlation with weak gravitational lensing of background galaxies. We use a 139 deg(2) contiguous patch of DES data from the Science Verification (SV) period of observations. Using large-scale measurements, we constrain the matter density of the Universe as Omega(m) = 0.31 +/- 0.09 and the clustering amplitude of the matter power spectrum as sigma(8) = 0.74 +/- 0.13 after marginalizing over seven nuisance parameters and three additional cosmological parameters. This translates into S-8 = sigma(8)(Omega(m)/0.3)(0.16) = 0.74 +/- 0.12 for our fiducial lens redshift bin at 0.35 < z < 0.5, while S-8 = 0.78 +/- 0.09 using two bins over the range 0.2 < z < 0.5. We study the robustness of the results under changes in the data vectors, modelling and systematics treatment, including photometric redshift and shear calibration uncertainties, and find consistency in the derived cosmological parameters. We show that our results are consistent with previous cosmological analyses from DES and other data sets and conclude with a joint analysis of DES angular clustering and galaxy-galaxy lensing with Planck Cosmic Microwave Background data, baryon accoustic oscillations and Supernova Type Ia measurements.

>Magister Scientiae - MSc / The Cosmological Principle forms part of one of the most fundamental hypotheses of modern Cosmology. So it is very important to assess whether it holds true using observational data, or whether it consists of a mathematical simplification. We probe the statistical isotropy of the Universe using the existing radio continuum data, by means of a local variance estimator. In order to investigate this, we analyse the number count variance of the radio catalog by looking at patches of approximately 10, 15, 20 & 25 degrees in radii, and thus comparing it to mock catalogs which reproduce the matter density power spectrum, as well as the same sky coverage of the real data. We establish criteria for accepting patches that have more than 90%, 70% & 50% of their pixels not masked. We make use of the NRAO VLA Sky Survey (NVSS), whose operational frequency is 1.4 GHz. We perform statistical tests for detecting possible departures from statistical isotropy using galaxy number counts with flux limits of 20 < SNVSS < 1000 mJy. We also compare the real data to the mock catalogs of the radio data in order to assess the statistical significance of our results. We use the local variance estimator for testing the statistical isotropy of our data sample. We find that the statistical properties of our sample are in reasonable agreement with the standard cosmological model. The mean of the distribution for the data falls well within the 95% confidence interval of the average of the simulated mocks. For all the radii and acceptance criteria for the patches, we found no significant deviations beyond those allowed by the standard model. As expected there were no large discrepancies between our mocks and the data. The results are consistent with statistical isotropy.

Les prédictions d'inflation du spectre de puissance de la perturbation de la courbure ont déjà fait l’objet de vérification d’un excellent niveau, permettant à de nombreux modèles de rester compatibles avec les observations. Dans la présente thèse, nous avons étudié les corrélations de troisième ordre qui pourraient permettre de mieux distinguer les différents modèles d'inflation les uns des autres. Parmi toutes les extensions possibles du modèle standard d'inflation, nous avons choisi d'étudier des modèles de deux champs scalaires à termes cinétiques standards et à métrique des champs plat. La nouveauté introduite par ces modèles est la présence de la perturbation d'isocourbure. Son interaction avec la perturbation adiabatique hors de l'horizon produit des non-linéarités caractéristiques des modèles à plusieurs champs scalaires. Dans, ce contexte, nous avons établi la forme de la perturbation adiabatique et de la perturbation d'isocourbure invariant sous transformations de jauge en deuxième ordre. De plus, nous avons trouvé l'action de troisième ordre qui décrit leurs interactions. En outre, nous avons élaboré le formalisme des grandes longueurs d'onde afin d'obtenir une expression pour le paramètre de non-gaussiannité fNL en fonction du potentiel des champs. Nous avons ensuite, utilisé cette formule pour traiter analytiquement - avec l'hypothèse de slow-roll - des classes générales de potentiels et vérifier nos résultats numériquement par la théorie exacte. De là, nous avons pu tirer des conclusions générales concernant les propriétés de fNL, comme par exemple la dépendance de sa magnitude des caractéristiques du trajet des champs et de la perturbation d'isocourbure, ainsi que sa dépendance de la magnitude et de la taille relative des trois impulsions dont le corrélateur à trois points est fonction. / Inflationary predictions for the power spectrum of the curvature perturbation have been verified to an excellent degree, leaving many models compatible with observations. In this thesis we studied third-order correlations, that might allow one to further distinguish between inflationary models. From all the possible extensions of the standard inflationary model, we chose to study two-field models with canonical kinetic terms and flat field space. The new feature is the presence of the so-called isocurvature perturbation. Its interplay with the adiabatic perturbation outside the horizon gives birth to non-linearities characteristic of multiple-field models. In this context, we established the second-order gauge-invariant form of the adiabatic and isocurvature perturbation and found the third-order action that describes their interactions. Furthermore, we built on and elaborated the long-wavelength formalism in order to acquire an expression for the parameter of non-Gaussianity fNL as a function of the potential of the fields. We next used this formula to study analytically, within the slow-roll hypothesis, general classes of potentials and verified our results numerically for the exact theory. From this study, we deduced general conclusions about the properties of fNL, its magnitude depending on the characteristics of the field trajectory and the isocurvature component, as well as its dependence on the magnitude and relative size of the three momenta of which the three-point correlator is a function.

Galaxy clusters are the most massive collapsed structures in the Universe and their properties offer a crucial insight into the formation of structure. High quality observational data is forthcoming with ongoing and upcoming surveys, but simulations are needed to provide robust theoretical predictions for comparison, as well mock data for testing observational techniques. Numerical simulations are now able to accurately model a range of astrophysical processes. This is highlighted in the BAHAMAS and MACSIS simulations, which have successfully reproduced the observed scaling relations of galaxy clusters. We use these simulations to quantify the impact baryons have on the mass distribution within galaxy clusters, as well as the bias in X-ray and weak lensing mass estimates. It is shown that baryons have only a minor affect on the spins, shape and density profiles of galaxy clusters and they have no significant impact on the bias in weak lensing mass estimates. When using spectroscopic temperatures and densities, the X-ray hydrostatic mass bias decreases as a function of mass, leading to a bias of ~40% for clusters with M_500 > 10^15 solar masses. In the penultimate chapter, we use the EAGLE and C-EAGLE simulations to construct more realistic mock cluster observations. The EAGLE simulations have been shown to successfully reproduce the properties of field galaxies and they are complemented by the C-EAGLE project, which extends this work to the cluster scale. We use these simulations to construct a cluster lightcone that accounts for the impact of uncorrelated large scale structure on cluster observables, including weak lensing mass estimates, the Sunyaev-Zel'dovich parameter and X-ray luminosity.

One of the most pressing, modern cosmological mysteries is the cause of the accelerated expansion of the universe. The energy density required to cause this large scale opposition to gravity is known to be both far in excess of the known matter content, and remarkably smooth and unclustered across the universe. While the most commonly accepted answer is that a cosmological constant is responsible, alternatives abound. This thesis is primarily concerned with such alternatives; both their theoretical nature and observational consequences. In this thesis, we will dedicate Chapter 1 to a brief review on the fundamentals of general relativity, leading into the basics of theoretical cosmology. Following this we will recall some of the key observations that has lead to the standard CDM cosmology. The standard model has well known problems, many of which can be answered by the theoretical ideas of inflation. In Chapter 2 we explore these ideas, including a summary of classical field theory in the context of cosmology, upon which inflation is based. This also serves as the groundwork for Chapter 3, where the varied models of dark energy (and their motivations) are discussed - many of which are also reliant on field theory (such as quintessence). These notions are combined in a model described in Chapter 4, where we describe our own addition to a scenario that unifies dark energy and inflation. This addition - involving a coupling of the inflation field to an additional one - alter the way reheating takes place after inflation, removing some of the shortcomings of the original proposal. The analysis is extended in Chapter 5, to include the effect of quantum corrections. There we show that although a cursory analysis indicates a coupling between quintessence and some other field does not necessarily give rise to dangerously large quantum corrections, provided the effects of decoupling are taken into account. We move on in Chapter 6 to examine the basics of cosmological perturbation theory, and derive the general equations of motion for density and velocity perturbations for a system of fluids, allowing for the exchange of energy-momentum. We make use of this in Chapters 7 and 8, were we examine the growth of structure in a universe where energy is exchanged between dark matter and dark energy. In particular, in Chapter 7 we see that a particular form of the interaction can lead to an instability in the early universe, and we derive the condition for this to be the case. In Chapter 8, we discuss how a similar interaction can lead to a mimicry of modified gravity, and relate this directly to cosmological observations. Finally we summarise our conclusions and discuss avenues of future research in Chapter 9.

Mon travail de thèse porte sur l’analyse cosmologique de surveys d’amas de galaxies en rayons X. Les amas sont détectés par le satellite XMM grâce à leur émission X produite par effet Bremsstrahlung du gaz intra-amas. L’étude de la distribution des amas en fonction de leur masse et de leur distance permet de mesurer m, _8 et de contraindre l’équation d’état de l’énergie noire. Une nouvelle approche cosmologique, développée par Clerc et al (2012), se base uniquement sur la distribution de quantités observables en rayons X (flux et couleur). Mon travail a consisté à étendre cette approche en y adjoignant la mesure de la taille apparente de l’émission X des amas. C’est un paramètre qui dépend de la masse de l’amas et de sa distance et qui intervient directement dans la fonction de sélection du survey. J’ai tout d’abord évalué les performances de cette méthode avec une analyse de Fisher. J’ai également étudié l’effet de la dispersion de la relation masse-rayon sur le taux de détection des amas et donc sur les contraintes cosmologiques. Pour valider ces calculs j’ai, dans une seconde partie, utilisé des surveys d’amas X simulés : 100-10000 deg2 à partir d’un modèle purement analytique et 1000 deg2 avec un modèle semi-analytique sur des simulations numériques de matière noire (Aardvark). J’ai déterminé les erreurs sur les paramètres cosmologiques à partir des diagrammes de diagnostic X simuls en utilisant des logiciels de minimisation (MCMC, Amoeba). Ces calculs ont confirmé les prédictions de l’analyse de Fisher. En conclusion, les diagrammes X sont au moins aussi performants que la m´méthode traditionnelle basée sur N(M,z) et d’utilisation beaucoup plus rapide et simple. Je propose quelques applications pour le survey XXL. / Cosmology is one of the fundamental pillars of astrophysics, as such it contains many unsolvedpuzzles. To investigate some of those puzzles, we analyze X-ray surveys of galaxy clusters. These surveys are possible thanks to the bremsstrahlung emission of the intra-cluster medium. The simultaneous fit of cluster counts as a function of mass and distance provides an independent measure of cosmological parameters such as m, _8, and the dark energy equation of state w0. A novel approach to cosmological analysis using galaxy cluster data, called top-down, was developed in N. Clerc et al. (2012). This top-down approach is based purely on instrumental observables that are considered in a two-dimensional X-ray color-magnitude diagram. The method self-consistently includes selection effects and scaling relationships. It also provides a means of bypassing the computation of individual cluster masses. My work presents an extension of the top-down method by introducing the apparent size of the cluster, creating a three-dimensional X-ray cluster diagram. The size of a cluster is sensitive to both the cluster mass and its angular diameter, so it must also be included in the assessment of selection effects. The performance of this new method is investigated using a Fisher analysis. In parallel, I have studied the effects of the intrinsic scatter in the cluster size scaling relation on the sample selection as well as on the obtained cosmological parameters. To validate the method, I estimate uncertainties of cosmological parameters with MCMC method Amoeba minimization routine and using two simulated XMM surveys that have an increasing level of complexity. The first simulated survey is a set of toy catalogues of 100 and 10000 deg2, whereas the second is a 1000 deg2 catalogue that was generated using an Aardvark semi-analytical N-body simulation. This comparison corroborates the conclusions of the Fisher analysis. In conclusion, I find that a cluster diagram that accounts for the fluxes, colors, sizes, and redshifts of the clusters performs well. Additionally, I find that it is at least as efficient as the traditional M,z method for the same cluster samples. I also discuss a proposition to apply this method to the XXL survey data

Orientador: Horatiu Nastase / Resumo: Nesta tese, discutimos três modelos cosmológicos que são baseados direta ou indiretamente em ideias advindas de teoria das cordas. Depois de uma revisão geral de cosmologia em teoria das cordas, um resumo de cosmologia e teoria das cordas é apresentado, com ênfase nos conceitos fundamentais e teóricos. Então descrevemos como o acoplamento camaleônico pode potencialmente afetar as predições de inflação cósmica com campo único, com tratamento cuidadoso dos modos de perturbação cosmológica adiabáticos e de entropia. Além disso uma nova abordagem para a dualidade-T em soluções cosmológicas de supergravidade bosônica é discutida no contexto de teoria dupla de campos. Por fim, propomos uma nova prescrição para o mapa holográfico em cosmologia que pode ser usado para conectar modelos fundamentais de cosmologia holográfica com outras abordagens fenomenológicas. / Doutor

My overall claim in this paper is twofold: Firstly, the activity of developing arguments in favour of the existence of the Christian God is tenable and worthwhile and, secondly, the “infinite God objection” fails to undermine the kalam cosmological argument. Concerning the former, it is often claimed that the very activity of developing arguments in favour of God’s existence is futile. I argue, however, that such theistic arguments play an important role in the philosophy of religion, natural theology, and apologetics. Concerning the latter claim, I will attempt to show how the infinite God objection fails to undermine a notable theistic argument, namely, the kalam cosmological argument. As regards this objection, the proponents of the kalam cosmological argument face a dilemma – either an actual infinity cannot exist or God’s knowledge cannot be infinite. More specifically, this objection claims that God’s omniscience entails the existence of an actual infinity with God knowing an actual infinite number of future events and mathematical truths. My solution to this problem is that (1) God’s omniscience should be understood as maximal knowledge; (2) the existence of abstract objects (such as numbers and propositions) should be denied; and (3) God’s knowledge is non-propositional in nature. / MPhil, North-West University, Potchefstroom Campus, 2014

Thesis (Ph. D.)--University of Washington, 2005. / Vita. Includes bibliographical references (p. 103-111).

This dissertation proposes cosmological aesthetics as a critique of and contribution to geologic, geomorphic and geographical aesthetics. This argument is developed in the context of human geographers' growing interests in the dark, imperceptible and unknown forces and fields of Earth and the cosmos. Attention to such cosmic phenomena amplifies the porosity of distinctions between humans, nonhumans and matter; therefore we require an aesthetic theory at the limits of sensing. In developing this aesthetics, this dissertation draws conceptual support in particular from the non-anthropocentric philosophy of Alfred North Whitehead and from Isabelle Stengers' "ecologies of practice". At the same time, the elaboration of cosmological aesthetics emerges from a site-based creative ethnography of Studio Tomás Saraceno in Berlin, and more specifically, from a series of experiments in transdiciplinary collaboration, writing and teaching with Tomás Saraceno. This dissertation interrogates how the surfaces, webs, envelopes and interstices populating and propagating in Saraceno's artwork affect the transmission and distribution of sensation across spaces and scales: in short, how these forms become technologies of cosmo-aesthetic adventure. By engaging with Saraceno's art projects, from On Space Time Foam to hybrid webs and the Aerocene, and by participating in the atmospheric experiments of aerosolar sculptures, this dissertation articulates two core propositions of cosmological aesthetics: first, that aesthetic experience can create tangible, sensible relations with contexts that are far removed, or much wider than, the particular conditions in which we experiment. And second: such adventures in aesthetics emerge from practices bound together by the forces of obligation, attachment and crucially, imagination. Employing foremost the device of the web, cosmological aesthetics explores propositions for bodies to be creatively extended in a vast and vibrating cosmos.