Tesis sobre el tema "Dark Matter, Dark Energy, Metrology"

In the last years, the standard model of cosmology has been corroborated by a wide number of astrophysical observations. Despite its undeniable success, nowadays there is little knowledge about the true nature of dark matter and dark energy. In this thesis we use a different approach to give an intriguing answer to these open problems, in the light of the corpuscular model of gravity. We give a general overview on the reasons behind the need for a corpuscular theory of the gravitational interaction. Then, we show that if the same picture is extended to cosmological spaces, dark energy naturally emerges as a quantum state of the gravitational dynamics, and it is described as a Bose-Einstein condensate of very soft and virtual gravitons without the necessity of introducing an exotic dark fluid. Besides, the cosmic condensate responds locally to the presence of baryonic matter, and the back-reaction manifests itself in the emergence of a dark force that mimics a dark matter behavior. In particular, at galactic scales the MOND formula for the acceleration is recovered. Then, a first attempt of estimating the back-reaction is proposed within the framework of Bootstrapped Newtonian gravity, that allows for an effective field description where Newtonian theory is “bootstrapped" introducing post-Newtonian corrections, providing a useful tool for calculations. Finally, we show that a logarithmic potential arises as a solution of the Bootstrapped field equation, in accordance with MOND prediction.

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.

Le Modèle Standard de la cosmologie décrit la formation des structures à grande échelle dans l'Univers récent dans un cadre quasi–newtonien. Ce modèle requiert la présence de composantes inconnues, la Matière Noire et l'Énergie Noire, afin de vérifier correctement les observations. Ces deux quantités représentent à elles seules près de 95% du contenu de l'Univers. Bien que ces composantes sombres soient activement recherchées par la communauté scientifique, il existe plusieurs alternatives qui tentent de traiter le problème des structures à grande échelle. Les théories inhomogènes décrivent l'impact des fluctuations cinématiques sur le comportement global de l'Univers. D'autres théories proposent également d'aller au-delà de la relativité générale. Durant cette thèse, j'ai mis au point des éléments clés d'une théorie lagrangienne totalement relativiste de la formation des structures. Supposant un feuilletage particulier de l'espace–temps j'ai résolu le système d'équations du premier ordre afin d'obtenir des solutions décrivant l'évolution de la matière dans un espace à la géométrie perturbée. J'ai également développé un schéma de résolution pour les ordres supérieurs de perturbation ainsi que leurs équivalent newtoniens. Une autre partie de ce travail de thèse consiste en le développement de quelques applications directes : la description d'un Univers silencieux ou l'hypothèse de courbure de Weyl et le problème de 'entropie gravitationnelle. Les objectifs à plus ou moins court terme seraient d'obtenir la description d'observables physiques and le développement d'autres applications. Cette étape de développement sera une interaction entre approches théorique et numérique et requerra de se rapprocher fortement des observateurs
The standard model of cosmology describes the formation of large scale structures in the late Universe within a quasi–Newtonian theory. This model requires the presence of unknown compounds of the Universe, Dark Matter and Dark Energy, to properly fit the observations. These two quantities, according to the Standard Model, represent almost 95% of the content of the Universe. Although the dark components are searched for by the scientific community, there exist several alternatives which try to deal with the problem of the large scale structures. Inhomogeneous theories describe the impact of the kinematical fluctuations on the global behaviour of the Universe. Or some theories proposed to go beyond general relativity. During my Ph.D. thesis, I developed key–elements of a fully relativistic Lagrangian theory of structure formation. Assuming a specific space–time slicing, I solved the first order system of equations to obtain solutions which describe the matter evolution within the perturbed geometry, and I developed higher order schemes and their correspondences with the Lagrangian perturbation solutions in the Newtonian approach. I also worked on some applications of these results like the description of a silent Universe or the Weyl curvature hypothesis and the problem of gravitational entropy. Further objectives are the description of physical observables and the development of direct applications. Next step of the development is an interaction between theoretical and numerical approaches, a study which would require strong cooperation with observers

Diss. (sammanfattning) Stockholm : Stockholms universitet, 2010.
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 5: Accepted. Paper 6: Submitted. Härtill 6 uppsatser.

We are at the dawn of a data-driven era in astrophysics and cosmology. A large number of ongoing and forthcoming experiments combined with an increasingly open approach to data availability offer great potential in unlocking some of the deepest mysteries of the Universe. Among these is understanding the nature of dark matter (DM)—one of the major unsolved problems in particle physics. Characterizing DM through its astrophysical signatures will require a robust understanding of its distribution in the sky and the use of novel statistical methods.

The first part of this thesis describes the implementation of a novel statistical technique which leverages the “clumpiness” of photons originating from point sources (PSs) to derive the properties of PS populations hidden in astrophysical datasets. This is applied to data from the Fermi satellite at high latitudes (|b| ≥ 30°) to characterize the contribution of PSs of extragalactic origin. We find that the majority of extragalactic gamma-ray emission can be ascribed to unresolved PSs having properties consistent with known sources such as active galactic nuclei. This leaves considerably less room for significant dark matter contribution.

The second part of this thesis poses the question: “what is the best way to look for annihilating dark matter in extragalactic sources?” and attempts to answer it by constructing a pipeline to robustly map out the distribution of dark matter outside the Milky Way using galaxy group catalogs. This framework is then applied to Fermi data and existing group catalogs to search for annihilating dark matter in extragalactic galaxies and clusters.

In this thesis I show how large galaxy surveys, in particular the study of the properties of galaxies, can shed light on gravitational wave sources and dark matter. This is achieved using the latest data from the Dark Energy Survey, an on-going 5000 deg2 optical survey. Galaxy properties such as photometric redshifts and stellar masses are derived through spectral energy distribution fitting methods. The results are used to study host galaxies of gravitational wave events and how light traces dark matter in galaxy clusters. Gravita- tional wave (GW) science, and particularly the electromagnetic follow up of these events, is transforming what had never been seen into a new astronomical field able to unveil the nature of cataclysmic events. Identifying the galaxies that host these events, and es- timating their redshift, stellar mass, and star–formation rate, is crucial for cosmological analysis with gravitational waves, for follow up studies and to understand the formation of the binary systems that are thought to produce observable gravitational wave signals. This thesis describes how the host matching is implemented within the DES–GW pipeline and how observations of NGC 4993, the galaxy host of the event GW170817, provide important information about possible formation scenarios for binary neutron stars. In particular, we find that NGC 4993 presents shell structures and we relate their formation to the binary formation. The same galaxy properties are used to derive an observable mass proxy for galaxy clusters. I show that this mass observable correlates well with the total mass of clusters, which is mainly composed of dark matter. It can therefore be used for cosmological studies with galaxy clusters. The measurement of stellar–to–halo mass relations in clusters provides insights on the connection between the star content and the total matter content in clusters, and how this evolves over cosmic time.

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.

A model of dark matter excitations is studied in an attempt to explain the anomalously large 511 keV photon line emission observed by the SPI spectrograph on INTEGRAL to be originating from the galactic bulge of the Milky Way. The proposed dark matter WIMP has a near degenerate mass partner a few MeV heavier. Scattering between dark matter particles leads to excitations, with the subsequent decays producing an electron-positron pair. In this way, the kinetic energy of the massive dark matter particles can be efficiently converted into electron-positron pairs moving slow enough to produce the narrow annihilation line observed. With a sufficiently large mass gap, kinematic considerations and the cuspy dark matter density profile constrain excitations to the galactic bulge where the escape velocity, and thus the fraction of dark matter particles above the kinematic cutoff, is large.
Un model d'excitations matière sombre est etudié dans une tentative d'explication de la ligne d'emission anormalement large observé par le spectrographe SPI sur INTEGRAL originaire du bulbe galactique de la Voie Lactée. La matière sombre WIMP proposée possède un partenaire ayant une masse de quelques MeV supplémentaires. La diffusion entre les particules de matière sombre mène aux excitations et à la désintégration ultérieure en une paire électron-positron. De cette façon, l'énergie cinétique des particules de matière sombre peut être convertie en paires électron-positron se déplaçant suffisement lentement pour produire l'étroite ligne d'annihilation observée. Avec un espacement en masse suffisement grand, les considérations cinématique et un profil de densité de la matière sombre cuspy contraignent les excitations au bulbe galactique, où la vitesse d'échappement, et donc la fraction de particules matière sombre au-dessus du seuil cinétique, est grande.

>Magister Scientiae - MSc
The growth of structure in the Universe proceeds via the collapse of dark matter and baryons. This process is retarded by dark energy which drives an accelerated expansion of the late Universe. In this thesis we use cosmological perturbation theory to investigate structure formation for a particular class of dark energy models, i.e. interacting dark energy models. In these models there is a non-gravitational interaction between dark energy and dark matter, which alters the standard evolution (with non-interacting dark energy) of the Universe. We consider a simple form of the interaction where the energy exchange in the background is proportional to the dark energy density. We analyse the background dynamics to uncover the e ect of the interaction. Then we develop the perturbation equations that govern the evolution of density perturbations, peculiar velocities and the gravitational potential. We carefully account for the complex nature of the perturbed interaction, in particular for the momentum transfer in the dark sector. This leads to two di erent types of model, where the momentum exchange vanishes either in the dark matter rest-frame or the dark energy rest-frame. The evolution equations for the perturbations are solved numerically, to show how structure formation is altered by the interaction.

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.

Hints of direct detection of dark matter have been presented by the DAMA, CoGeNT, and CRESST collaborations, despite a number of null results that seem to contradict such claims. Although standard spin-independent dark matter is not capable of reconciling the results, dark matter models containing isospin-violating couplings have shown promise in solving the issues surrounding direct detection of dark matter. Inelastic or momentum-dependent scattering dark matter has also been shown to help alleviate these tensions. In light of the 2012 XENON100 observations, updated analysis of surface event contamination at CoGeNT, revision of the energy resolution employed by XENON10, and new results from the CDMS-II silicon detectors, we study the extent to which spin-independent, spin-dependent, and combined models of isospin-violating dark matter are capable of explaining current direct detection data. Moreover, we explore the effect of an energy-dependent sodium quenching factor $Q_{\rm Na}$ for fitting the DAMA observations, and give an isospin-violating prediction for XENON1T. In addition to the usual analysis involving phase space plots, we investigate a halo-independent model of dark matter in the space of minimum velocities required for a dark matter particle to scatter off a given nucleus. For the first time, such an analysis is performed for models of dark matter which embrace both inelastic and isospin-violating couplings, as well as for dark matter with momentum- and spin dependent interactions. With respect to the models considered herein, our results do not support a dark matter interpretation of direct detection data in either the standard or halo-independent formalisms.
Conseils de détection directe de la matière noire ont été présentés par les DAMA, CoGeNT, et CRESST collaborations, malgré un certain nombre de résultats nuls qui semblent contredire ces allégations. Bien que la norme matière noire indépendante du spin n'est pas capable de concilier la résultats, la matière noire modèles contenant couplages de isospin-violation ont montré des résultats prometteurs dans résolution des problèmes de détection directe de la matière noire. Diffusion inélastique ou dynamique dépendant de la matière noire a également été démontré que aider à atténuer ces tensions. À la lumière des observations XENON100 2012, analyse actualisée de la contamination de l' événement de surface à CoGeNT, la révision de la résolution de l'énergie utilisée par XENON10, et de nouveaux résultats provenant des détecteurs de silicium CDMS-II, nous étudier la mesure dans laquelle indépendante du spin, dépendant du spin, et des modèles combinés de la matière noire isospin-violation sont capables d'expliquer les données de détection directs actuels. De plus, nous explorons l'effet d'une trempe de sodium dépendant de l'énergie facteur $Q_{\rm Na}$ pour le montage des observations DAMA, et de donner une prévision de isospin-violation de XENON1T. En plus de l'analyse habituelle impliquant des parcelles de l'espace de phase, nous étudions un modèle de halo-indépendant de la matière noire dans l'espace des vitesses minimales requises pour une particule de matière noire se disperser hors d'un noyau donné. Pour la première fois, une telle analyse est effectuée pour les modèles de matière noire qui embrassent les deux couplages élastiques et isospin-violation, ainsi que de la matière noire avec des interactions dépendant du dynamique et spin. En ce qui concerne les modèles considérés ici, nos résultats ne soutiennent pas une question d'interprétation sombre de données de détection directe soit dans la norme ou formalismes halo-indépendant.

In this thesis we investigate a possible formation mechanism of non-linear structures, such as primordial black holes or similar screened objects, within a modified gravity framework. In particular, these structures can form during radiation era and provide the current dark matter component of the Universe. We refer to a model consisting of a long range attractive fifth-force stronger than gravity, mediated by a light scalar field $\phi$ - which could be in principle dynamical dark energy of Coupled Quintessence - interacting with a non-relativistic $\psi$-particle. The latter is coupled to radiation and matter species only via usual gravity. By means of a dynamical system approach, we select the unique stable scaling solution of the phase space providing a radiation dominated era. Besides, after the introduction of the cosmological perturbation theory, we study the non-linear growth of the $\psi$ field density fluctuations in this epoch. The latter, being enhanced by the fifth interaction, in view of a field theory screening mechanisms that suppress the additional interaction, eventually collapse in stable and virialized structures, namely dark matter halos. We compare the theoretical predictions on the radius and the mass of the halos with experimental constraints on primordial black holes abundances, with an emphasis on their lensing signature in the solar mass window. In conclusion, we outline a viable scenario where the missing dark matter component of the universe might be completely supplied in form of dark halos.

In this work, we consider two different models of dark matter and set limits on results of experiments. One is a dynamic dark matter scenario where we put limits on parameters observable by experiments DAMA and XMASS through nuclear recoil of detector atoms (direct detection). The second is a case of dark matter annihilation into positrons and electrons and the signal this would produce on measured values of positron flux and ratio of electron to positron (indirect detection). The values of these quantities as measured by FERMI and PAMELA experiments are observed and an explanation using a dark matter annihilation is presented vs astrophysical sources of particles.

We explore a dynamic dark matter scenario with an ensemble of dark matter particles that starts at m₀ and spans a comb of particles separated by j^δΔ m. We verify the model by using Δm = ∞ and comparing the predictions to a non dynamic model for the same mass m0. We then observe the wider set of possibilities available with the dynamic dark matter model compared with the single mass case vis a vis constraints set by NaI and Xe detectors published by the DAMA and XMASS collaborations and check for validity of model against these measurements.

The Fermi experiment has measured the cosmic ray electron+positron spectrum and positron fraction [фe+/(фe⁺+e⁻)], and PAMELA has measured the positron fraction with better precision. While the majority of cosmic ray electrons and positrons are of astrophysical origin, there may also be a contribution from dark matter annihilation in the galactic halo. The upcoming results of the AMS experiment will show measurements of these quantities with far greater precision. One dark matter annihilation scenario is where two dark matter particles annihilate directly to e ⁺ and e⁻ final states. In this article, we calculate the signature “bumps” in these measurements assuming a given density profile (NFW profile). If the dark matter annihilates to electrons and positrons with a cross section σv ∼ 10⁻²⁶ cm³/s or greater, this feature may be discernible by AMS. However, we demonstrate that such a prominent spectral feature is already ruled out by the relative smoothness of the positron + electron cosmic ray spectrum as measured by Fermi. Hence we conclude that such a feature is undetectable unless the mass is less than ∼40 GeV.

In the standard model of cosmology, the universe is currently dominated by dark energy in the form of the cosmological constant that drives the expansion to accelerate. While the cosmological constant hypothesis is consistent with all current data, models with dynamical behaviour of dark energy are still allowed by observations. Uncertainty also remains over whether the underlying assumption of a homogeneous and isotropic universe is valid, or if large-scale inhomogeneities in the matter distribution can be the cause of the apparent late-time acceleration.This thesis investigates inhomogeneous cosmological models in which dark energy clusters or where we live inside an underdense region in a matter-dominated universe. In both of these scenarios, we expect directional dependences in the redshift-luminosity distance relation of type Ia supernovae. Dynamical models of dark energy predict spatial variations in the dark energy density. Searches for angular correlated fluctuations in the supernova peak magnitudes, as expected if dark energy clusters, yield results consistent with no dark energy fluctuations. However, the current observational limits on the amount of correlation still allow for quite general dark energy clustering occurring in the linear regime. Inhomogeneous models where we live inside a large, local void in the matter density can possibly explain the apparent acceleration without invoking dark energy. This scenario is confronted with current cosmological distance measurements to put constraints on the size and depth of the void, as well as on our position within it. The model is found to explain the observations only if the void size is of the order of the visible universe and the observer is located very close to the center, in violation of the Copernican principle.
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 4: Accepted.

This thesis is devoted to the study of phaenomenology within the quest for Dark Energy (DE) nature. Nowadays, thanks to the accuracy with which cosmological parameters have been constrained, Cosmology has really turned into a high precision science. In spite of their accuracy, however, data are still far from really constraining DE nature, so that this keeps perhaps the main puzzle in today’s cosmology. Constraints on DE, until now, came from measurements of the Cosmic Microwave Background (CMB), from the Hubble diagram of SupernovæIa, from deep galaxy samples and from a few other observables, as Lyα clouds, galaxy cluster distribution, etc. Such measures will be certainly extended and improved in the next decade(s) leading to more stringent constraints. Even more effective are however expected to be future weak lensing (WL) data, namely in combination with the above classical observables, marking a real turning point to Cosmology. This thesis wants to add a brick to the construction of this wide building, trying to study the impact of tomographic WL measurements on constraining dynamical and/or coupled DE models. Within this context, it will be outlined how massive neutrinos, added to the total cosmological energy balance, allow the consistency with present data of a higher DM–DE coupling. This last issue outlines how tomographic WL observables will allow to shed new light over a problem as neutrino masses, so enriching the patterns through which large scale data influence microphysical issues.

The LHC at CERN is now undergoing a set of upgrades to increase the center of mass energy for the colliding particles to be able to explore new physical processes. The focus of this thesis lies on the so called phase II upgrade which will preliminarily be completed in 2023. After the upgrade the LHC will be able to accelerate proton beams to such a velocity thateach proton has a center of mass energy of 14 TeV. One disadvantage of the upgrade is that it will be harder for the atlas detector to isolate unique particle collisions since more and more collisions will occur simultaneously, so called pile-up. For 14 TeV there does not exist a full simulation of the atlas detector. This thesis instead uses data from Monte Carlo simulations for the particle collisions and then uses so called smearing functions to emulate the detector responses. This thesis focuses on how a mono-jet analysis looking for different wimp models of dark matter will be affected by this increase in pile-up rate. The signal models which are in focus are those which try to explain dark matter without adding new theories to the standard model or QFT, such as the effective theory D5 operator and light vector mediator models. The exclusion limits set for the D5 operators mass suppression scale at 14 TeV and 1000 fb-1are 2-3 times better than previous results at 8 TeV and 10 fb-1. For the first time limits have been set on which vector mediator mass models can be excluded at 14 TeV.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
Na última década várias observações indicam que o universo está expandindo aceleradamente. Essa expansão acelerada pode ser explicada em um universo composto de 70% de energia escura e 30% de matéria (25% de matéria escura e 5% de matéria bariônica). A energia escura proporciona a pressão negativa necessária para produzir a aceleração em grandes escalas. Nesse trabalho faz-se uma revisão do modelo de um campo escalar como fonte da energia escura, conhecido genericamente como modelo de quintessência. Estuda-se o modelo de quintessência acoplada à matéria escura
In the previous decade many observations indicate that the universe is accelerating. This rapid expansion can be explained in an universe made up of 70% of dark energy and 30% of matter (25% of dark matter and 5% of baryonic matter). The dark energy provides negative pressure to produce acceleration. In this work it is studied the model of Quintessence, a model of scalar field, as source of the dark energy. It is studied the model of Coupled Quintessence with dark matter

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 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.

Cosmology is the science that studies the Universe as whole, aiming to understand its origin, composition and evolution. During the last decades, cosmology has transitioned from a “data staved” to a “data driven” science, inaugurating what is known as precision cosmology. This huge observational effort has confirmed and fostered theoretical research, and established the standard model of cosmology: Lambda-Cold Dark Matter (LCDM). This model successfully reproduces most of the observations. However, there are some persistent tensions between experiments that might be smoking guns of new physics beyond this model. Anyways, there is a difference between modeling and understanding, and LCDM is a phenomenological model that, for instance, does not describe the nature of the dark matter or dark energy. This thesis collects part of my research focused on pushing the limits of the standard cosmological model and its assumptions, regarding also existing tensions between experiments. New strategies to optimize the performance of future experiments are also proposed and discussed. The largest existing tension is between the direct measurements of the Hubble constant using the distance ladder in the local Universe and the inferred value obtained from observations of the Cosmic Microwave Background when LCDM is assumed. A model independent reconstruction of the late-time expansion history of the Universe is carried out, which allows us to identify possible sources and solutions of the tension. We also introduce the concept of the low redshift standard ruler, and measure it in a model independent way. Finally, we introduce a statistical methodology to analyze several data sets in a conservative way, no matter the level of discrepancy between them, accounting for the potential presence of systematic errors. The role of primordial black holes as candidates for dark matter is addressed in this thesis, too. Concretely, the impact of an abundant population of primordial black holes in the rest of cosmological parameters is discussed, considering also populations with extended mass distributions. In addition, massive primordial black holes might be the seeds that are needed to explain the origin of the supermassive black holes located in the center of the galaxies. We predict the contribution of a population of massive primordial black holes to the 21 cm radiation from the dark ages. This way, observations of the 21 cm intensity mapping observations of the dark ages could be used to ascertain if the seeds of the supermassive black holes are primordial. Finally, we estimate the potential of radio-continuum galaxy surveys to constrain LCDM. These kind of experiments can survey the sky quicker than spectroscopic and optical photometric surveys and cover much larger volumes. Therefore, they will be specially powerful to constrain physics which has impact on the largest observable scales, such as primordial non Gaussianity. On the other hand, intensity mapping experiments can reach higher redshifts than galaxy surveys, but the cosmological information of this signal is coupled with astrophysics. We propose a methodology to disentangle astrophysics and optimally extract cosmological information from the intensity mapping spectrum. Thanks to this methodology, intensity mapping will constrain the expansion history of the Universe up to reionization, as shown in this thesis.
El modelo estándar de cosmología, LCDM, se apoya en una cantidad ingente de observaciones extremadamente precisas, que es capaz de reproducir con gran exactitud. Sin embargo, este es un modelo fenomenológico que no es capaz de responder algunas de las preguntas fundamentales sobre el Universo, como la naturaleza de la materia oscura o la energía oscura. Además, cuando este modelo se utiliza para interpretar las observaciones, aparecen tensiones entre experimentos independientes. Estas tensiones, en el caso de no estar producidas por errores sistemáticos no tenidos en cuenta, necesitarían un modelo cosmológico diferente para ser resueltas. Esta tesis recoge trabajos publicados en revistas científicas investigando estos problemas de LCDM. Concretamente, se cubren tres temas principales: la tensión en la constante de Hubble entre las medidas directas usando la escalera de distancias y los valores inferidos a partir de las observaciones de la colaboración Planck asumiendo LCDM; el rol de los agujeros negros primordiales como semillas de los agujeros negros supermasivos, o como candidato para conformar una parte significativa de la materia oscura; y el potencial y las estrategias óptimas a aplicar en experimentos que mapean la estructura a gran escala del Universo para examinar LCDM y medir posibles desviaciones del modelo. De este modo, el trabajo aquí recogido tiene como objetivo investigar las tensiones presentes en LCDM, así como las preguntas que deja sin responder de una manera crítica y desde un punto de vista agnóstico. Además, pretende sentar las bases para futuras investigaciones en estas líneas, cuando estén disponibles nuevas y mejores observaciones, e indicar el camino para poder poner a prueba el modelo estándar de cosmología en los años venideros en regímenes en los que aún no se ha hecho ninguna medida.

The quest for the first detection of a galaxy cluster in the high energy gamma-ray regime is ongoing, and even though clusters are observed in several other wave-bands, there is still no firm detection in gamma-rays. To complement the observational efforts we estimate the gamma-ray contributions from both annihilating dark matter and cosmic-ray (CR) proton as well as CR electron induced emission. Using high-resolution simulations of galaxy clusters, we find a universal concave shaped CR proton spectrum independent of the simulated galaxy cluster. Specifically, the gamma-ray spectra from decaying neutral pions, which are produced by CR protons, dominate the cluster emission. Furthermore, based on our derived flux and luminosity functions, we identify the galaxy clusters with the brightest galaxy clusters in gamma-rays. While this emission is challenging to detect using the Fermi satellite, major observations with Cherenkov telescopes in the near future may put important constraints on the CR physics in clusters. To extend these predictions, we use a dark matter model that fits the recent electron and positron data from Fermi, PAMELA, and H.E.S.S. with remarkable precision, and make predictions about the expected gamma-ray flux from nearby clusters. In order to remain consistent with the EGRET upper limit on the gamma-ray emission from Virgo, we constrain the minimum mass of substructures for cold dark matter halos. In addition, we find comparable levels of gamma-ray emission from CR interactions and dark matter annihilations without Sommerfeld enhancement.
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Accepted.

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.

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 5: Manuscript. Paper 6: Manuscript.

Philosophiae Doctor - PhD
Numerical simulations play a crucial role in testing current cosmological models of the formation and evolution of the cosmic structure observed in the modern Universe. Simulations of the collapse of both baryonic and non-baryonic matter under the influence of gravity have yielded important results in our understanding of the large scale structure of the Universe. In addition to the underlying large scale structure, simulations which include gas dynamics can give us valuable insight into, and allow us to make testable predictions on, the nature and distribution of baryonic matter on a wide range of scales. In this work we give an overview of cosmological simulations and the methods employed in the solution of many body problems. We then present three projects focusing on scales ranging from individual galaxies to the cosmic web connecting clusters of galaxies thereby demonstrating the potential and diversity of numerical simulations in the fields of cosmology and astrophysics. We firstly investigate the environmental dependance of neutral hydrogen in the intergalactic medium by utilising high resolution cosmological hydrodynamic simulations in Chapter 3. We find that the extent of the neutral hydrogen radial profile is dependant on both the environment of the galaxy and its classification within the group ie. whether it is a central or satellite galaxy. We investigate whether this effect could arise from ram pressure forces exerted on the galaxies and find good agreement between galaxies experiencing high ram pressure forces and those with a low neutral hydrogen content. In Chapter 4 we investigate the velocity–shape alignment of clusters in a dark matter only simulation and the effect of such an alignment on measurements of the kinetic Sunyaev–Zeldovich (kSZ) effect. We find an alignment not only exists but can lead to an enhancement in the kSZ signal of up to 60% when the cluster is orientated along the line-of-sight. Finally we attempt to identify shocked gas in clusters and filaments using intermediate resolution cosmological hydrodynamic simulations in Chapter 5 with a view to predicting the synchrotron emission from these areas, something that may be detectable with the Square Kilometer Array.

We derive the stellar mass fraction in the galaxy cluster RXC J2248.7-4431 observed with the Dark Energy Survey (DES) during the Science Verification period. We compare the stellar mass results from DES (five filters) with those from the Hubble Space Telescope Cluster Lensing And Supernova Survey (CLASH; 17 filters). When the cluster spectroscopic redshift is assumed, we show that stellar masses from DES can be estimated within 25 per cent of CLASH values. We compute the stellar mass contribution coming from red and blue galaxies, and study the relation between stellar mass and the underlying dark matter using weak lensing studies with DES and CLASH. An analysis of the radial profiles of the DES total and stellar mass yields a stellar-to-total fraction of f(star) = (6.8 +/- 1.7) x 10(-3) within a radius of r(200c) similar or equal to 2 Mpc. Our analysis also includes a comparison of photometric redshifts and star/galaxy separation efficiency for both data sets. We conclude that space-based small field imaging can be used to calibrate the galaxy properties in DES for the much wider field of view. The technique developed to derive the stellar mass fraction in galaxy clusters can be applied to the similar to 100 000 clusters that will be observed within this survey and yield important information about galaxy evolution.

Les preuves pour l'existence de la matière noire (MN), sous forme d'une particule inconnue qui rempli les halos galactiques, sont issues d'observations astrophysiques et cosmologiques: son effet gravitationnel est visible dans les rotations des galaxies, des amas de galaxies et dans la formation des grandes structures de l'univers. Une manifestation non-gravitationnelle de sa présence n'a pas encore été découverte. L'une des techniques les plus prometteuse est la détection indirecte de la MN, consistant à identifier des excès dans les flux de rayons cosmiques pouvant provenir de l'annihilation ou la désintégration de la MN dans le halo de la Voie Lactée. Les efforts expérimentaux actuels se focalisent principalement sur une gamme d'énergie de l'ordre du GeV au TeV, où un signal de WIMP (Weakly Interacting Massive Particles) est attendu. L'analyse des mesures récentes et inédites des rayons cosmiques chargés (antiprotons, électrons et positrons) et leurs émissions secondaires et les améliorations des modèles astrophysiques sont présentées.Les données de PAMELA sur les antiprotons contraignent l'annihilation et la désintégration de la MN de manière similaire (et même légèrement meilleurs) que les contraintes les plus fortes venant des rayons gamma, même dans le cas où les énergies cinétiques inférieures à 10 GeV sont écartées. En choisissant des paramètres astrophysiques différents (modèles de propagation et profils de MN), les contraintes peuvent changer d'un à deux ordres de grandeur. Pour exploiter la totalité de la capacité des antiprotons à contraindre la MN, des effets précédemment négligés sont incorporés et se révèlent être importants dans l'analyse des données inédites de AMS-02 : ajouter les pertes d'énergie, la diffusion dans l'espace des moments et la modulation solaire peut modifier les contraintes, même à de hautes masses. Une mauvaise interprétation des données peut survenir si ces effets ne sont pas pris en compte. Avec les flux de protons et d'hélium exposé par AMS-02, le fond astrophysique et ces incertitudes du ratio antiprotons sur protons sont réévalués et comparés aux données inédites de AMS-02. Aucune indication pour un excès n'est trouvé. Une préférence pour un halo confinant plus large et une dépendance en énergie du coefficient de diffusion plus plate apparaissent. De nouvelles contraintes sur l'annihilation et la désintégration de la MN sont ainsi dérivés.Les émissions secondaires des électrons et des positrons peuvent aussi contraindre l'annihilation et la désintégration de la MN dans le halo galactique : le signal radio dû à la radiation synchrotron des électrons et positrons dans le champs magnétique galactique, les rayons gamma des processus de bremsstrahlung avec le gas galactique et de Compton Inverse avec le champs radiatif interstellaire sont considérés. Différentes configurations de champs magnétique galactique et de modèles de propagation et des cartes de gas et de champs radiatif interstellaire améliorés sont utilisées pour obtenir des outils permettant le calculs des émissions synchrotrons et bremsstrahlung venant de MN de type WIMP. Tous les résultats numériques sont incorporés dans la dernière version du Poor Particle Physicist Coookbook for DM Indirect Detection (PPPC4DMID).Une interprétation d'un possible excès dans les données de rayons gamma de Fermi-LAT au centre galactique comme étant dû à l'annihilation de MN en canaux hadronique et leptonique est analysée. Dans une approche de messagers multiples, le calcul des émissions secondaires est amélioré et se révèle être important pour la détermination du spectre pour le canal leptonique. Ensuite, les limites provenant des antiprotons sur l'annihilation en canal hadronique contraignent sévèrement l'interprétation de cet excès comme étant dû à la MN, dans le cas de paramètres de propagation et de modulation solaire standards. Avec un choix plus conservatif de ces paramètres elles s'assouplissent considérablement
Overwhelming evidence for the existence of Dark Matter (DM), in the form of an unknownparticle filling the galactic halos, originates from many observations in astrophysics and cosmology: its gravitational effects are apparent on galactic rotations, in galaxy clusters and in shaping the large scale structure of the Universe. On the other hand, a non-gravitational manifestation of its presence is yet to be unveiled. One of the most promising techniques is the one of indirect detection, aimed at identifying excesses in cosmic ray fluxes which could possibly be produced by DM annihilations or decays in the Milky Way halo. The current experimental efforts mainly focus in the GeV to TeV energy range, which is also where signals from WIMPs (Weakly Interacting Massive Particles) are expected. Focussing on charged cosmic rays, in particular antiprotons, electrons and positrons, as well as their secondary emissions, an analysis of current and forseen cosmic ray measurements and improvements on astrophysical models are presented. Antiproton data from PAMELA imposes contraints on annihilating and decaying DM which are similar to (or even slightly stronger than) the most stringent bounds from gamma ray experiments, even when kinetic energies below 10 GeV are discarded. However, choosing different sets of astrophysical parameters, in the form of propagation models and halo profiles, allows the contraints to span over one or two orders of magnitude. In order to exploit fully the power of antiprotons to constrain or discover DM, effects which were previously perceived as subleading turn out to be relevant especially for the analysis of the newly released AMS-02 data. In fact, including energy losses, diffusive reaccelleration and solar modulation can somewhat modify the current bounds, even at large DM masses. A wrong interpretation of the data may arise if they are not taken into account. Finally, using the updated proton and helium fluxes just released by the AMS-02 experiment, the astrophysical antiproton to proton ratio and its uncertainties are reevaluated and compared to the preliminarly reported AMS-02 measurements. No unambiguous evidence for a significant excess with respect to expectations is found. Yet, some preference for thicker halos and a flatter energy dependence of the diffusion coefficient starts to emerge. New stringed constraints on DM annihilation and decay are derived. Secondary emissions from electrons and positrons can also be used to constrain DM annihilation or decay in the galactic halo. The radio signal due to synchrotron radiation of electrons and positrons on the galactic magnetic field, gamma rays from bremsstrahlung processes on the galactic gas densities and from Inverse Compton scattering processes on the interstellar radiation field are considered. With several magnetic field configurations, propagation scenarios and improved gas density maps and interstellar radiation field, state-of-art tools allowing the computaion of synchrotron and bremssttrahlung radiation for any WIMP DM model are provided. All numerical results for DM are incorporated in the release of the Poor Particle Physicist Coookbook for DM Indirect Detection (PPPC4DMID). Finally, the possible GeV gamma-ray excess identified in the Fermi-LAT data from the Galactic Center in terms of DM annihilation, either in hadronic or leptonic channels is studied. In order to test this tantalizing interprestation, a multi-messenger approach is used: first, the computation of secondary emisison from DM with respect to previous works confirms it to be relevant for determining the DM spectrum in leptonic channels. Second, limits from antiprotons severely constrain the DM interpretation of the excess in the hadronic channel, for standard assumptions on the Galactic propagation parameters and solar modulation. However, they considerably relax if more conservative choices are adopted

Aglomerados de galáxias são as maiores estruturas no Universo. Sua distribuição mapeia os halos de matéria escura formados nos potenciais profundos do campo de matéria escura. Consequentemente, a abundância de aglomerados é altamente sensível a expansão do Universo, assim como ao crescimento das perturbações de matéria escura, constituindo uma poderosa ferramenta para fins cosmológicos. Na era atual de grandes levantamentos observacionais que produzem uma quantidade gigantesca de dados, as propriedades estatísticas dos objetos observados (galáxias, aglomerados, supernovas, quasares, etc) podem ser usadas para extrair informações cosmológicas. Para isso, é necessária o estudo da formação de halos de matéria escura, da detecção dos halos e aglomerados, das ferramentas estatísticas usadas para o vínculos de parâmetros, e finalmente, dos efeitos da detecções ópticas. No contexto da formulação da predição teórica da contagem de halos, foi analisada a influência de cada parâmetro cosmológico na abundância dos halos, a importância do uso da covariância dos halos, e a eficácia da utilização dos halos para vincular cosmologia. Também foi analisado em detalhes os intervalos de redshift e o uso de conhecimento prévio dos parâmetros ({\\it priors}). A predição teórica foi testada um uma simulação de matéria escura, onde a cosmologia era conhecida e os halos de matéria escura já haviam sido detectados. Nessa análise, foi atestado que é possível obter bons vínculos cosmológicos para alguns parâmetros (Omega_m,w,sigma_8,n_s), enquanto outros parâmetros (h,Omega_b) necessitavam de conhecimento prévio de outros testes cosmológicos. Na seção dos métodos estatísticos, foram discutidos os conceitos de {\\it likelihood}, {\\it priors} e {\\it posterior distribution}. O formalismo da Matriz de Fisher, bem como sua aplicação em aglomerados de galáxias, foi apresentado e usado para a realização de predições dos vínculos em levantamentos atuais e futuros. Para a análise de dados, foram apresentados métodos de Cadeias de Markov de Monte Carlo (MCMC), que diferentemente da Matriz de Fisher não assumem Gaussianidade entre os parâmetros vinculados, porém possuem um custo computacional muito mais alto. Os efeitos observacionais também foram estudados em detalhes. Usando uma abordagem com a Matriz de Fisher, os efeitos de completeza e pureza foram extensivamente explorados. Como resultado, foi determinado em quais casos é vantajoso incluir uma modelagem adicional para que o limite mínimo de massa possa ser diminuído. Um dos principais resultados foi o fato que a inclusão dos efeitos de completeza e pureza na modelagem não degradam os vínculos de energia escura, se alguns outros efeitos já estão sendo incluídos. Também foi verificados que o uso de priors nos parâmetros não cosmológicos só afetam os vínculos de energia escura se forem melhores que 1\\%. O cluster finder(código para detecção de aglomerados) WaZp foi usado na simulação, produzindo um catálogo de aglomerados. Comparando-se esse catálogo com os halos de matéria escura da simulação, foi possível investigar e medir os efeitos observacionais. A partir dessas medidas, pôde-se incluir correções para a predição da abundância de aglomerados, que resultou em boa concordância com os aglomerados detectados. Os resultados a as ferramentas desenvolvidos ao longo desta tese podem fornecer um a estrutura para a análise de aglomerados com fins cosmológicos. Durante esse trabalho, diversos códigos foram desenvolvidos, dentre eles, estão um código eficiente para computar a predição teórica da abundância e covariância de halos de matéria escura, um código para estimar a abundância e covariância dos aglomerados de galáxias incluindo os efeitos observacionais, e um código para comparar diferentes catálogos de halos e aglomerados. Esse último foi integrado ao portal científico do Laboratório Interinstitucional de e-Astronomia (LIneA) e está sendo usado para avaliar a qualidade de catálogos de aglomerados produzidos pela colaboração do Dark Energy Survey (DES), assim como também será usado em levantamentos futuros.
Abstract Galaxy clusters are the largest bound structures of the Universe. Their distribution maps the dark matter halos formed in the deep potential wells of the dark matter field. As a result, the abundance of galaxy clusters is highly sensitive to the expansion of the universe as well as the growth of dark matter perturbations, representing a powerful tool for cosmological purposes. In the current era of large scale surveys with enormous volumes of data, the statistical quantities from the objects surveyed (galaxies, clusters, supernovae, quasars, etc) can be used to extract cosmological information. The main goal of this thesis is to explore the potential use of galaxy clusters for constraining cosmology. To that end, we study the halo formation theory, the detection of halos and clusters, the statistical tools required to quarry cosmological information from detected clusters and finally the effects of optical detection. In the composition of the theoretical prediction for the halo number counts, we analyze how each cosmological parameter of interest affects the halo abundance, the importance of the use of the halo covariance, and the effectiveness of halos on cosmological constraints. The redshift range and the use of prior knowledge of parameters are also investigated in detail. The theoretical prediction is tested on a dark matter simulation, where the cosmology is known and a dark matter halo catalog is available. In the analysis of the simulation we find that it is possible to obtain good constraints for some parameters such as (Omega_m,w,sigma_8,n_s) while other parameters (h,Omega_b) require external priors from different cosmological probes. In the statistical methods, we discuss the concept of likelihood, priors and the posterior distribution. The Fisher Matrix formalism and its application on galaxy clusters is presented, and used for making forecasts of ongoing and future surveys. For the real analysis of data we introduce Monte Carlo Markov Chain (MCMC) methods, which do not assume Gaussianity of the parameters distribution, but have a much higher computational cost relative to the Fisher Matrix. The observational effects are studied in detail. Using the Fisher Matrix approach, we carefully explore the effects of completeness and purity. We find in which cases it is worth to include extra parameters in order to lower the mass threshold. An interesting finding is the fact that including completeness and purity parameters along with cosmological parameters does not degrade dark energy constraints if other observational effects are already being considered. The use of priors on nuisance parameters does not seem to affect the dark energy constraints, unless these priors are better than 1\\%.The WaZp cluster finder was run on a cosmological simulation, producing a cluster catalog. Comparing the detected galaxy clusters to the dark matter halos, the observational effects were investigated and measured. Using these measurements, we were able to include corrections for the prediction of cluster counts, resulting in a good agreement with the detected cluster abundance. The results and tools developed in this thesis can provide a framework for the analysis of galaxy clusters for cosmological purposes. Several codes were created and tested along this work, among them are an efficient code to compute theoretical predictions of halo abundance and covariance, a code to estimate the abundance and covariance of galaxy clusters including multiple observational effects and a pipeline to match and compare halo/cluster catalogs. This pipeline has been integrated to the Science Portal of the Laboratório Interinstitucional de e-Astronomia (LIneA) and is being used to automatically assess the quality of cluster catalogs produced by the Dark Energy Survey (DES) collaboration and will be used in other future surveys.

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.

The presence of dark matter is inferred at scales ranging from rotations of galaxies to imprints in the CMB – the Big Bang after-glow. The nature of dark matter is, however, still unknown as no detection other than the gravitational one has been made. This thesis presents two analyses searching for a neutrino signal from dark matter annihilations in the Milky Way. The first analysis searched for an excess of νμ charged current events with directions from the central region of the dark matter halo and, was focused on low energy events, thus probing low dark matter particle masses. Approximately 319 days of data collected with the 79-string configuration of the IceCube detector was used in the analysis. Despite a large deficit in the number of observed events the data were found to be consistent with background and upper limits were set on <σⱴ>. At the time of the analysis these limits were the strongest set by a neutrino experiment below 100 GeV. The second analysis was performed on a data sample originally used in an unfolding analysis of the atmospheric and astrophysical neutrino spectra. The data consisted of contained cascade events above 1 TeV collected with the 79-string configuration and the completed detector in the 86-string configuration during two years of data-taking. The limits set by this analysis were more constraining by up to a factor of 10 compared to previous IceCube analyses, and the most competitive limits are set assuming a Burkert halo profile. These two analyses prompted the development of a signal subtraction likelihood method to address the problem of signal contamination in background estimates based on scrambled data. Additionally a study concerning future extensions of IceCube in the Gen2 project is presented. The cascade reconstruction performance was examined and compared for different proposed detector extensions.

La materia ordinaria copre soli pochi punti percentuali della massa-energia totale dell'Universo, che è invece largamente dominata da componenti “oscure”. Il modello standard usato per descriverle è il modello LambdaCDM. Nonostante esso sembri consistente con la maggior parte dei dati attualmente disponibili, presenta alcuni problemi fondamentali che ad oggi restano irrisolti, lasciando spazio per lo studio di modelli cosmologici alternativi. Questa Tesi mira a studiare un modello proposto recentemente, chiamato “Multi-coupled Dark Energy” (McDE), che presenta interazioni modificate rispetto al modello LambdaCDM. In particolare, la Materia Oscura è composta da due diversi tipi di particelle con accoppiamento opposto rispetto ad un campo scalare responsabile dell'Energia Oscura. L'evoluzione del background e delle perturbazioni lineari risultano essere indistinguibili da quelle del modello LambdaCDM. In questa Tesi viene presentata per la prima volta una serie di simulazioni numeriche “zoomed”. Esse presentano diverse regioni con risoluzione differente, centrate su un singolo ammasso di interesse, che permettono di studiare in dettaglio una singola struttura senza aumentare eccessivamente il tempo di calcolo necessario. Un codice chiamato ZInCo, da me appositamente sviluppato per questa Tesi, viene anch'esso presentato per la prima volta. Il codice produce condizioni iniziali adatte a simulazioni cosmologiche, con differenti regioni di risoluzione, indipendenti dal modello cosmologico scelto e che preservano tutte le caratteristiche dello spettro di potenza imposto su di esse. Il codice ZInCo è stato usato per produrre condizioni iniziali per una serie di simulazioni numeriche del modello McDE, le quali per la prima volta mostrano, grazie all'alta risoluzione raggiunta, che l'effetto di segregazione degli ammassi avviene significativamente prima di quanto stimato in precedenza. Inoltre, i profili radiale di densità ottenuti mostrano un appiattimento centrale nelle fasi iniziali della segregazione. Quest'ultimo effetto potrebbe aiutare a risolvere il problema “cusp-core” del modello LambdaCDM e porre limiti ai valori dell'accoppiamento possibili.

Identifying the matter in the universe is one of the main challenges of modern cosmology and astrophysics. An important part of this matter seems to be made of non-baryonic particles. EDELWEISS is a direct dark matter search using cryogenic germanium bolometers in order to look for particles that interact very weakly with the ordinary matter, generically known as WIMPs. An important challenge for EDELWEISS is the radioactive background and one of the ways to identify it is to use a larger variety of target crystals. Sapphire is a light target which can be complementary to the germanium crystals already in use. Spectroscopic characterization studies have been performed using different sapphire samples in order to find the optimum doping concentration for good low temperature scintillation. Ti doped crystals with weak Ti concentrations have been used for systematic X ray excitation tests both at room temperature and down to 30 K. The tests have shown that the best Ti concentration for optimum room temperature scintillation is 100 ppm and 50 ppm at T = 45 K. All concentrations have been checked by optical absorption and fluorescence.
After having shown that sapphire had interesting characteristics for building heat-scintillation detectors, we have tested if using a sapphire detector was feasible within a dark matter search. During the first commissioning tests of EDELWEISS II, we have proved the compatibility between a sapphire heat-scintillation detector and the experimental setup.

Many astronomical observations, including rotational curve measurements of stars and the analysis of the cosmic microwave background, suggest the existence of an invisible matter density content in the Universe, commonly called Dark Matter (DM). Possibly, DM could be of particle nature, where Weakly Interacting Massive Particles (WIMPs) could be a viable DM candidate. The cubic-kilometer sized IceCube neutrino observatory located at the Earth’s South Pole can search indirectly for the existence of DM by detecting neutrino signals from WIMP self-annihilation in the Galactic center (GC) and the Galactic halo (GH). Two main physics analyses were developed and conducted to search indirectly for WIMP self-annihilation in the Milky Way’s GC and GH. Signal hypotheses for different WIMP annihilation channels, WIMP masses and DM halo profiles were tested. The results of both analyses were compatible with the background-only hypothesis for all tested signal hypotheses. Thus, upper limits at the 90% confidence level (C.L.) on the thermally averaged DM self-annihilation cross-section, <σΑv>, were set. Dedicated atmospheric muon veto techniques have been developed for the GC search making such an IceCube analysis possible for the first time. The GC analysis utilized data from 319.7 days of live-time of the IceCube detector running in its 79-string configuration during 2010 and 2011, whereas the GH analysis utilized pre-existing data samples developed for point-like neutrino sources with a live-time of 1701.9 days between 2008 and 2013. The most stringent upper limits on <σΑv> were obtained for WIMP annihilation directly into a pair of neutrinos assuming a Navarro-Frenk-White (NFW) DM halo profile. Conducting the GC and GH analyses for this annihilation channel an upper limit on <σΑv> as low as 4.0 · 10-24 cm3 s-1 and 4.5 · 10-24 cm3 s-1 is set for a 65 GeV and 500 GeV massive WIMP, respectively. These galactic indirect neutrino searches for DM are complementary to the indirect gamma-ray DM searches usually performed on extra-galactic targets like spheroidal dwarf galaxies.

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 2: Manuscript.

Descriveremo una teoria di gravità emergente, che ci permette sotto certe condizioni di identificare gli effetti gravitazionali della materia oscura come deformazioni del mezzo di energia oscura tramite elasticità lineare. Per fare ciò, descriveremo quantità necessarie e costanti in tre differenti capitoli. Nella prima parte rivisiteremo la teoria della gravitazione di Newton da un punto di vista classico della gravità basato sulla costante di gravitazione universale e sul potenziale gravitazionale. Nella seconda parte vedremo brevemente alcuni dei risultati principali in cosmologia moderna senza essere troppo specifici. Descriveremo alcuni fatti sperimentali come la velocità di rotazione delle galassie a spirale, che suggerisce l'esistenza della materia oscura. Spiegheremo in oltre il motivo per cui abbiamo bisogno di una scala di accelerazione come alternativa alle teorie sulla materia oscura e come le due possono congiungersi in gravità emergente. Nella terza parte daremo una rigorosa e al contempo elementare descrizione di elasticità lineare. Introdurremo i tensori di sforzo e stress, come sono legati fra di loro e vedremo anche alcuni importanti parametri che ci aiuteranno a descrivere il mezzo di energia oscura nei dettagli. Mostreremo l'esistenza di una direzione preferenziale nel mezzo di energia oscura che identifica una superficie di interfaccia dove tutte le identificazioni possono essere fatte. Nel capitolo finale uniremo finalmente tutte le nozioni date nei tre capitoli precedenti per formulare una semplice, ma allo stesso tempo completa descrizione della teoria, descrivendo i suoi punti forti e deboli. Una volta che abbiamo mostrato che le quantità gravitazionali ed elastiche sono relazionate sotto alcune condizioni nel mezzo di energia oscura, diventerà facile vedere la dualità fra certe leggi, specialmente dal punto di vista energetico.

What is the nature of the dark sector in the Universe? This is one of the most fundamental questions in modern cosmology. The so-called standard model of cosmology (ΛCDM) fails to reproduce some observational data and thus exploring potential alternative cosmologies is of great importance for cosmology. In this research I probe two potential alternative cosmologies, ΛWDM and dynamical dark energy models, using both strong and weak gravitational lensing. Gravitational lensing is a powerful probe of the distribution of matter including dark matter. The mass of dark matter particles in the ΛWDM cosmologies is on the order of ∼ keV and the density fluctuations are suppressed on small scales. The evolving dark energy cosmologies assume that the role of dark energy is played by a dynamical scalar field rather than a cosmological constant with a constant energy density. The structures in non-standard cosmologies form and evolve differently from those in the ΛCDM model, and thus the internal properties and abundance of (sub)structures are not the same. Consequently, the strong and weak gravitational lensing which probe the matter distribution will differ. I find that both strong and weak lensing can probe for the presence of Warm Dark Matter. WDM clusters have slightly larger Einstein radii and lensing cross-sections than their CDM counterparts. The higher lensing efficiency in WDM cosmologies is a result of the physical size of dark matter haloes and their internal properties. WDM substructures are more extended than CDM ones, and hence they significantly alter the size of critical lines and caustics. The WDM substructures can also boost the cross-section for multiple images. In addition, they have a significant impact on the magnification distribution. Although the slope of the magnification distribution is the same for both WDM and CDM cosmologies, there is an excess in the magnification distribution of WDM model relative to that of the CDM one. In addition, the area of high magnification in the weak lensing regions of WDM models is larger than that of CDM ones. The matter in WDM cosmologies is more homogeneously distributed than their CDM counterparts, and hence there would be more matter in the beam. I also find that the impact of WDM on the weak lensing signature can be explored by means of the observed number density of galaxies as well as the reconstruction of shear and convergence. However, I find that the latter method is more reliable. Despite the difficulties with the method used to reconstruct the convergence, the spatial distributions of the reconstructed convergence in the WDM and CDM models show that the matter in the WDM cosmology is more homogeneously distributed than that in the CDM one. Strong lensing analyses in dynamical dark energy cosmologies showed that the Einstein radius and cross-section of φCDM clusters do not differ significantly from those of the ΛCDM counterparts. The φCDM clusters cannot reproduce the observations of 12 MACS clusters in the literature and thus the φCDM model cannot resolve the arc statistics problem. In addition, the strong lensing efficiency of φ(β = 0.050)CDM clusters is higher than that of their ΛCDM counterparts and the observed MACS sample. However, one cannot argue that φ(β = 0.050)CDM clusters can resolve the arc statistics problem, at least from these suites of simulations, as their masses are significantly higher than those of the observed MACS clusters.

Modern Cosmology offers us a great understanding of the universe with striking precision, made possible by the modern technologies of the newest generations of telescopes. The standard cosmological model, however, is not absent of theoretical problems and open questions. One possibility that has been put forward is the existence of a coupling between dark sectors. The idea of an interaction between the dark components could help physicists understand why we live in an epoch of the universe where dark matter and dark energy are comparable in terms of energy density, which can be regarded as a strange coincidence given that their time evolutions are completely different. Dark matter and dark energy are generally treated as perfect fluids. Interaction is introduced when we allow for a non-zero term in the right-hand side of their individual energy-momentum tensor conservation equations. We proceed with a phenomenological approach to test models of interaction with observations of redshift-space distortions. In a flat universe composed only of these two fluids, we consider separately two forms of interaction, through terms proportional to the densities of both dark energy and dark matter. An analytic expression for the growth rate approximated as f = Omega^gamma, where Omega is the percentage contribution from the dark matter to the energy content of the universe and gamma is the growth index, is derived in terms of the interaction strength and of other parameters of the model in the first case, while for the second model we show that a non-zero interaction cannot be accommodated by the index growth approximation. The successful expressions obtained are then used to compare the predictions with growth of structure observational data in a Markov Chain Monte Carlo code and we find that the current growth data alone cannot impose constraints on the interaction strength due to their large uncertainties. We also employ observations of galaxy clusters to assess their virial state via the modified Layzer-Irvine equation in order to detect signs of an interaction. We obtain measurements of observed virial ratios, interaction strength, rest virial ratio and departure from equilibrium for a set of clusters. A compounded analysis indicates an interaction strength of 0.29^{+2.25}_{-0.40}, compatible with no interaction, but a compounded rest virial ratio of 0.82^{+0.13}_{-0.14}, which means a 2 sigma confidence level detection. Despite this tension, the method produces encouraging results while still leaves room for improvement, possibly by removing the assumption of small departure from equilibrium.
A cosmologia moderna oferece um ótimo entendimento do universo com uma precisão impressionante, possibilitada pelas tecnologias modernas das gerações mais novas de telescópios. O modelo cosmológico padrão, porém, não é livre de problemas do ponto de vista teórico, deixando perguntas ainda sem respostas. Uma possibilidade que tem sido proposta é a existência de um acoplamento entre setores escuros. A ideia de uma interação entre os componentes escuros poderia ajudar os físicos a entender por que vivemos em uma época do universo na qual a matéria escura e a energia escura são comparáveis em termos de densidades de energia, o que pode ser considerado uma estranha coincidência dado que suas evoluções com o tempo são completamente diferentes. Matéria escura e energia escura são geralmente tratadas como fluidos perfeitos. A interação é introduzida ao permitirmos um tensor não nulo no lado direito das equações de conservação dos tensores de energia-momento. Prosseguimos com uma abordagem fenomenológica para testar modelos de interação com observações de distorções no espaço de redshift. Em um universo plano composto apenas por esses dois fluidos, consideramos, separadamente, duas formas de interação, através de termos proporcionais às densidades de energia escura e de matéria escura. Uma expressão analítica para a taxa de crescimento aproximada por f = Omega^gamma, onde Omega é a contribuição percentual da matéria escura para o conteúdo do universo e gamma é o índice de crescimento, é deduzida em termos da interação e de outros parâmetros do modelo no primeiro caso, enquanto para o segundo caso mostramos que uma interação não nula não pode ser acomodada pela aproximação do índice de crescimento. As expressões obtidas são então utilizadas para comparar as previsões com dados observacionais de crescimento de estruturas em um programa para Monte Carlo via cadeias de Markov. Concluímos que tais dados atuais por si só não são capazes de restringir a interação devido às suas grandes incertezas. Utilizamos também observações de aglomerados de galáxias para analisar seus estados viriais através da equação de Layzer-Irvine modificada a fim de detectar sinais de interação. Obtemos medições de taxas viriais observadas, constante de interação, taxa virial de equilíbrio e desvio do equilíbrio para um conjunto de aglomerados. Uma análise combinada indica uma constante de interação 0.29^{+2.25}_{-0.40}, compatível com zero, mas uma taxa virial de equilíbrio combinada de 0.82^{+0.13}_{-0.14}, o que significa uma detecção em um intervalo de confiança de 2 sigma. Apesar desta tensão, o método produz resultados encorajadores enquanto ainda permite melhorias, possivelmente pela remoção da suposição de pequenos desvios do equilíbrio.

Per quanto la cosmologia osservativa odierna sia in una fase di precisione senza precedenti, con i dati CMB, BAO, e Supernovae Ia che mostrano di essere in accordo con l’attuale modello LCDM, i dati Planck sono in tensione con quelli a basso redshift, provenienti ad esempio dal misurazioni di weak lensing, che puntano verso un tasso più basso di crescita delle strutture. I modelli Dark Scattering qui trattati sono caratterizzati dalla evoluzione di un campo scalare classico con il ruolo di DE, e dalla interazione che le particelle di Materia Oscura (DM) hanno con questo campo. Considerando le particelle DM in moto attraverso il fluido DE, esse osservano un flusso di momento diverso da zero, indice di una forza proporzionale alla sezione d'urto di scattering tra DE e DM. Nel presente lavoro sono stati analizzati dati provenienti da simulazioni cosmologiche N-body DM-only per cinque modelli: due a equazione di stato DE costante, due con equazione di stato dipendente dal tempo, e infine il modello standard LCDM come base di confronto. Le condizioni iniziali sono uguali per tutti i modelli, in modo tale che ogni differenza rilevata nei risultati sia riconducibile agli effetti dei diversi modelli cosmologici. Sono stati ricavati i profili di densità e, per la prima volta su questi dati, i profili di velocità, di un significativo di aloni di materia oscura per ogni cosmologia, divisi in bin di massa e per tre redshift. Viene evidenziato come il termine aggiuntivo di drag nei modelli dark scattering abbia due effetti diversi nella crescita delle strutture. Nel regime lineare, infatti, le particelle DM in infall verso il centro degli ammassi hanno una direzione radiale del moto e l'attrito con il fluido DE le fa rallentare, diminuendo la loro velocità. Quando passano al regime non lineare, acquistano una componente tangenziale di velocità che di fatto fa sì che l'interazione con l'energia oscura provochi una perdita di energia cinetica con conseguente collasso più rapido.

This thesis deals with Composite Higgs (CH) models, dark matter and neutrino masses. In CH models, the Higgs is a pseudo-Goldstone boson of a high-energy strong dynamics. We construct CP-even and CP-odd bosonic effective chiral Lagrangian for a generic symmetric coset G/H. Assuming that the only sources of custodial symmetry are the ones present in the SM, we study the projection of this Lagrangian into the low-energy SM chiral Lagrangian. This is applied in three particular scenarios: the original SU(5)/SO(5) Georgi-Kaplan model, the minimal custodialpreserving SO(5)/SO(4) model and the minimal SU(3)/(SU(2)×U(1)) model, which intrinsically breaks custodial symmetry. We furthermore consider an extension of the Standard Model involving two new scalar particles around the TeV scale: a singlet neutral scalar φ, to be eventually identified as the Dark Matter candidate, plus a doubly charged SU(2)L singlet scalar, S++, that can be the source for the nonvanishing neutrino masses and mixings. Assuming an unbroken Z_2 symmetry in the scalar sector, under which only the additional neutral scalar φ is odd, we write the most general (renormalizable) scalar potential. This model may be regarded as a possible extension of the conventional Higgs portal Dark Matter scenario which in addition accounts for neutrino masses and mixings. This framework cannot completely explain the observed positron excess. However a softening of the discrepancy observed in conventional Higgs portal framework can be obtained, especially when the scale of new physics responsible, for generating neutrino masses and lepton number violating processes, is around 2 TeV.
Questa tesi si occupa di studiare modelli di Higgs Composto (HC), materia oscura e masse dei neutrini. In modelli di tipo HC, lo scalare di Higgs è uno pseudo-bosone di Goldstone associato che origina dalla rottura di una simmetria forte ad alta energia. Nella tesi costruiamo la Lagrangiana chirale bosonica effettiva, per un generico coset simmetrico G/H, derivando esplicitamente tutti gli operatori (sia CP-even che CP-odd) che appaiono fino a quattro derivate. Supponendo che l’uniche fonte di rottura di simmetria custodial siano quelle già presente nel Modello Standard (MS), studiamo la proiezione di questa Lagrangiana sulla Lagrangiana chirale di bassa energia del MS. Particolareggiamo questo studio considerando tre scenari particolari: il modello originale di Georgi-Kaplan SU(5)/SO(5), il modello minimale con simmetria custodial, SO(5)/SO(4), ed il modello minimale senza simmetria custodial, SU(3)/(SU(2) × U(1)). Nella tesi consideriamo inoltre unestensione del MS che coinvolge due nuove particelle scalari con massa alla scala TeV: un singoletto scalare neutro φ, che sarà poi identificato come candidato di materia oscura e un singoletto di SU(2)L scalare con carica q = 2, S++, che può essere la fonte per le masse e del mixing dei neutrini. Supponendo l’esistenza di una simmetria Z_2 nel settore scalare, sotto la quale solo φ è dispari, scriviamo il potenziale scalare (rinormalizzabile) più generale possibile. Il modello si può vedere come una possible estensione dei modelli con Higgs Portal in cui si tiene anche conto del meccanismo con cui generare le masse e i mixings dei neutrini. Il modello da noi studiato, pur predice un eccesso di positroni, non tale tuttavia da poter spiegare l’eccesso di positroni sperimentalmente osservato. Pur tuttavia si possono ottenere dei limiti meno stringenti rispetto ai normali modelli di Higgs Portal, in particolare se la scala della nuova fisica, responsabile della generazione delle masse dei neutrini e dei processi che violano il numero leptonico, è intorno ai 2 TeV.

This thesis is divided in two parts: the first part is dedicated to the study of black hole solutions in a theory of modified gravity, called massive gravity, that may be able to explain the actual stage of accelerated expansion of the Universe, while in the second part we focus on constraining primordial black holes as dark matter candidates.

In particular, during the first part we study the thermodynamical properties of specific black hole solutions in massive gravity. We conclude that such black hole solutions do not follow the second and third of law of thermodynamics, which may signal a problem in the model. For instance, a naked singularity may be created as a result of the evolution of a singularity-free state.

In the second part, we constrain primordial black holes as dark matter candidates. To do that, we consider the effect of primordial black holes when they interact with compact objects, such as neutron stars and white dwarfs. The idea is as follows: if a primordial black hole is captured by a compact object, then the accretion of the neutron star or white dwarf’s material into the hole is so fast that the black hole destroys the star in a very short time. Therefore, observations of long-lived compact objects impose constraints on the fraction of primordial black holes. Considering both direct capture and capture through star formation of primordial black holes by compact objects, we are able to rule out primordial black holes as the main component of dark matter under certain assumptions that are discussed.

To better understand the relevance of these subjects in modern cosmology, we begin the thesis by introducing the standard model of cosmology and its problems. We give particular emphasis to modifications of gravity, such as massive gravity, and black holes in our discussion of the dark sector of the Universe./

Cette thèse est divisée en deux parties :la première partie est consacrée à l’étude de certaines solutions de trous noirs dans une théorie modifiée de la gravité, appelée la gravité massive, qui peut être en mesure d’expliquer l’expansion accélérée de l’Univers; tandis que dans la seconde partie, nous nous concentrons sur des contraintes sur les trous noirs primordiaux comme candidats de matière noire.

En particulier, au cours de la première partie, nous étudions les propriétés thermodynamiques de solutions spécifiques de trous noirs en gravité massive. Nous en concluons que ces solutions de trous noirs ne suivent ni la deuxième, ni la troisième loi de la thermodynamique, ce qui semble indiquer une inconsistance dans le modèle. Par exemple, une singularité nue peut être créée à la suite de l’évolution d’un état sans aucune singularité.

Dans la deuxième partie, nous mettons des contraintes sur les trous noirs primordiaux en tant que candidats de matière noire. Pour ce faire, nous considérons l’effet des trous noirs primordiaux lorsqu’ils interagissent avec des objets compacts, tels que les étoiles à neutrons et les naines blanches. L’idée est comme suit :si un trou noir primordial est capturé par un objet compact, alors l’accrétion du matériel constituant l’étoile à neutrons ou la naine blanche est si rapide que le trou noir détruit l’étoile en un temps très court. Par conséquent, les observations d’objets compacts imposent des contraintes sur la fraction de trous noirs primordiaux. Considérant à la fois la capture directe des trous noirs primordiaux par les objets compacts et la capture au travers de la formation stellaire, nous sommes en mesure d’exclure les trous noirs primordiaux comme la composante principale de matière noire sous certaines hypothèses qui sont discutées.

Pour mieux comprendre la pertinence de ces sujets dans la cosmologie moderne, nous commençons la thèse par l’introduction du modèle standard de la cosmologie et de ses problèmes. Nous donnons une importance particulière aux modifications de la gravité, telles que la gravité massive, et aux trous noirs dans notre discussion sur le secteur sombre de l’Univers.
Doctorat en Sciences
info:eu-repo/semantics/nonPublished

In dieser Arbeit wird mit Hilfe von Daten, die mit dem High Energy Stereocopic System (H.E.S.S.) in Namibia aufgenommen wurden, indirekt nach dunkler Materie im Halo der Milchstraße gesucht
An indirect search for the presence of dark matter particles in the halo of the Milky Way with data that were recorded with the High Energy Stereoscopic System (H.E.S.S.) is discussed in this work

The modern era of particle physics is driven by experimental anomalies. Experimental efforts have become increasingly diverse and are producing enormous volumes of data. In such a highly data-driven scientific environment theoretical models are necessary to understand this data and to help inform the development of new experimental approaches. In this dissertation I present two significant contributions to this effort relevant to the energy, intensity, and cosmic frontiers of modern particle physics research. Part 1 of this dissertation discusses methods to understand modern dark matter direct detection results. In particular I present an analysis under the hypothesis of inelastic dark matter, which supposes that dark matter must scatter inelastically, i.e. that it must gain or loose mass during a collision with atomic nuclei. This hypothesis is attractive because it can alleviate otherwise contradictory results from a number of dark matter detection facilities. The main conclusion of this work is a presentation of the analytical tools, along with a mathematica package that can be used to run the analysis, and the discovery that there are regions of inelastic dark matter parameter space which are consistent with all current experimental results, and constraints. Part 2 of this dissertation discusses a phenomenon of modern interest called kinetic mixing which allows particles from the standard model to spontaneously transform into particles which experience a new, as of yet undiscovered, force. This phenomenon is relatively common and well motivated theoretically and has motivated significant experimental effort. In this work, I present an analysis of a general case of kinetic mixing, called nonabelian kinetic mixing. This work shows that, In general, kinetic mixing predicts the existence of a new particle and that, under certain conditions, this particle could be detected at modern particle colliders. Furthermore, the mass of this particle is related to the strength of kinetic mixing. This relationship suggests novel ways to constrain kinetic mixing parameter space, and if observed would provide a very striking indication that such a model is realized in nature.

It is the goal of this dissertation to demonstrate that beyond the standard model, certain theories exist which solve conflicts between observation and theory -- conflicts such as massive neutrinos, dark matter, unstable Higgs vacuum, and recent Planck observations of excess relativistic degrees of freedom in the early universe. Theories explored include a D-brane inspired construct of U(3) × Sp(1) × U(1) × U(1) extension of the standard model, in which we demonstrate several possible observables that may be detected at the LHC, and an ability to stabilize the Higgs mechanism. The extended model can also explain recent Planck data which, when added to HST data gives an excess of relativistic degrees of freedom of Δ N = 0.574 ± 0.25 above the standard result. Also explored is a possible non-thermal dark matter model for explanation of this result. Recent observations of Fermi bubble results indicate a signal of a 50 GeV dark matter particle annihilating into b b-bar, with a thermally averaged annihilation cross section corresponding to <σ v> = 8 × 10

(-27) cm

3/s, spurs interestin a Higgs portal model suggested by Steven Weinberg. Other implications of this model are also explored such as its ability to explain dark matter direct detection results along with LHC Higgs data, and Planck data. Particle physics is complimented by possible stochastic gravitational wave searches for which a model of second order global phase transitions is explored. These transitions generate gravitational wave spectra with amplitudes of order Ω(gw) h

2 = 10

(-24) - 10

(-15). Furthermore, techniques into such calculationsare investigated in hopes to improve the stability required in such lattice simulations.

The nature of dark matter and dark energy are currently two of the most important questions in cosmology. In this thesis, we consider studying the dark universe with the redshifts and peculiar velocities of galaxies. In the first half of the thesis, we analyse current peculiar velocity measurements of the bulk flow of our local volume to estimate the underlying dark matter power spectrum. In the second half of the thesis, we consider the prospects for measuring dark matter and dark energy with future galaxy redshift surveys, particularly via redshift space distortions. Fundamentally, bulk flow measurements and redshift space distortions are both sensitive probes of the power spectrum and growth rate of cosmic structure. In the final chapter, we directly compare power spectrum measurements with both methods.