Observations from a broad range of astrophysical scales have forced us to the realization that the well understood matter comprising the stars and galaxies we see around us accounts for only a small fraction of the total mass of the Universe. An amount roughly five times larger exist in the form of dark matter about which we have virtually no direct evidence apart from its large scale gravitational effects. It is also known that the largest contribution to the energy density of the universe is the dark energy, a negative pressure form of energy which will not be dealt with here. I will present a candidate for the dark matter which is based completely in known physics and which presents several possible observational signatures. In this model the dark matter is composed of dense nuggets of baryonic matter and antimatter in a colour superconducting state. If these object are sufficiently massive their low number density will make them effectively dark in the sense that collisions with visible matter become infrequent. This work presents the basics of dark matter as a colour superconductor and then uses the physical properties of the quark nuggets to extract observational consequences. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Dark adaptation thresholds have been determined for a group of ocular hypertensives and a group of equivantly aged normal controls under two separate conditions of colored pre-adaptation and test. The method relies on the Purkinje shift to obtain two dark adaptation curves for each subject that cross when the initially favored long wavelength (yellow) curve is superceded by the shorter one (blue-green): under photopic conditions, the yellow and blue-green stimuli are equally efficient in stimulating the retina, as they are equated for brightness during pre-adaptation; as dark adaptation proceeds the blue-green and yellow thresholds display an early relation wherein yellow light has the lower thresholds; then the curves cross and blue-green light displays lower thresholds. Each curve is obtained separately with a pre-adaptation of 80 ft. lamberts for 5 minutes and a centrally fixated 11° test patch that matches the spectral composition of the pre-adaptation. A variety of variables are derived from threshold intensity measurements and they are analyzed for age effects, disease effects, and their interactions. Age and disease both depress blue-green and yellow cone sensitivity, delay cross-over time, and increase the total change in sensitivity over 13 minutes of dark adaptation. Interactions magnify differences. Color discrimination is found to be associated with dark adaptation thresholds, sometimes specifically as to the type of color defect and the colored dark adaptation curve showing losses. Intraocular pressure, macular sensitivity, and diastolic blood pressure are also significantly correlated with dark adaptation thresholds. Disease and age effects are elaborated in terms of changes in the ocular media, macular pigmentation changes, as well as deterioration of rod and cone processes. In addition, aging is seen to be complicated by peculiarities in the selection of the normal population. The associations demonstrated for clinical and color vision variables with dark adaptation thresholds suggest (1) that open angle glaucoma may be caused by deficient nutrition to the optic nerve head or to the retina itself, (2) that central rod and cone vision undergo changes very early in the course of the disease. A preliminary study using the two-filter method with well-established glaucoma confirms that similar, more pronounced losses in dark adaptation take place later in the disease's development. / Arts, Faculty of / Psychology, Department of / Graduate

Hidden sector or dark sector states appear in many extensions to the Standard Model (SM), to provide particle mediators for dark matter in the universe or to explain astrophysical observations such as the positron excess in the cosmic microwave background radiation flux. A hidden or dark sector can be introduced with an additional U(1)d dark gauge symmetry. The discovery of the Higgs boson in 2012 during Run 1 by the Large Hadron Collider (ATLAS and CMS) opens a new and rich experimental program for Beyond Standard Model physics (BSM) based on the Higgs Portal. This exotic discovery route uses couplings to the dark sector at the Higgs level, which were not experimentally accessible before. This thesis presents the searches of possible exotic decays: H → ZdZ(d) → 4` where Zd is a dark vector boson. It had been initiated in the Run 1 period of the LHC using the ATLAS detector at CERN. The results showed (tantalizingly) two signal events where none were expected, so that in the strict criteria of High Energy Physics, the result was not yet statistically significant. The Run 1 analysis for a 8 TeV collision energy is further developed in Run 2 with a 13 TeV collision energy, to expand the search area, take advantage of higher statistics, a higher Higgs production cross section, and substantially better performance of the ATLAS detector. In this work, the search is further broadened and includes allowing the mass of the originating boson (the dark Higgs S) to vary from the SM value. This allows the search for the dark vector boson to also explore higher or lighter masses than the SM Higgs boson. This extended search is efficient and could include a more general class of models, with the mass constraint of the SM Higgs portal lifted. This thesis reviews the analysis results from Run 1 and Run 2, and presents its iteration in the full Run 2 search by focusing on its new channel where the additional scalar S (with mS 6= mH) decays to 4` via two dark vector boson states Zd . The case where the Higgs decays to 4` via two Zd (H → ZdZd → 4`) and also called high mass channel, has been just unblinded. Nineteen data events are observed where 14 were predicted. In overall, the data are consistent with the Monte Carlo prediction. No evidence of deviation from the Standard Model expectations are observed. / College of Engineering, Science and Technology / Ph. D. (Physics)

Thesis (Ph.D.)--Boston University / The existence of Dark Matter was first proposed by Fritz Zwicky in 1933, based on the observed velocity distribution of galaxies in the Coma Cluster. Subsequent studies of visible mass and velocity distributions in other galaxies have confirmed Zwicky's original observation; there is now little doubt that Dark Matter exists. However, due to the fact that Dark Matter interacts very weakly through non-gravitational forces, nothing is known about the nature of Dark Matter. It is believed that Dark Matter particles are streaming toward the Earth, in the Earth's rest frame, from the direction of the constellation Cygnus. Observation of this so-called Dark Matter 'wind' with a direction-sensitive dark matter particle detector would be compelling evidence that Dark Matter does consist of a gas of discrete particles as a new form of matter. The DMTPC collaboration is developing such a detector, and this thesis describes R&D work in support of that project. The DMTPC technique for looking for Dark Matter relies on Dark Matter particles interacting with atomic nuclei, causing the nuclei to recoil and to leave optical signals that can be detected. Since neutrons are electrically neutral and collide with nuclei, they can mimic Dark Matter signals. Therefore, the reduction of neutron background is critical to the successful detection and identification of Dark Matter particles. One important aspect of this thesis is to fully understand and quantify neutron interactions with our detector. In addition to providing information for understanding Dark Matter experiments, this work also allows us to understand how our device can be used as a neutron detector. We have been able to measure a number of neutron events in a variety of experimental runs both with and without neutron sources such as a neutron generator and 252 Cf. From these runs, we have obtained data for both elastic and inelastic interactions of neutrons of various energy ranges with detector gas nuclei. In this thesis, I will also discuss our current background data taking for the Dark Matter research and our plan for scaling up the detector to 100 m 3 for a competitive Dark Matter search.

La nature de l’énergie noire et de la matière noire est encore un mystère. De futures missions spatiales nous permettrons d’observer les propriétés et la distribution de milliards de galaxies mais quelle est la meilleure manière de contraindre la physique de ces composantes inconnues avec une telle quantité de données ? Le but de cette thèse est de chercher de nouvelles sondes du secteur sombre de l’univers dans le régime linéaire et non-linéaire de la formation des structures. La physique du secteur sombre laisse des empreintes dans la distribution des grandes structures à un temps donné (espace réel). Cependant leur distribution apparente telle que vue par un observateur (espace des redshifts) est légèrement différente de celle dans l’espace réel. En effet, les messagers (comme la lumière) sont perturbés pendant leur trajet depuis une source vers un observateur. Dans ce cas, quelle est la relation entre espace réel et espace des redshifts ? Comment extraire des informations cosmologiques de cette transformation ? L’essentiel de mon travail était de simuler des observables tout en prenant en compte tous les effets relativistes au premier ordre dans l’approximation de champs faible. Le lentillage gravitationnel faible modifie la position apparente des sources ainsi que leurs propriétés (forme, luminosité) tandis que les perturbations en redshift changent la distance radiale apparente des objets. Pour aborder ces questions, nous avons réalisé une simulation N-corps de grande taille et très résolue, idéale pour étudier les halos de taille entre la Voie Lactée et les amas de galaxie. Ensuite, nous avons suivi le trajet de photons dans la simulation en intégrant directement les équations de géodésique en utilisant comme seule approximation l’approximation de champs faible. Nous avons développé un algorithme qui nous permet de connecter un observateur à des sources via des géodésiques nulles. Par la suite, la matrice de lentillage est calculée grâce à un faisceaux lumineux tandis que le décalage spectral vers le rouge est directement calculé via sa définition donnée par la relativité générale. Grâce à cette bibliothèque de suivi de rayons lumineux, nous avons pu construire des catalogues de halos qui prennent en compte les effets relativistes. Grâce à ces catalogues nous avons pu retrouver des résultats standard à propos des distorsions dans l’espace des redshifts, du lentillage, et de l’effet Sachs Wolfe intégré avec grande précision. Nous avons également étudié le couplage subtil entre les distorsions dans l’espace des redshifts et le lentillage : Le lentillage Doppler. Enfin, nous avons exploré en détail les distorsions dans l’espace des redshifts dû aux effets relativistes. Avec notre simulation nous avons pu, pour la première fois, calculer le dipole de la function de corrélationcroisée entre 5 et 150 h − 1 Mpc, en incluant tous les termes relativistes. Aux grandes échelles nous retrouvons les résultats de la théorie linéaire : le dipole est dominé par l’effet Doppler dû à la présence d’un observateur à distance finie. Cependant, aux échelles non linéaires le dipole est dominé par l’effet de décalage spectral vers le rouge gravitationnel. Le dipole peut être une sonde du potentiel et dans ce cas du secteur sombre. Ce travail trouve beaucoup d’applications : la fonction de corrélation croisée entre différents observables (liées aux effets relativistes) pour différentes sources à des positions différentes peut être une nouvelle sonde intéressante pour le secteur sombre. / The nature of dark energy and dark matter is still a mystery. Future surveys will observe the property and distribution of billions of galaxies but what is the best way to constrain the physics of these unknown components from this data deluge? The goal of this thesis is to search for new probes of the dark sector of the universe within the linear and non-linear regime of structure formation. The physics of the dark sector leaves specific imprints in the distribution of Large-Scale Structures (LSS) at a given time (i.e. in real space). However their apparent distribution as seen by a given observer (i.e. in redshift space) slightly differs from the real one. This is because messengers (light) are perturbed in their path from the sources to the observer. What is the relation between real space and redshift space? How to extract cosmological information from these subtle Redshift-Space Distortions (RSD)? The main part of my work was to produce simulated observables taking into account all relativistic effects at first order in the weak field approximation. Weak Lensing (WL) modifies the apparent angular position of an object, as well as its properties (shape, luminosity). Redshift perturbations change the apparent radial distance of an object. To address these questions, we perform a large and highly resolved N-body simulation ideal to investigate halos from Milky-Way size to galaxy cluster size. We then perform backward ray-tracing directly integrating the geodesic equations using as its only assumption the weak field approximation. We develop a geodesic-finder to guaranty that light-rays connect all the sources to the observer. The lensing distortion matrix is then computed by launching a beam of light-rays while the redshift is directly computed from its definition in general relativity. Thanks to this unique ray-tracing library we construct halo catalogs including relativistic effects. Based on these catalogs we are able to recover standard results about RSD, WL and Integrated Sachs Wolfe (ISW) effect with high accuracy. We also investigate the subtle coupling between RSD and lensing: Doppler lensing. Finally we explore in detail relativistic RSD. Thanks to the large statistics of our simulations we are able for the first time to compute the dipole of the halo cross-correlation from 5 to 150 h − 1 Mpc including all relativistic terms. At large-scale we recover the results from linear calculation: the dipole is dominated by Doppler effect in the presence of a finite distant observer. However at smaller non-linear scales the dipole is dominated by the gravitational redshift perturbation. The dipole can therefore be a new probe of the potential and therefore of the dark sector. This work opens a wide range of applications: the cross-correlation between each observable (related to relativistic effects) for different sources at different location can possibly be new powerful probe of the dark sector.

No description available.

Modern cosmology has reached an important juncture, at which the ability to make measurements of unprecedented accuracy has led to conclusions that are a fundamental challenge to natural science. The discovery that, in our current best model, the dynamics of the Universe are completely dominated by unseen dark matter and dark energy can do little but completely alter the shape of physics research in the 21st Century. Unfortunately,much of our insight into these phenomenamust come from observations of visible matter alone; this raises serious problems, as the tracing of dark matter by visible matter is as yet poorly understood. Gravitational lensing offers strong prospects for probing the interwoven history of dark and visible matter, as mass in any form may be detected where it exists untraced by baryons. In this Thesis I describe advances made in the field of weak gravitational lensing, which constrains the properties of the matter distribution on cosmological scales using a statistical analysis of the coherent gravitational distortions of distant galaxy images. I summarize the development of gravitational flexion, a higher order extension to traditional weak lensing, and describe my work done to bring the study of flexion to a stage where it may be employed to make accurate cosmological measurements. I show how flexion is sensitive to matter structure on smaller physical scales than existing lensing techniques and, therefore, promises to shed new light upon key untested predictions of cosmological models if it can be measured to sufficient accuracy. I discuss the success of my efforts in this direction, and describe the issues to be encountered in the careful analysis of this subtle gravitational signal. This research has involved advances in many areas: the calculation of theoretical flexion predictions, the refinement of image analysis methods for accurate galaxy shape estimation, and the practical application of these new flexion techniques to extragalactic imaging data. The culmination of these efforts is a new maximum likelihood analysis of the galaxy-galaxy lensing signal in the Hubble Space Telescope Galaxy Evolution from Morphology and SEDs (GEMS) Survey, incorporating improvements and modifications necessary for the combination of flexion with traditional weak lensing measurements. The results of this work, and particularly the extent to which measurements of flexion provide extra cosmological insight, are discussed in detail. The conclusion is a summary of all that has been learned about the use of flexion as an accurate probe of cosmology, and a discussion of its prospects for answering some of the many questions that remain about dark matter. Within the next few year wide-area survey telescopes will begin imaging huge volumes of deep space, with the measurement of the gravitational lensing signal being given high priority in the analysis of these data. Within this context, the primary inquiry of this Thesis is the extent to which the application of flexion measurement techniques will help shed new light upon the unseen, and currently poorly understood, components of the Universe.

Neste trabalho, estudamos modelos cosmológicos em que a energia escura foi tratada como um campo de matéria que interage com a matéria escura. Três modelos distintos foram considerados. O primeiro trata tanto a matéria escura fria quanto a energia escura como fluidos perfeitos. O termo de interação entre eles é dado por uma expressão com origem fenomenológica que postulamos existir na equação de balanço entre esses dois fluidos. Dadas as equações no universo plano de Friedmann-Robertson-Walker (FRW), pudemos escrever uma versão covariante para as equações de balanço. Com isso, as equações de balanço em um universo de FRW perturbado linearmente foram obtidas. Isso, por sua vez, permitiu que a estabilidade das equações diferenciais obtidas fosse estudada. O segundo modelo tem origem em modelos de f(R). Esses modelos propõem uma generalização da Relatividade Geral ao considerar a ação da gravidade como um funcional do escalar de Ricci, R. Através de uma transformação conforme, foi possível reinterpretar os modelos de f(R) como modelos em que um campo escalar canônico, que representa a energia escura, interage com os campos da matéria. Através do princípio da ação, obtivemos as equações de movimento e o tensor de energia-momento para nosso sistema. Com o campo escalar sendo interpretado como um fluido perfeito, pudemos, por fim, obter equações de balanço entre fluidos perfeitos tanto no nível de fundo quanto no universo perturbado linearmente. O terceiro modelo começa com a lagrangiana, em um espaço-tempo de FRW, de um campo escalar canônico, que representa a energia escura, e um campo fermiônico de spin-1/2, que representa a matéria escura. Um termo de interação de Yukawa entre esses campos foi postulado existir na lagrangiana. Novamente através do princípio da ação, obtivemos as equações de movimento e o tensor de energia-momento para esses campos. Essas equações de movimento puderam, por fim, ser reescritas como equações de balanço entre fluidos perfeitos tanto no nível de fundo quanto no universo perturbado linearmente. / In this work we studied cosmological models in which the dark energy was treated as a field of matter that interacts with dark matter. Three different models were considered. The first one treats both the cold dark matter and the dark energy as perfect fluids. The interaction term between them is given by a expression with phenomenological origin that we postulated to exist in the balance equations between these two fluids. Given the equations in the flat Friedmann-Robertson-Walker (FRW) universe, we wrote a covariant version of the balance equations. Thus, the balance equations in a linearly perturbed FRW universe were obtained. This, in turn, allowed the stability of the obtained differential equations to be studied. The second model comes from f(R) models. These models propose a generalization of General Relativity by considering the action for gravity as a functional of the Ricci scalar, R. Through a conformal transformation, it was possible to reinterpret the f(R) models as models in which a canonical scalar field, which represents the dark energy, interacts with matter fields. Through the principle of least action, we obtained the equations of motion and the energy-momentum tensor for our system. With the scalar field being interpreted as a perfect fluid, we obtained equations of balance for perfect fluids at both the background level and in the linearly perturbed universe. The third model starts with the Lagrangian, in a FRW space-time, of a canonical scalar field, which represents the dark energy, and of a fermionic field of spin-1/2, which represents the dark matter. A Yukawa interaction term between these fields was postulated to exist in the Lagrangian. Again, through the principle of least action, we obtained the equations of motion and the energy-momentum tensor for these fields. These equations of motion could then be rewritten as balance equations for perfect fluids at both the background level and in the linearly perturbed universe.

In this thesis we go beyond the standard cosmological LCDM model and study the effect of an interaction between dark matter and dark energy. Although the LCDM model provides good agreement with observations, it faces severe challenges from a theoretical point of view. In order to solve such problems, we first consider an alternative model where both dark matter and dark energy are described by fluids with a phenomenological interaction given by a combination of their energy densities. In addition to this model, we propose a more realistic one based on a Lagrangian density with a Yukawa-type interaction. To constrain the cosmological parameters we use recent cosmological data, the CMB measurements made by the Planck satellite, as well as BAO, SNIa, H0 and Lookback time measurements. / Nesta tese vamos além do modelo cosmológico padrão, o LCDM, e estudamos o efeito de uma interação entre a matéria e a energia escuras. Embora o modelo LCDM esteja de acordo com as observações, ele sofre sérios problemas teóricos. Com o objetivo de resolver tais problemas, nós primeiro consideramos um modelo alternativo, onde ambas, a matéria e a energia escuras, são descritas por fluidos com uma interação fenomenológica dada como uma combinação das densidades de energia. Além desse modelo, propomos um modelo mais realista baseado em uma densidade Lagrangiana com uma interação tipo Yukawa. Para vincular os parâmetros cosmológicos usamos dados cosmológicos recentes como as medidas da CMB feitas pelo satélite Planck, bem como medidas de BAO, SNIa, H0 e Lookback time.

Neste trabalho discutimos um modelo baseado em teoria de campos para descrever a energia escura, no qual ela é representada por uma partícula ultra-leve situada em um mínimo metaestável de um potencial. Mostramos que a energia escura neste modelo decai em matéria escura durante o tempo de vida do universo, amenizando o problema da coincidência. / In the present work we discuss a field theory model in which dark energy is described by ultra-light particle situated at a metastable minimum of a potential. We show that dark energy in this model decays into dark matter during a time scale corresponding to the age of the universe, alleviating the coincidence problem.