Hybrid models of inflation are particularly interesting and well motivated, since easily embedded in various high energy frameworks like supersymmetry/supergravity, Grand Unified Theories or extra-dimensional theories. If the original hybrid model is often considered as disfavored, because it generically predicts a blue spectrum of scalar perturbations, realistic hybrid models can be in agreement with CMB observations. The dynamics of hybrid models is usually approximated by the evolution of a scalar field slowly rolling along a nearly flat valley. Inflation ends with a waterfall phase, due to a tachyonic instability. This final phase is usually assumed to be nearly instantaneous. <p> <p>In this thesis, we go beyond these approximations and analyze the exact 2-field non-linear dynamics of hybrid models. Several non trivial effects are put in evidence: 1) the possible violation of the slow-roll conditions along the valley induce the non existence of inflation at small field values. Provided super-planckian fields, the scalar spectrum of the original model is red, in agreement with CMB observations, independently of the position of the critical instability point. 2) Contrary to what was thought, the initial field values leading to inflation are not fine-tuned along the valley but also occupy a considerable part of the field space exterior to it. They form a complex connected structure with fractal boundaries that is the basin of attraction of the valley. Using bayesian methods, their distribution in the whole parameter space, including initial velocities, is studied. Natural bounds on the potential parameters are derived. 3) For the original model, after the field evolution along the valley, inflation continues for more than 60 e-folds along the waterfall trajectories in some part of the parameter space. Observable predictions are modified, and the scalar power spectrum of adiabatic perturbations is generically red, possibly in agreement with CMB observations. Moreover, topological defects are conveniently stretched outside the observable Universe. 4) The analysis of the initial conditions is extended to the case of a closed Universe, in which the initial singularity is replaced by a classical bounce. Contrary to some other scenarios, due to the attractor nature of the valley, the field values in the contracting phase do not need to be extremely fine-tuned to generate a bounce followed by a phase of hybrid inflation. <p> <p>In the third part of the thesis, we study how the present CMB constraints on the cosmological parameters could be ameliorated with the observation of the 21cm cosmic background from the dark ages and the reionization, by the future generation of giant radio-telescope. Assuming ideal foreground removals, forecasts on the cosmological parameters are determined for a characteristic Fast Fourier Transform Telescope experiment, by using both Fisher matrix and MCMC methods. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

Orientador: Saulo Henrique Pereira / Resumo: Efeitos térmicos em teoria de campos são estudados pela chamada Teoria de Campos a Temperatura Finita. Nessa dissertação estudamos os efeitos de temperatura de um campo fermiônico de dimensão de massa um (MDO), que obedece à equação Klein-Gordon em vez da de Dirac. A função de partição foi obtida por meio do formalismo de tempo imaginário e o resultado foi o mesmo que o obtido para campos fermiônicos padrões de Dirac. Obtemos os limites de alta e baixa temperatura, sendo que o limite de baixas temperaturas é proposto como sendo o responsável por manter os halos de matéria escura da galáxia numa região da mesma ordem ou maior que o raio galáctico. Para uma partícula leve com massa de 1eV e densidade de 0.1 partículas por cm³, o valor da massa total da matéria escura devido a partículas MDO é da mesma ordem da massa de uma galáxia típica. Tal resultado pode explicar a matéria escura como sendo formada por partículas fermiônicas de dimensão de massa um. Por fim, comparamos as estimativas de densidade dessas partículas com densidades obtidas através de dados de simulações numéricas e concluímos que para valores de massa entre 0.1eV a 1eV, as partículas MDO produzem uma massa típica de galáxias desde que a densidade delas esteja no intervalo de 10^(-2) cm^(-3) a 10^(5)cm^(-3). / Abstract: Thermal effects in feld theory are studied by the so called Finite Temperature Field Theory. In this dissertation we study the effects of temperature of a mass dimension one (MDO) fermionic field, which obeys the Klein-Gordon equation rather than the Dirac equation. The partition function was obtained via the imaginary time formalism and the result was the same as for the a Dirac fermionic field. We obtained the high and low temperature limits, and the latter is proposed as being responsable for keeping the dark matter halos of galaxies in a region greater than or of the same order as a typical galaxy radius. For a light particle of about 1eV and density of 0.1 particles per cm3 , the value of the total dark mass due to MDO particles is of the same order of a typical galaxy. Such result can explain dark matter as being formed by fermionic particles. Lastly, we compared those particles densities estimates with the ones obtained numeric simulation data and conclude that for mass values between 0.1eV and 1eV, the MDO particles yield a typical galaxy mass as long as their density is in the 10−2 cm−3 to 105 cm−3 interval / Mestre

In Chapter 1, we give an introduction to the topic of open string field theory. The concepts presented include gauge invariance, tachyon condensation, as well as the star product.<p>In Chapter 2, we give a brief review of vacuum string field theory (VSFT), an approach to open string field theory around the stable vacuum of the tachyon. We discuss the sliver state explaining its role as projector in the space of half-string basis. We review the construction of D-brane solutions in vacuum string field theory. We show that in the sliver basis the star product correspond to a matrix product. <p>Using the material introduced in the previous chapters, in Chapter 3 we establish a translation dictionary between open and closed strings, starting from open string field theory. Under this correspondence, we show that (off--shell) level--matched closed string states are represented by star algebra projectors in open string field theory. As an outcome of our identification, we show that boundary states, which in closed string theory represent D-branes, correspond to the identity string field in the open string side. <p>We then turn to noncommutative field theories. In Chapter 4, we introduce the framework in which we will work. The tools introduced are solitons, projectors, and partial isometries.<p>The ideas of Chapter 4 are applied to specific examples in Chapter 5, where we present new solutions of noncommutative gauge theories in which coincident vortices expand into circular shells. As the theories are noncommutative, the naive definition of the locations of the vortices and shells is gauge-dependent, and so we define and calculate the profiles of these solutions using the gauge-invariant noncommutative Wilson lines introduced by Gross and Nekrasov. We find that charge 2 vortex solutions are characterized by two positions and a single nonnegative real number, which we demonstrate is the radius of the shell. We find that the radius is identically zero in all 2-dimensional solutions. If one considers solutions that depend on an additional commutative direction, then there are time-dependent solutions in which the radius oscillates, resembling a braneworld description of a cyclic universe. There are also smooth BIon-like space-dependent solutions in which the shell expands to infinity, describing a vortex ending on a domain wall.<p>In Chapter 6, we review the Fronsdal models for free high-spin fields that exhibit peculiar properties. We discuss the triplet structure of totally symmetric tensors of the free String Field Theory and their generalization to AdS background.<p>In Chapter 7, in the context of massless higher spin gauge fields in constant curvature spaces discussed in chapter 6, we compute the surface charges which generalize the electric charge for spin one, the color charges in Yang-Mills theories and the energy-momentum and the angular momentum for asymptotically flat gravitational fields. We show that there is a one-to-one map from surface charges onto divergence free Killing tensors. These Killing tensors are computed by relating them to a cohomology group of the first quantized BRST model underlying the Fronsdal action.<p><p> / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

Cette thèse intitulée « Studies of fractional D-branes in the gauge/gravity correspondence & Flavored Chern-Simons quivers for M2-branes » se place dans le cadre de la théorie des cordes, en physique théorique. Elle consiste en une introduction suivie de deux parties. Dans l'introduction sont résumés les différents outils de théorie des cordes qui seront utilisés. <p>\ / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

In this thesis, we study certain non-perturbative aspects of N=1 gauge theories. We show how to compute the expectation values of chiral operators (i.e. those that preserve the anti-chiral supercharges) exactly from a first-principle approach based on the path integral over the microscopic fields. <p><p>The text is divided into two parts. The first one consists of an original introduction to the tools that underlie the researches and results obtained during this thesis. After a general introduction, we present some methods to obtain exact results. Covered topics include instantons, N=2 supersymmetry and localization,N=1 supersymmetry and holomorphy, and finally the Dijgraaf-Vafa matrix model formalism and the perturbative generalized Konishi anomaly equations. These preliminaries were chosen to enlighten the presentation of our results. A brief overview of our results is then. This includes localization in some N=1 gauge theories, its applications to the computation of chiral correlators as well as a non-perturbative discussion of the generalized Konishi equations and of the Dijkgraaf-Vafa glueball superpotential. We insist on the ideas and the results, postponing the details for the second part, which consists of a faithful reproduction of the papers published during this thesis and in which the author has been involved. /<p><p>Dans cette thèse, nous étudions certains aspects non-perturbatifs des théories de jauge supersymétriques N=1. Plus précisemment, nous montrons comment les valeurs moyennes des opérateurs chiraux (qui préservent la moitié des supercharges) dans les vides quantiques peuvent être calculées sans approximations, à partir d'une approche basée sur l'intégrale fonctionnelle sur les champs microscopiques. <p><p>Ce mémoire est divisé en deux parties. La première consiste en une introduction à l'approche microscopique des théories de jauge supersymétriques. Une grande fraction de celle-ci est dédiée à la présentation des concepts et méthodes qui sont à la base du développement de ce formalisme et de nos recherches. Ceci inclut les instantons, la supersymétrie N=2 et la localisation dans l'intégrale fonctionnelle, la supersymétrie N=1 et l'holomorphie, et enfin l'approche de Dijkgraaf-Vafa basée sur un modèle de matrices et les équations d'anomalie généralisées de Konishi. Ensuite, nous présentons le formalisme microscopique et les résultats obtenus durant cette thèse. Nous expliquons comment utiliser la technique de localisation dans certaines théories de jauge N=1 et comment l'appliquer au calcul des valeurs moyennes des opérateurs chiraux. Nous discutons également de façon non-perturbative les équations d'anomalie généralisées de Konishi et le superpotentiel de Dijkgraaf-Vafa. La plupart des résultats exacts connus dans les théories de jauge N=1 sont reproduits, dont la condensation des gluinos et la brisure de la symétrie chirale.<p>Nous insistons sur les idées et les résultats plutôt que sur les détails techniques. Ceux-ci sont décrits dans la seconde partie de ce mémoire, qui consiste en une reproduction fidèle des travaux publiés durant cette thèse. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished