We develop two new methods to measure the structure of matter around the Milky Way using stellar tidal streams from disrupting dwarf galaxies and globular clusters. The dark matter halo of the Milky Way is expected to be triaxial and filled with substructure, but measurements of the shape and profile of dark matter around the Galaxy are highly uncertain and often contradictory. We demonstrate that kinematic data from near-future surveys for stellar streams or shells produced by tidal disruption of stellar systems around the Milky Way will provide precise measures of the gravitational potential to test these predictions. We develop a probabilistic method for inferring the Galactic potential with tidal streams based on the idea that the stream stars were once close in phase space and test this method on synthetic datasets generated from N-body simulations of satellite disruption with observational uncertainties chosen to mimic current and near-future surveys of various stars. We find that with just four well-measured stream stars, we can infer properties of a triaxial potential with precisions of order 5--7 percent. We then demonstrate that, if the Milky Way's dark matter halo is triaxial and is not fully integrable (as is expected), an appreciable fraction of orbits will be chaotic. We examine the influence of chaos on the phase-space morphology of cold tidal streams and show that streams even in weakly chaotic regions look very different from those in regular regions. We discuss the implications of this fact given that we see several long, thin streams in the Galactic halo; our results suggest that long, cold streams around our Galaxy must exist only on regular (or very nearly regular) orbits and potentially provide a map of the regular regions of the Milky Way potential. We then apply this understanding of stream formation along chaotic orbits to the interpretation of a newly-discovered, puzzling stellar stream near the Galactic bulge. We conclude that the morphology of this stream is consistent with forming along chaotic orbits due to the presence of the time-dependent Galactic bar. These results are encouraging for the eventual goal of using flexible, time-dependent potential models combined with larger data sets to unravel the detailed shape of the dark matter distribution around the Milky Way.

Over much of the last century evidence has been building for a new component of our universe that interacts primarily through gravitation. Known as cold dark matter, this non-luminous source is predicted to constitute 83% of matter and 26% of mass-energy in the universe. Experiments are currently searching for dark matter via its possible creation in particle colliders, annihilation in high-density regions of the universe, and interactions with Standard Model particles. So far dark matter has eluded detection so its composition and properties remain a mystery. Weakly interacting massive particles (WIMPs) are hypothetical elementary particles that interact on the scale of the weak nuclear force. They naturally satisfy predictions from extensions of the Standard Model, and are one of the most favored dark matter candidates. A number of direct detection experiments dedicated to measuring their predicted interactions with atomic nuclei have been constructed over the last 25 years. Liquid xenon dual phase time projection chambers (TPCs) have led the field for spin-independent WIMP searches at WIMP masses of >10 GeV/c^2 for most of the last decade. XENON1T is the first tonne-scale TPC, and with 278.8 days of dark matter data has set the strictest limits on WIMP-nucleon interaction cross sections above WIMP masses of 6 GeV/c^2, with a minimum of 4.1 x10^{-47} cm^2 at 30 GeV/c^2. XENON1T and the analysis that led to this result are discussed, with an emphasis on electronic and nuclear recoil calibration fits, which help discriminate between background and WIMP-like events. Interactions in liquid xenon produce light and charge that are measured in TPCs. These signals are attenuated by electronegative impurities including O_2 and H_2O, which are homogeneously distributed throughout the liquid xenon. The decrease in observables enlarges the uncertainty in our analysis, and can decrease our sensitivity. Methods on measuring the charge loss are presented, and a physics model that describes the behavior of the electronegative impurity concentration over the lifetime of XENON1T is derived. The model is shown to successfully explain the more than two years of data.

It is now a consolidated fact that our Universe is undergoing an accelerated expansion. According to Einstein's General Relativity, if the main constituents of our Universe were ordinary and cold dark matter, then we would expect it to be contracting and collapsing due to matter's attractive nature. The simplest explanation we have for this acceleration is in the form of a component with a negative ratio of pressure to density equal to -1 known as cosmological constant, Λ , presently dominating over baryonic and cold dark matter. However, the Λ Cold Dark Matter (Λ CDM) model suffers from a well known fine tuning problem. This led to the formulation of dark energy and modified gravity theories as alternatives to the problem of cosmic acceleration. These theories either include additional degrees of freedom, higher-order equations of motion, extra dimensionalities or imply non-locality. In this thesis we focus on single field scalar tensor theories embedded within Horndeski gravity. Even though there is currently doubt on their ability to explain cosmic acceleration without having a bare cosmological constant on their action, the degree of freedom they introduce mediates an additional fifth force. And while this force has to suppressed on Solar system scales, it can have interesting and observable effects on cosmological scales. Over the next decade there is a surge of surveys that will improve the understanding of our Universe on the largest scales. Hence, in this work, we take several different modified gravity theories and study their impact on cosmological observables. We will analyze the dynamics of linear perturbations on these theories and clearly highlight how they deviate from Λ CDM, allowing to break the degeneracy at the background level. We will also study the evolution of the gravitational potentials on sub horizon scales and provide simplified expressions at this regime and, for some models, obtain constraints using the latest data.

Nesta tese, estudamos cosmologias com criação de matéria como alternativa ao modelo $\\Lambda$CDM. Generalizamos a equação de Boltzmann relativística com um termo de produção de partículas fenomenológico, de tal forma que a equação resultante seja capaz de reobter os resultados da termodinâmica de não-equilíbrio das equações de balanço e evolução de temperatura. Após obter o termo correto para a equação generalizada de Boltzmann, investigamos como o formalismo proposto altera a equação de evolução de relíquias cósmicas na presença de criação gravitacional de partículas. / In this thesis, we study matter creation cosmologies as an alternative to the $\\Lambda$CDM model. We generalize the relativistic Boltzmann equation with a phenomenological particle production term, in such a way that the resulting equation will be able to reproduce the non-equilibrium thermodynamics results of the balance equations and temperature evolution law. After obtaining the correct term to the generalized Boltzmann equation, we investigate how the proposed formalism changes the cosmic relic evolution equation in the presence of gravitational particle creation.

No description available.

<p>Recent measurements show that dark matter makes up at least one fifth of the total energy density of the Universe. The nature of the dark matter is one of the biggest mysteries in current particle physics and cosmology.</p><p>Big Bang nucleosynthesis limits the amount of baryonic matter that can exist, and shows that the dark matter has to be non-baryonic. Particle physics provides some candidates for non-baryonic matter that could solve the dark-matter problem, weakly interacting massive</p><p>particles (WIMPs) being the most popular. If these particles were created in the early Universe a substatial relic abundance would exist today. WIMPs in our galactic halo could be gravitationally bound in the Solar System and accumulate inside heavy bodies like the Earth. Supersymmetric extensions to the Standard Model give a viable WIMP dark matter candidate in the form of the lightest neutralino. This thesis describes an indirect search for WIMPs by the neutrino signature from neutralino annihilation at the core of the Earth using the AMANDA detector. As opposed to previous dark matter searches with AMANDA, this work focuses on the hypothesis of a relatively light WIMP particle with mass of 50-250GeV/c²</p><p>The AMANDA neutrino telescope is an array of photomultiplier tubes installed in the clear glacier ice at the South Pole which is used as Cherenkov medium. Data taken with AMANDA during the period 2001-2003 is analyzed. The energy threshold of the detector is lowered by the use of a local correlation trigger, and the analysis is taylored to select vertically upgoing low energy events. No excess above the expected atmospheric neutrino background is found. New limits on the flux of muons from WIMP annihilations in the center of the Earth are calculated.</p>

Dark matter particles in the form of supersymmetric Weakly Interacting Massive Particles (WIMPs) could accumulate in the centre of the Sun because of gravitational trapping. Pair-wise annihilations of WIMPs could create standard model particles out of which neutrinos could reach the Earth. Data from the IceCube 22-string neutrino telescope have been searched for signals from dark matter annihilations in the Sun. Highly sophisticated analysis methods have been developed to discern signal neutrinos from the severe background of atmospheric particle showers. No signal has been found in a dataset of 104 days livetime taken in 2007, and an upper limit has been placed on the muon flux in the South Pole ice induced by neutrinos from the Sun, reaching down to 330 km-2y-1. The flux limit has been converted into an upper limit on the neutralino scattering cross-section, which reaches down to 2.8*10-40 cm2 for spin-dependent interactions. / Four articles are appended to the thesis:I. G. Wikström for the IceCube collaboration, Proc. of the 30th ICRC,arXiv/0711.0353 [astro-ph] (2007) 135.II. A. Gross, C. Ha, C. Rott, M. Tluczykont, E. Resconi, T. DeYoung and G. Wikström for the IceCube Collaboration, Proc. of the 30th ICRC,arXiv/0711.0353 [astro-ph] (2007) 11.III. G. Wikström and J. Edsjö, JCAP 04 (2009) 009.IV. R. Abbasi et al. (IceCube collaboration), accepted for publication in Phys. Rev. Lett., arXiv/0902.2460v3 [astro-ph.CO] (2009). / IceCube

<p>We explore a model of dark matter called wave dark matter (also known as scalar field dark matter and boson stars) which has recently been motivated by a new geometric perspective by Bray. Wave dark matter describes dark matter as a scalar field which satisfies the Einstein-Klein-Gordon equations. These equations rely on a fundamental constant Upsilon (also known as the ``mass term'' of the Klein-Gordon equation). Specifically, in this dissertation, we study spherically symmetric wave dark matter and compare these results with observations of dwarf spheroidal galaxies as a first attempt to compare the implications of the theory of wave dark matter with actual observations of dark matter. This includes finding a first estimate of the fundamental constant Upsilon.</p><p>In the introductory Chapter 1, we present some preliminary background material to define and motivate the study of wave dark matter and describe some of the properties of dwarf spheroidal galaxies.</p><p>In Chapter 2, we present several different ways of describing a spherically symmetric spacetime and the resulting metrics. We then focus our discussion on an especially useful form of the metric of a spherically symmetric spacetime in polar-areal coordinates and its properties. In particular, we show how the metric component functions chosen are extremely compatible with notions in Newtonian mechanics. We also show the monotonicity of the Hawking mass in these coordinates. Finally, we discuss how these coordinates and the metric can be used to solve the spherically symmetric Einstein-Klein-Gordon equations.</p><p>In Chapter 3, we explore spherically symmetric solutions to the Einstein-Klein-Gordon equations, the defining equations of wave dark matter, where the scalar field is of the form f(t,r) = exp(i omega t) F(r) for some constant omega in R and complex-valued function F(r). We show that the corresponding metric is static if and only if F(r) = h(r)exp(i a) for some constant a in R and real-valued function h(r). We describe the behavior of the resulting solutions, which are called spherically symmetric static states of wave dark matter. We also describe how, in the low field limit, the parameters defining these static states are related and show that these relationships imply important properties of the static states.</p><p>In Chapter 4, we compare the wave dark matter model to observations to obtain a working value of Upsilon. Specifically, we compare the mass profiles of spherically symmetric static states of wave dark matter to the Burkert mass profiles that have been shown by Salucci et al. to predict well the velocity dispersion profiles of the eight classical dwarf spheroidal galaxies. We show that a reasonable working value for the fundamental constant in the wave dark matter model is Upsilon = 50 yr^(-1). We also show that under precise assumptions the value of Upsilon can be bounded above by 1000 yr^(-1).</p><p>In order to study non-static solutions of the spherically symmetric Einstein-Klein-Gordon equations, we need to be able to evolve these equations through time numerically. Chapter 5 is concerned with presenting the numerical scheme we will use to solve the spherically symmetric Einstein-Klein-Gordon equations in our future work. We will discuss how to appropriately implement the boundary conditions into the scheme as well as some artificial dissipation. We will also discuss the accuracy and stability of the scheme. Finally, we will present some examples that show the scheme in action.</p><p>In Chapter 6, we summarize our results. Finally, Appendix A contains a derivation of the Einstein-Klein-Gordon equations from its corresponding action.</p> / Dissertation

One of the greatest mysteries of the universe that, for the present, puzzles the mind of most astronomers, cosmologists and physicists is the question: "What makes up our universe?". This is due to how a certain substance named Dark Matter came under speculation. It is believed this enigmatic substance, of type unknown, accounts for almost three-quarters of the cosmos within the universe, could be the answer to several questions raised by the models of the expanding universe astronomers have created, and even decide the fate of the expansion of the universe. There is strong observational evidence for the dominance of non-baryonic Dark Matter (DM) over baryonic matter in the universe. Such evidence comes from many independent observations over different length scales. The most stringent constraint on the abundance of DM comes from the analysis of the Cosmic Microwave Background (CMB) anisotropies. In particular, the WMAP (Wilkinson Microwave Anisotropy Probe) experiment restricts the abundance of matter and the abundance of baryonic matter in good agreement with predictions from Big Bang Nucleosynthesis. It is commonly believed that such a non-baryonic component could consist of new, as yet undiscovered, particles, usually referred to as WIMPs (Weakly Interacting Massive Particles). Some extensions of the standard model (SM) of particle physics predict the existence of particles that would be excellent DM candidates. In particular great attention has been dedicated to candidates arising in supersymmetric theories: the Lightest Supersymmetric Particle (LSP). In the most supersymmetric scenarios, the so-called neutralino seems to be a natural candidate, being stable in theories with conservation of R-parity and having masses and cross sections of typical WIMPs. The EDELWEISS collaboration is a direct dark matter search experiment, aiming to detect directly a WIMP interaction in a target material, high purity germanium crystal working at cryogenic temperatures. It relies in the measurement of nuclear recoils that produce measurable effects in the crystal such ionization and heat. My PhD thesis is organized as follows. The first chapter aims to provide an introduction to the theoretical framework and the scientific motivation for the following work. The nature of DM has been one of the most challenging topics in contemporary physics since the first evidences of its existence had been found in the 1930s. Cosmologists and astrophysicists on one side, together with particle theorists on the other have put a lot of effort into this field: I will briefly account for their achievements and for the experimental strategies which can be set in this scenario. Since this thesis work was carried out within the EDELWEISS-II direct dark matter experiment, I will focus the next chapter on this topic, describing the main features. The second chapter is related to the set-up of the EDELWEISS-II, the current stage of the EDELWEISS experiment necessary after a first phase that achieved the best upper limit on the WIMP elastic scattering on nucleon as a function of WIMP mass in 2004. [....]

La teoría científica de más éxito hoy en día, sobre el origen y la evolución del universo, es conocida como el modelo estándar del Big Bang, el cual es una de las construcciones intelectuales más ambiciosas de la humanidad. Se basa en dos ramas bien consolidadas de la física teórica, a saber, la teoría de la Relatividad General y el Modelo Estándar de la física de partículas, y es capaz de hacer predicciones sólidas, como la expansión del universo, la existencia del fondo de radiación de microondas y las abundancias relativas de los elementos ligeros. Algunas de las predicciones teóricas ya han sido confirmadas por observaciones muy precisas.Según la cosmología estándar del Big Bang, el universo primitivo consistía en un plasma muy caliente y denso que se expandió y se enfrió continuamente hasta el presente, dando paso a una serie de transiciones de fase cosmológicas, donde las teorías que describen el universo en cada fase son distintas. Dado que las energías del universo primitivo fueron mucho más altas que las alcanzadas en experimentos terrestres, el estudio del universo primitivo podría ofrecernos importantes informaciones sobre nuevas interacciones y nuevas partículas, abriendo nuevas direcciones para la extensión del Modelo Estándar de la física de partículas.Como ya he mencionado anteriormente, durante la expansión del universo ocurrieron varias transiciones de fase que dejaron su huella sobre el estado presente del universo. Las observaciones sugieren que durante una de estas transiciones de fase, el universo primitivo sufrió un periodo de expansión acelerada, conocido como inflación. Aunque no forma parte de la cosmología estándar, la inflación es capaz de solucionar de una manera simple y elegante casi todos los problemas relacionados con el modelo estándar del Big Bang, y debería tenerse en cuenta en cualquier extensión posible de la teoría. Las observaciones también revelan la existencia de dos formas de energía desconocidas, a saber, materia oscura y energía oscura. La materia oscura es una forma de materia no relativista y no bariónica, que solamente puede ser detectada indirectamente, mediante su interacción con la materia normal. La energía oscura es un tipo de sustancia con presión negativa, que empezó a dominar recientemente y que es la causa de la aceleración de la expansión del universo.En esta tesis doctoral presento varios modelos originales propuestos para resolver algunos de los problemas de la cosmología estándar, como posibles extensiones del modelo del Big Bang. Algunos de estos modelos introducen nuevas simetrías y partículas con el fin de explicar la inflación y la energía oscura y/o la materia oscura en una descripción unificada. Uno de los modelos es propuesto para explicar la energía oscura del universo, a través de un nuevo campo escalar que oscila en un potencial. / The most successful scientific theory today about the origin and evolution of the universe is known as the standard Big Bang model, which is one of the most ambitious intellectual constructions of the humanity. It is based on two consolidated branches of theoretical physics, namely, the theory of General Relativity and the Standard Model of particle physics, and is able to make robust predictions, such as the expansion of the universe, the existence of the cosmic microwave background radiation and the relative primordial abundance of light elements. Some of the theoretical predictions have already been confirmed by very precise observations.According to the standard Big Bang cosmology, the early universe consisted of a very hot and dense plasma that continuously expanded and cooled up to the present, giving place to a series of cosmological phase transitions, where the theories describing the universe in each phase are different. Given that the energies of the early universe were much higher than those reached in terrestrial experiments, the study of the early universe might give us important information about new interactions and new particles, opening new directions for extending the Standard Model of particle physics.As already mentioned above, during the expansion of the universe, different phase transitions occurred, which left their imprint on the present state of the universe. Observations suggest that during a very early phase transition the universe suffered a stage of accelerated expansion, known as inflation. Although inflation is not included in the standard cosmology, it is able to solve in a simple and elegant manner almost all of the shortcomings related to the standard Big Bang model, and should be taken into account in any possible extension of the theory. Observations also reveal evidence of the existence of two unknown forms of energy, i.e., dark matter and dark energy. Dark matter is a form of non-relativistic and non-baryonic matter, which can only be detected indirectly, by its gravitational interactions with normal matter. Dark energy is a kind of substance with negative pressure, which started to dominate recently and causes the accelerated expansion of the universe. In this PhD Thesis, I present a few original models proposed to solve some of the shortcomings of the standard cosmology, as possible extensions of the Big Bang model. Some of these models introduce new symmetries and particles in order to explain inflation and dark energy and/or dark matter in a unified description. One of the models is proposed for explaining the dark energy of the universe, by means of a new scalar field oscillating in a potential.The most successful scientific theory today about the origin and evolution of the universe is known as the standard Big Bang model, which is one of the most ambitious intellectual constructions of the humanity. It is based on two consolidated branches of theoretical physics, namely, the theory of General Relativity and the Standard Model of particle physics, and is able to make robust predictions, such as the expansion of the universe, the existence of the cosmic microwave background radiation and the relative primordial abundance of light elements. Some of the theoretical predictions have already been confirmed by very precise observations.According to the standard Big Bang cosmology, the early universe consisted of a very hot and dense plasma that continuously expanded and cooled up to the present, giving place to a series of cosmological phase transitions, where the theories describing the universe in each phase are different. Given that the energies of the early universe were much higher than those reached in terrestrial experiments, the study of the early universe might give us important information about new interactions and new particles, opening new directions for extending the Standard Model of particle physics.As already mentioned above, during the expansion of the universe, different phase transitions occurred, which left their imprint on the present state of the universe. Observations suggest that during a very early phase transition the universe suffered a stage of accelerated expansion, known as inflation. Although inflation is not included in the standard cosmology, it is able to solve in a simple and elegant manner almost all of the shortcomings related to the standard Big Bang model, and should be taken into account in any possible extension of the theory. Observations also reveal evidence of the existence of two unknown forms of energy, i.e., dark matter and dark energy. Dark matter is a form of non-relativistic and non-baryonic matter, which can only be detected indirectly, by its gravitational interactions with normal matter. Dark energy is a kind of substance with negative pressure, which started to dominate recently and causes the accelerated expansion of the universe. In this PhD Thesis, I present a few original models proposed to solve some of the shortcomings of the standard cosmology, as possible extensions of the Big Bang model. Some of these models introduce new symmetries and particles in order to explain inflation and dark energy and/or dark matter in a unified description. One of the models is proposed for explaining the dark energy of the universe, by means of a new scalar field oscillating in a potential.