Recentes observações astrofísicas, em especial de supernovas tipo Ia e das anisotropias da radiação cósmica de fundo, indicam que recentemente na história do universo um tipo desconhecido de energia passou a dominar sua evolução induzindo uma expansão acelerada. Esta componente misteriosa ficou conhecida como energia escura. Nosso objetivo é o estudo da energia escura, através de modelos com constante cosmológica, campo escalar canônico e com o campo de Born-Infeld. Para os modelos com campo escalar, usando potenciais tipo lei de potência, estudamos soluções atratoras para a evolução homogênea. Também estudamos, na aproximação de largas escalas, soluções atratoras para as perturbações dos campos escalares. Mostramos que, para modelos de energia escura com campo escalar canônico, as soluções atratoras a nível perturbativo não geram modos de isocurvatura. Para o campo de Born-Infeld, fazemos uma análise de estabilidade de suas soluções atratoras a nível perturbativo, determinamos em que circunstâncias elas podem gerar modos de isocurvatura. Para os modelos de energia escura mais realistas, estes modos tendem a ser pequenos. / Recent astrophysical observations, specially supernova type Ia and cosmic microwave back­ ground anisotropies, indicate that recently in the history of the universe, some unknown type of energy is dominating its evolution and inducing an accelerated expansion. This mysterious component has been named dark energy. Our aim is to study dark energy, by using cosmological constant, canonical scalar field and Born-Infeld scalar field models. In the models with scalar field, using power law potentials, we study attractor solutions for the homogeneous evolution. We also study, in the large scale approximation, attractor solutions for the scalar field perturbations. We show that, for models with canonical sca­ lar field , the attractor solutions for its perturbations do not generate isocurvature modes. For the Born-Infeld scalar field, we analyze the stability of its attractor solutions in the perturbative levei, and we determine in which case they can generate isocurvature modes. For the more realistic dark energy models, these modes tend to be small.

Consideramos uma teoria escalar acoplada não minimamente à gravitação no contexto de alguns modelos inflacionários. Mostramos como esse acoplamento inviabiliza a inflação caótica. Analisamos em seguida um modelo proposto por Linde para contornar esses problemas. Mostramos que sua realização é trivial. / We consider a scalar theory non minimally coupled to gravitation in the context of some inflationary models. We show how this coupling prevents the chaotic inflation. Then analyzed a model proposed by Linde to avoid these problems. We show that its realization is trivial.

Esta tese consiste na etnografia dos Deni do rio Cuniuá, localizados no sudoeste do estado do Amazonas e falantes de uma língua da família linguística arawá. Esta parte da população Deni vive em um relativo isolamento frente à sociedade brasileira, num cenário que contrasta com o intenso contato que mantinham algumas décadas atrás. A situação atual é antes o resultado de fatores histórico, como a crise do extrativismo e a demarcação das Terras Indígenas na região, do que do desejo dos próprios indígenas. A abordagem adotada coloca em primeiro plano o parentesco Deni, tomado como fio condutor e não como limite da análise. Abordando algumas temáticas da cosmologia deni, como a questão dos brancos, dos coletivos, da relação com os animais, da noção de pessoa, do casamento e dos vínculos de filiação, mostramos como o parentesco, longe de ser um domínio isolado, está relacionado com vários outros elementos do mundo. Realizamos aqui um exercício baseado em uma metodologia experimental para o estudo de genealogias, demonstrando como alguns aspectos do cosmos Deni influenciam suas práticas matrimoniais. / This thesis is an ethnographic account of the Deni people, who live on the River Cuniuá at the Southwest corner of the Amazonas State and speak a language that belongs to the arawan family. This part of the Deni population currently lives in relative isolation from Brazilian society, which contrasts with the intense contacts of a few decades ago. The current situation is a direct result of historical factors such as the crisis of the extraction industry and the demarcation of native-land, and not the Denis own desire. The approach adopted by the present work focuses on, but is not limited by, Deni kinship. It addresses some elements of Deni cosmology, such as their relations with the whites, the nominated groups, the animals, as well as their conception of personhood, marriage and filiation, and demonstrates the manner in which kinship relates to several other elements of the their world. The present work conducts an exercise based on an experimental methodology for studies of genealogy, thus demonstrating how some aspects of the Deni cosmos play an influence on their marriage practices.

Thesis (M.Div.)--Chinese University of Hong Kong. / Bibliography: leaves 125-136.

iPTF15dtg is a supernova (SN) Type Ic (lacking hydrogen and helium in its spectrum) with a light curve indicating that it is the result of a massive star explosion. Taddia et al. (2016) suggested that the progenitor star was a Wolf-Rayet (WR) star that previously suffered strong mass loss. More recent observations show that the SN light curve did not decline as expected, indicating the existence of an additional power source. One possibility is a magnetar, a hyper-magnetic neutron star capable of injecting its rotational energy into the light curve during relevant time scales. This bachelor thesis adds previously unpublished data to the iPTF15dtg light curve and compares simple semi-analytical models to rule out a radioactive scenario and discuss the possibility of a magnetar as the primary source of luminosity.

Globular Clusters contain very old metal-poor stars in different evolutionary stages evolved from the same primordial cloud. Signatures of atomic in stellar interiors are studied in the metal-poor GC M30. Furthermore, traces of cluster internal pollution depleting alpha elements e.g. Mg & O are also found through high precision spectroscopy, which favors the existence of multiple stellar populations within a Globular Cluster. In this work, I use spectroscopic observations of 177 sample stars using the multi object spectrograph GIRAFFE and increasing the initial size of 12 of Scheutwinkel (2018) by 13 new UVES spectrograph sample stars of the Globular Cluster M30 ([Fe/H] = -2.3). The abundances of Fe, Ti, Mg & Ba (GIRAFFE) and Fe, Na, Al & Mg (UVES) are derived through the graphical spectrum analysis program SIU with VI broadband photometric stellar input parameters. The underlying line-formation theory is in LTE and uses 1-dimensional hydrostatic plan-parallel MAFAGS atmospheres with mixing length convection. We confirm an Al-Mg anti-correlation (Spearman ϱs= -0.583) and a correlation (Spearman ϱs= 0.641) between Al-Na in RGB stars as a direct result of being the partner elements of the depleted alpha elements Mg & O caused through NeNa, ON and MgAl cycles. We find similar element ratios [X/Fe] as Carretta et al. (2018) & O‘Malley et al. (2018) favoring the prior existence of multiple stellar populations within M30. Furthermore, we detected a signifcant restoration of abundances in the elements Fe, Mg & Ba towards RGB stars. Fe, Mg and Ti are matching the predictions of the diffusion model T5.8 (Richard et al. 2005) reasonably well. For Ba, we have no current atomic diffusion modeling, so the validation of the results is not possible. The trend of Ti is v-shaped presumably due to stronger radiative accelaration effects for this element. Overall our relative abundance trends are consistent with other Globular Cluster studies by Gruyters et al. (2013&2016), Korn et al. (2007) & Lind (2007).

The halos of galaxies - consisting of gas, stars, and satellite galaxies - are formed and shaped by the most fundamental processes: hierarchical merging and the flow of gas into and out of galaxies. While these processes are hard to disentangle, metals are tied to the gas that fuels star formation and entrained in the wind that the deaths of these stars generate. As such, they can act as important indicators of the star formation, the chemical enrichment, and the outflow histories of galaxies. Thus, this thesis aims to take advantage of such metal signatures in the stars and gas to place observational constraints on current theories of galaxy evolution as implemented in cosmological simulations. The first two chapters consider the metallicities of stars in the stellar halo of the Milky Way and its surviving satellite dwarf galaxies. Chapter 2 pairs an N-body simulation with a semi-analytic model for supernova-driven winds to examine the early environment of a Milky Way-like galaxy. At z=10, progenitors of surviving z=0 satellite galaxies are found to sit preferentially on the outskirts of progenitor halos of the eventual main halo. The consequence of these positions is that main halo progenitors are found to more effectively cross-pollute each other than satellite progenitors. Thus, inhomogeneous cross-pollution as a result of different high-z spatial locations of different progenitors can help to explain observed differences in abundance patterns measured today. Chapter 3 expands this work into the analysis of a cosmological, hydrodynamical simulation of dwarf galaxies in the early universe. We find that simple assumptions for modeling the extent of supernova-driven winds used in Chapter 2 agree well with the simulation whereas the presence of inhomogeneous mixing in the simulation has a large effect on the stellar metallicities. Furthermore, the star-forming halos show both bursty and continuous SFHs, two scenarios proposed by stellar metallicity data. However, the metallicity distribution functions of the simulated halos are both too metal rich and too peaked when compared to the data. This comparison reveals that a complex SFH and a broad metallicity distribution can develop rapidly in the early Universe. The third chapter moves to the present day with a consideration of the circumgalactic medium (CGM) around nearby Milky Way-like galaxies. We compare a cosmological simulation of a Milky Way-like galaxy to recent absorption line data and find that a reduced extragalactic ultraviolet background brings the column density predictions into better agreement with the data. Similarly, when the observationally derived physical properties of the gas are compared to the simulation, we find that the simulation gas is always at temperatures approximately 0.5 dex higher. Thus, similar column densities can be produced from fundamentally different gas. Metal-line emission is then considered as a complementary approach to studying the CGM. From the simulations, we find that the brightest emission is less sensitive to the extragalactic background and that it closely follows the fundamental filamentary structure of the halo. This becomes increasingly true as the galaxy evolves from z = 1 to z = 0 and the majority of the gas transitions to a hotter, more diffuse phase. Finally, resolution is a limiting factor for the conclusions we can draw from emission observations but with moderate resolution and reasonable detection limits, upcoming instrumentation should place constraints on the physical properties of the CGM. Future work advancing the techniques in this thesis remain promising for putting new observational constraints on our theories of galaxy evolution.

No presente trabalho, revisamos o bem estabelecido formalismo de formação de estruturas no universo e a fundamentação teórica do espectro de potência da matéria Revisamos então a literatura atual sobre estimação do espectro de potência, focando nos mêtodos de análise de Fourier que possuem conexão com o formalismo da matriz de Fisher. Com a mesma motivação, desenvolvemos um conjunto de estimadores para levantamentos de galáxias com múltiplas espécies e testamos eficientemente nossas previsões em catálogos artificias simplificados. Esse método é adequado parar tratar levantamentos contendo diferentes espécies de traçadores da estrutura em larga escala, como galáxias, quasares, sistemas de absorção de Lyman-alfa, etc. Encontramos boa concordância entre nossas expectativas e os resultados numéricos, e uma notável superioridade do nosso método quando comparado a outros pré-existentes. / In the present work, we review the well established formalism of structure formation in the universe and the theoretical foundation for the matter power spectrum. We then review the current literature on power spectrum estimation, focusing on Fourier methods that have a close connection to the Fisher matrix formalism. With the same motivation, we develop a set of estimators for surveys with multiple galaxy species and efficiently test our predictions in simple mock catalogs. This method is suitable for treating surveys containing different species of tracers of large-scale structure, such as galaxies, quasars, Lyman-alpha absorption systems, etc. We find good agreement between our expectations and the numerical results, and a remarkable superiority of our method when compared to pre-existing ones.

In the present monograph we study in detail the primordial gravitational waves in cosmologies with a decaying vacuum. The decaying vacuum models are an alternative to solve the cosmological constant problem attributing a dynamic to the vacuum energy. The problem of primordial gravitational waves is discussed in the framework of an expanding, flat, spatially homogeneous and isotropic FLRW Universe described by General Relativity theory with decaying vacuum energy density of the type $\\Lambda \\equiv \\Lambda(H)$. Two particular interesting limits of a class of decaying vacuum models were investigated. A first-order tensor perturbation term was introduced to the FLRW metric, the evolution equation of the perturbations was derived and then expressed in terms of a Fourier expansion, the time-dependent part decouples from the spatial part. The resulting equation has the form of a damped harmonic oscillator which depends on the scale factor, which carries all the cosmological and decaying vacuum characteristics. In the first model studied, the decaying vacuum has the form $\\Lambda \\propto H^2$. The gravitational wave equation is established and its time-dependent part has analytically been solved for different epochs in the case of a flat geometry. The main result is unlike the standard $\\Lambda$CDM cosmology (no interacting vacuum): in this model there is gravitational wave amplification during the radiation era, which in quantum field theory means graviton production. This difference is a clear signature of the decaying vacuum models which a eventual observation could give empirical clues about it. However, high frequency modes are damped out even faster than in the standard cosmology, both in the radiation and matter-vacuum dominated epoch. The physical gravitational wave quantities like the modulus of the mode function, power and gravitational wave energy density spectra generated at different cosmological eras are also explicitly evaluated. The second model studied is a decaying vacuum of the form $\\Lambda \\propto H^3$. This model drives a nonsingular flat cosmology which is termed complete in the sense that the cosmic evolution occurs between two extreme de Sitter stages. The particularity which makes interesting this model is that the transition from the early de Sitter era to the radiation phase is smooth avoiding the graceful exit problem. The gravitational wave equation is derived and its time-dependent part numerically integrated in a relevant period previously delimited. The gravitational wave solutions for the other eras were calculates analytically. Today\'s gravitational wave spectra were calculated and compared with the standard result where an abrupt transition is assumed. It is found that the stochastic background of gravitational waves is very similar to the one predicted by the cosmic concordance model plus inflation except for the higher frequencies. / Na presente monografia foi estudado em detalhe as ondas gravitacionais primordiais em cosmologias com decaimento do vácuo. Os modelos de decaimento do vácuo são uma alternativa para resolver o problema da constante cosmológica atribuindo uma dinâmica à energia do vácuo. O problema de ondas gravitacionais primordiais é discutida no âmbito de um Universo FLRW em expansão, plano, espacialmente homogêneo e isotrópico descrito pela teoria da Relatividade Geral com decaimento da densidade de energia do vácuo do tipo $\\Lambda \\equiv \\Lambda(H)$. Dois limites particularmente interessantes de uma classe de modelos de decaimento do vácuo foram trabalhados. Um termo tensorial perturbativo a primeira ordem foi introduzido na métrica de FLRW, a equação de evolução das perturbações foi derivada e depois expressada em termos de uma expansão de Fourier, a parte dependente do tempo desacopla-se da parte espacial. A equação resultante tem a forma de um oscilador harmônico amortecido que depende do fator de escala que carrega todas as características cosmológicos e do decaimento do vácuo. No primeiro modelo estudado, o decaimento do vácuo tem a forma $\\Lambda \\propto H^2$. A equação da onda gravitacional é estabelecida e a sua parte dependente do tempo foi resolvida analiticamente para diferentes épocas no caso de uma geometria plana. O resultado principal é que a diferença da cosmologia $\\Lambda$CDM padrão (sem decaimento do vácuo), neste modelo ocorre amplificação de ondas gravitacionais durante a era de radiação, que em mecânica quântica significa produção gráviton. Esta diferença é uma assinatura clara dos modelos de decaimento do vácuo que uma eventual observação poderia dar pistas empíricas sobre o assunto. No entanto, os modos de alta frequência são amortecidos ainda mais rápido do que na cosmologia padrão, tanto na era da radiação e da matéria-vácuo. As quantidades físicas das ondas gravitacionais, como o módulo da função de modos, espectros de potência e de densidade de energia de onda gravitacional geradas em diferentes eras cosmológicas também foram avaliadas explicitamente. O segundo modelo estudado é um decaimento do vácuo da forma $\\Lambda \\propto H^3$. Este modelo leva uma cosmologia plana não singular que é denominado completo no sentido de que a evolução cósmica ocorre entre duas eras de Sitter extremas. A particularidade que torna interessante este modelo é que a transição do início da era de Sitter era para a fase da radiação é suave evitando o graceful exit problem. A equação gravitacional é derivada e sua parte dependente do tempo foi integrada numericamente num período relevante previamente delimitado, as soluções das ondas gravitacionais para as outras eras foram calculadas analiticamente. Os espectros de hoje das ondas gravitacionais foram calculados e comparados com os cálculos padrão onde é assumida uma transição abrupta. Verificou-se que o fundo estocástico de ondas gravitacionais é muito semelhante ao previsto pelo modelo de concordância cósmica mais a inflação, exceto para as frequências mais altas.

Cosmic microwave background observations have been fundamental in forming the standard model of cosmology. Ongoing and upcoming cosmic microwave background experiments aim to confirm this model and push the boundaries of our knowledge to the very first moments of the Universe. Non-cosmological microwave radiation from the Galaxy and beyond, called foregrounds, obscures and contaminates these measurements. Understanding the sources and effects of foregrounds and removing their imprint in cosmic microwave background observations is a major obstacle to making cosmological inferences. This thesis contains my work studying these foregrounds. First, I will present observations of a well-known but poorly understood foreground called anomalous microwave emission. Second, I will present results forecasting the capability of a next-generation satellite experiment to detect cosmic microwave background spectral distortions in the presence of foregrounds. Third, I will present results studying the effect of foregrounds on the cosmic microwave background self-calibration method, which allows experiments to calibrate the telescope polarization angle using the cosmic microwave background itself. Fourth, I will present my analysis characterizing the performance of and producing maps for the E and B Experiment. Fifth, I will present my research contributions to the readout system that used in the laboratory to operate kinetic inductance detectors, which are being developed for cosmic microwave background observations. Lastly, I will conclude with future prospects in the field of foregrounds and cosmic microwave background cosmology.