Três aplicações de campos escalares a cosmologias homogêneas e isotrópicas são apresenta- das, com motivações e resultados diversos. No primeiro caso, uma técnica de multiplicadores de Lagrange é usada para estabelecer vínculos físicos sobre os invariantes de curvatura possivelmente presentes na ação efetiva de baixas energias da teoria de cordas. Um modelo não-singular é obtido em um caso partícula, sugerindo uma possível correção na ação da gravitação compatível com as simetrias das cosmologias de cordas. Numa outra abordagem, é proposto um modelo fenomenológico não-singular baseado no decaimento do termo cosmológico. O modelo tem como principal característica uma passa- gem suave entre uma fase inflacionária do tipo de Sitter e uma fase com dinâmica do tipo Friedmann-Robertson-Walker. Como último exemplo é considerado um campo escalar acoplado termicamente ao fluido cósmico. Adotando um termo dissipativo específico, mas usual, é definido um espaço de parâmetros contendo as cosmologias com campos escalares mais comuns e o modelo padrão como casos particulares. As condições de rolamento lento são obtidas e é apresentado um modelo cosmológico simples para exemplificar o potencial heurístico dos parâmetros propostos. / Three applications of scalar fields to homogeneous and isotropic cosmologies are presented, with distinct motivations and resuIts. In the first case, a Lagrange multiplier technique is used in order to set physical constraints on the curvature invariants possibly present in the low energy effective action of string theory. In a particular case, a nonsingular model is obtained, suggesting a possible correction in the gra- vity action which is compatible to the symmetries of string cosmology. In another approach, a nonsingular model based on the decay of the cosmological term is pro- posed. The model has as a major feature a smooth transition between an inflationary de Sitter phase and a phase with FRW-type dynamics. As a last example, a scalar field thermally coupled to the cosmic fluid is considered. By adop- ting a specific but usual dissipative term, it is defined a parameter space encompassing the most common scalar field cosmologies, as well as the standard model, as limiting cases. Slow roll conditions are obtained and it is presented a simple toy model to illustrate the heuristic potential of the proposed parameters.

Standard models of cosmology use inflation as a mechanism to resolve the isotropy and homogeneity problem of the universe as well as the flatness problem. However, due to various well known problems with the inflationary paradigm, there has been an ongoing search for alternatives. Perhaps the most famous among these are the cyclic universe scenarios which incorporate bounces. As these scenarios have a contracting phase in the evolution of the universe, anisotropies and inhomogeneities would be expected to blow up on approach to the bounce. Thus, it is reasonable to ask whether the problems of homogeneity and isotropy can still be resolved in these scenarios. In this thesis, I will focus on the problem of the resolution of the isotropy problem. I begin with a brief review of anisotropic, spatially homogeneous geometries of cosmological interest. Next, I review the existing literature on bouncing cosmologies, and discuss the mechanism of bounce studied in previously proposed models, as well as their theoretical and observational advantages and disadvantages. I then discuss the process of isotropisation in the contracting phase of each bounce. In this phase of the evolution, the mechanism of ekpyrosis is used in most cosmological scenarios which incorporate a contracting phase to mitigate the problem of anisotropies blowing up on approaching the bounce. I start by studying anisotropic universes and I then examine the effect of the addition of ultra-stiff anisotropic pressures on the ekpyrotic phase. I then consider evolving such anisotropic universes through several cycles with increasing expansion maxima at each successive bounce. This eventually leads to flatness in the isotropic case. My aim is to see if the resolution of the flatness problem also leads to a simultaneous resolution of the isotropy problem. In the next chapter, I consider the effect of non comoving velocities on the shape of this anisotropic bouncing universe. In the final section of my thesis, I consider anisotropic cosmological models within the context of canonical quantum cosmology and investigate the quantum behaviour of anisotropies.

Cosmology is one of the best tools to understand the physics that governs the universe at high energies. On one hand, inflation is a very robust mechanism to explain the initial conditions of the universe. On the other hand general relativity provides a solid framework for the formation of cosmic structures at cosmological scales. Nevertheless, there are still important issues that remain without a clear answer. For example, inflation still lacks of a concrete microphysical description, and also there is still no satisfactory mechanism to explain the late time acceleration of the universe. This thesis addresses these two topics. In the first part we discuss the effects of heavy degrees of freedom coupled to inflation. This has been an important topic over the years, because the experimental success might make it possible to detect new degrees of freedom in inflation. In chapter two we discuss the case when non relativistic heavy fields are coupled to the inflaton through a non minimal gravitational coupling. Here we find that, for certain geometries, the heavy field can modify the potential for a few e-folds, either stopping inflation, or setting its initial conditions. In chapter 3 we study the dynamics of fluctuations in holographic inspired models of multi-field inflation. We find that the entropy mass $\mu$ (the mass of the fluctuation orthogonal to the trajectory of inflation) satisfies an universal upper bound given by $\mu \leq 3 H / 2$. This bound coincides with the requirement of unitarity of conformal operators living on the boundary of the theory. In the second part of the thesis we study high energy effects on the Cosmic Microwave Background (CMB). In the fourth chapter we study the role of disformal transformation on cosmological backgrounds and its relation to the speed of sound for tensor modes. A speed different from one for tensor modes can arise in several contexts such as Galileons theories, or massive gravity. Nevertheless the speed is very constrained to be one by observations of gravitational wave emission. It has been shown that in inflation a disformal transformation allows the speed for tensor modes, to be set to one without making changes to the curvature power spectrum. We show that on the CMB, after doing the transformation, there is an imprint on the acoustic peaks, and the diffusion damping. This has interesting consequences: for a particular class of theories the transformation can be used to constrain the parameter space in different regimes. In chapter five we study the impact of gravitons with non-vanishing masses on the polarisation of th CMB . We also focus on putative modifications to the speed of the gravitational waves. We find that a change of the graviton speed shifts the acoustic peaks of the B-mode polarization and then could be easily constrained. In all cases when both massless and massive gravitons are present, we find that the B-mode CMB spectrum is characterised by a low $l$ plateau together with a shifted position for the first few peaks compared to a massless graviton spectrum. This shift depends on the mixing between the gravitons in their coupling to matter and could serve as a hint in favour of the existence of multiple gravitons.

This dissertation presents an interdisciplinary research project studying Inka engagement with the heavily modified ritual landscape of the 3000 hectare Saqsawaman Archaeological Park, located just north of the former imperial capital of Cuzco. First, through a close reading of cosmogenesis narratives, and a careful application of ethnographic comparison, I examine the nature of actors and agency in Andean and Inka thought and practice. Specifically, I bring up five themes - vitality, communication, identity, complementarity, and positioning - that are prevalent in Andean cosmology and that were therefore capitalized on in the built landscapes of the Inka. While prior research has focused on Inka stonework, I argue that it is the combination of stone with other elements - most notably water and the subterranean - that allows the most symbolically powerful deployment of landscape in epistemology and cosmology. This argument is supported by an archaeological examination that uses survey and GIS techniques to map the Inka efforts at landscape manipulation in Saqsawaman. The results show that the Inka focused their efforts on areas where a combination of stone and water, along with subterranean access and viewsheds of sacred landscape, allowed for a more symbolically rich engagement with their universe. The ethnographic research and the survey together show that while stone was an important and enduring element in Andean belief systems, it is actually water which was the most important element of the ritual practice that sustained the cosmological universe. As a result, administrative focus on bounded stone sites has allowed elements such as water, as well as areas outside these boundaries, to be designated as unimportant - a process that has led to the loss of a great deal of knowledge and understanding grounded in a more comprehensive view of the larger landscape.

Apresentamos neste trabalho uma generalização da teoria de perturbações cosmológicas para o caso de universos homogêneos e anisotrópicos, caracterizados por um espaço-tempo do tipo Bianchi I. Como aplicação da teoria, investigamos as conseqüências de uma fase inflacionária e anisotrópica do universo dos pontos de vista clássico e quântico. Após uma discussão da evolução do espaço-tempo de fundo nós quantizamos os modos perturbativos para, em seguida, construir o espectro de potências das perturbações de curvatura e de ondas gravitacionais do fim da inflação. Nossos resultados mostram que as principais características de uma fase anisotrópica primordial do universo são: (1) dependência direcional dos espectros de potências, (2) acoplamento entre as perturbações de curvatura e as ondas gravitacionais e (3) espectros distintos para as diferentes polarizações das ondas gravitacionais em grandes escalas cosmológicas. Todos esses efeitos são importantes apenas em grandes escalas cosmológicas e, localmente, recuperamos a teoria isotrópica de perturbações cosmológicas. Nossos resultados dependem de uma escala característica que pode, embora não seja estritamente necessário, ser ajustada a alguma escala observável. / In this work we generalize the standard theory of cosmological perturbations to the case of homogeneous and anisotropic universes described by a Bianchi I spacetime metric. As an application of this theory we investigate the predictions of an inflationary anisotropic phase, both at the classical and quantum level. After discussing the evolution of the background spacetime, we solve and quantize the perturbation equations in order to predict the power spectra of the curvature perturbations and gravity waves at the end of inflation. Our results show that the main features of an early anisotropic phase are: (1) a dependence of the spectra on the direction of the modes, (2) a coupling between curvature perturbations and gravity waves, and (3) the fact that the two gravity waves polarisations do not share the same spectrum on large scales. All these effects are significant only on large scales and die out on small scales where isotropy is recovered. Finally, our results depend on a characteristic scale that can, but a priori does not have to, be tuned to some observable scale.

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In this thesis, I present my work related to the characterization of diffuse Galactic foregrounds for observing the polarization of the Cosmic Microwave Background (CMB) radiation, and the impact of these foregrounds on the measurement of cosmological parameters. One of the most important future challenges for cosmology is the potential detection of polarization B-modes of the CMB. Inflation is a theory that explains the extremely early Universe, and solves several problems that were present in classical cosmology. It describes the anisotropies observed in the current Universe as primordial quantum fluctuations stretched by rapid exponential expansion. A key prediction of inflation is the production of a background of primordial gravitational waves, which could be detected through the associated large-scale B-mode signal in the CMB polarization. The amplitude of the B-mode signal, which depends on the energy scale of inflation, is parametrized by the tensor-to-scalar ratio r. Diffuse emission from within our Galaxy, and other extra-Galactic sources, collectively referred to as CMB foregrounds, obscure a fraction of the cosmological signal from the CMB radiation. This is a huge problem, because they have to be cleaned using data analysis methods, called component separation. A significant challenge for the potential detection of the primordial B-mode signal is that it can be extremely small, to the extent that it can be dominated even by the residual foreground contamination after component separation. In this work, we characterize these foreground residuals and assess their impact on the cosmological parameters. We create a method to simulate observations of the microwave sky, including diffuse Galactic foregrounds, CMB realizations and instrumental noise. These simulations are used to propagate errors on the characterization of foregrounds through the analysis procedures employed in the observations of the CMB, including component separation, angular power spectra calculation and cosmological parameter estimation. We estimate the bias and the σ error for the tensor-to-scalar ratio, to quantify the impact of the foreground residuals in the cosmological signal. We also propose a novel method to model these residuals when determining cosmological parameters, in order to avoid a bias on the r parameter. We performed forecasts and optimization analyses for two proposed CMB polarization experiments: the Simon Observatory, a funded ground-based telescope that will observe the polarization of the CMB from the Atacama desert in Chile, and CORE, a proposed next-generation CMB satellite experiment. All of our work shows that the issue of foreground residuals must be considered very carefully in future studies. Foreground spectral parameters must be modelled very accurately, with errors < 0.5%, if we wish to measure a value r âˆ1⁄4 10^−3. These foreground residuals can easily be mistaken as primordial cosmological signals, so our work motivates further research into developing new data analysis techniques.

Weak gravitational lensing is now well established as a powerful cosmological probe, particularly for studying large scale structure growth in the Universe. The vast majority of weak lensing experiments to date use optical and near infrared observations which are well suited to the requirements in source densities and shape analysis. In this thesis we outline the prospects associated with weak lensing surveys from radio observations. This can offer key advantages to optical counterpart studies such as the well defined observing beam pattern of a radio telescope and a window into a much broader observed redshift distribution. In addition to the prospect of radio weak lensing surveys alone, combining with optical counterparts in a cross-correlation study has been shown to mitigate uncorrelated systematics, further motivating the case for radio based weak lensing studies. The correlation of galaxy shapes through multi-wavelength observations will affect the noise on the cosmological power spectrum in cross-correlation analysis. We use radio and optical observations of the COSMOS field with the VLA and HST respectively, accompanied with simulations for calibration in order to measure shape correlations between wavelength regimes. Although we do not detect a correlation between optical and radio shapes, a lower limit on the intrinsic astrophysical scatter was placed at >0.212pi (or 38.2 degrees), through a Monte Carlo simulation of source catalogues with the measured uncertainties. The SuperCLASS experiment aims to measure a weak lensing signal with radio observations from a super-cluster field. We introduce the radio data, collected with the e-MERLIN and JVLA, and the reduction steps taken. Assisted by simulations, we have designed a shape measurement pipeline (SuperTRAP) which performs additional phase rotation and averaging steps to extract visibility sets on a source by source basis followed by image plane shape analysis. A series of staged tests of increasing complexity are outlined here and evaluated by the shape recovery bias and efficiency. Finally we present the optical counterpart observations and shape analysis for the SuperCLASS field, with data collected by the Subaru Suprime-Cam. Observational systematics are measured to form representative PSF models in each CCD exposure and the subsequent shape analysis from the I band photometry is presented. Shear analysis from the measured power spectrum shows good agreement with theoretical predictions. From the measured shear power spectrum we detect a strong signal in the E-mode band powers, equivalent to a 9.31sigma detection. Our measurements from the B-mode and E-B cross band powers suggest negligible contamination from systematics. The optical analysis presented here will provide the counterpart analysis to the radio for future cross-correlation studies.

This thesis is a study of the influence of cosmology on Apollonius Rhodius’ Argonautica, an epic hexameter poem written in Alexandria in the 3rd century BC. I examine ancient Greek ideas of cosmogony and cosmology, which range from the earliest extant Greek texts (Homer and Hesiod) to contemporaries of Apollonius (Aratus). My argument is that cosmology is deeply embedded in the text, and that Apollonius creates a nexus of cosmic intertexts which provides a scientific and intellectual backdrop against which the events of the narrative take place. The narrative’s events all occur within a cosmos, which is alluded to throughout the epic; the reader sees snap-shots of the development of this cosmos alongside the development of the Argo’s journey, which creates an analogous progression between the two. Particularly salient for this thesis is the connection to Empedoclean ideas of love and strife as cosmic forces, as these comprise two of the major themes of the narrative. Accordingly, a key point of contact between narrative and cosmology lies in these forces, as the narrator consciously recalls them and the cosmos they control in the process of weaving his narrative. The three passages I examine all focus on this cosmic system, as the cosmic backdrop evolves and changes alongside the narrative itself. The cosmic analogy, therefore, is not static but changes in line with the narrative. This study will form the only extended analysis of cosmology in the Argonautica. The influence of cosmological material on the text (within the wider issue of philosophical influence) has attracted marginal attention, scholars often noting some of the more overt connections without a great deal of analysis. Works that acknowledge the presence of cosmological material at sporadic points include: Fränkel (1968); Hunter (1989 and 1993), Clauss (1993 and 2000); Levin (1970 and 1971). More detailed studies of aspects of cosmological material in the Argonautica include: Bogue (1979); Nelis (1992); Kyriakou (1994); Pendergraft (1995); Murray (2014); Santamaría Álvarez (2014). These studies all confirm the importance of cosmological ideas on the text, but focus on a particular manifestation of these ideas. This thesis will build on these ideas in an attempt to create a cohesive study of cosmology throughout the narrative and consider how this material affects our reading of the narrative itself and its poetic agenda, along with how this use feeds into Apollonius’ poetic values and contemporary poetic trends in general. The thesis is divided into three main chapters, in which I examine three key passages of the Argonautica to make my argument. In Chapter One I examine Orpheus’ song (1.496-511), in which the cultic bard Orpheus calms a fight between two Argonauts by singing a cosmogony. The song establishes cosmic forces that run analogous to the forces at work in the narrative and demonstrates how the growing influence of love in the cosmos parallels the increased reliance on love for the success of the Argonauts’ mission. In Chapter Two I examine Jason’s cloak (1.721-767), a passage that comprises the only extended ecphrasis in the Argonautica. The images woven into his cloak continue the cosmic theme begun in the song of Orpheus, since they demonstrate the world in a later stage of development, as human and divine events unfold and time progresses towards the Argonauts’ contemporary world. In Chapter Three I examine Eros’ sphere (3.129-141), an intricate toy offered to him by Aphrodite in exchange for his shooting Medea with an arrow to make her fall in love with Jason. The ball’s shape and its details both suggest that what Eros holds in his hand is some sort of divine three-dimensional model of the universe. I have chosen these three passages because a cosmological mode of reading is particularly strong in them; they bring to the forefront the cosmological undertone which underlies the wider narrative. My conclusion is that the three passages are all connected throughout the narrative by their cosmic material, material which underscores the Argonauts’ narrative and facilitates them anchoring their time to the grand timeframe of the cosmos. Both cosmic and narrative events run concurrently, as the evolution of the cosmos from its origins to the Argonauts’ present day runs alongside the evolution of the narrative. This duality shows how the Argonautic poet employs cosmology and in doing so creates a continuous parallel narrative that runs throughout the text. Since he uses three connected parallel narratives (song, garment, and toy), the reflective capacity of the passages is not merely a one-off, but consecutive, as all three comprise different moments in the same cosmic scheme. The boundaries between parallel narrative and main narrative are thus broken down in the passages as the narrator establishes the idea that cosmology does not only run parallel to the events of the narrative, but prefigures them and enriches the reader’s understanding of the narrative world. In sum, the cosmic readings of the passages demonstrate that what the narrator is drawing the reader towards is a cosmic subtext that is unfixed and undergoes change.

As the largest gravitationally bound objects in the Universe, galaxy clusters can be used to probe a variety of topics in astrophysics and cosmology. This thesis describes the development of an algorithm to find galaxy clusters using non-parameteric methods applied to catalogs of galaxies generated from multi-colour CCD observations. It is motivated by the emergence of increasingly large, photometric galaxy surveys and the measurement of key cosmological parameters through the evolution of the cluster mass function. The algorithm presented herein is a reconstruction of the successful, spectroscopic cluster finding algorithm, C4 (Miller et al., 2005), and adapting it to large photometric surveys with the goal of applying it to data from the Dark Energy Survey (DES). AperC4 uses statistical techniques to identify collections of galaxies that are unusually clustered in a multi-dimensional space. To characterize the new algorithm, it is tested with simulations produced by the DES Collaboration and I evaluate its application to photometric datasets. In doing so, I show how AperC4 functions as a cosmology independent cluster finder and formulate metrics for a \successful" cluster finder. Finally, I produce a galaxy catalog appropriate for statistical analysis. C4 is applied to the SDSS galaxy catalog and the resulting cluster catalog is presented with some initial analyses.