In this thesis a set of recently proposed multigravity theories is analysed. In the special case of bimetric gravity, the theory has been conclusively shown to be ghost-free. On the other hand, for multigravity theories in general, the ghost-issue has not been settled conclusively. Motivated by this fact, the main object of this thesis is to clarify what has been proven so far and what issues that still needs to be addressed. We also provide new calculations and results pointing in the direction that the multigravity theories must be restricted to a set of bimetric Hassan-Rosen couplings in a tree-type structure in order to be consistent. In particular, we prove that for a multivielbein theory of <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5Cmathscr%7BN%7D" /> interacting vielbeins, the Lorentz equations of motion is a set of <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?(%5Cmathscr%7BN%7D-1)" /> Deser-van Nieuwenhuizen conditions if and only if the theory consists of bimetric Hassan-Rosen couplings in a tree-type structure.

The effect of excess gravity on bone-forming elements of the growing perichondrial shaft of embryonic chicks was investigated through the use of the transmission electron microscope and various cytochemical techniques.

Ein neues Schema für die Parametrisierung der Schwerewellen und ihres Einflusses auf die mittlere Atmosphäre ist für COMMA-LIM (COlogne Model of the Middle Atmosphere - Leipzig Institute for Meteorology) übernommen worden. Während das bisher in COMMA-LIM genutzte aktualisierte Lindzen-Schema (Lindzen, 1981) die Ausbreitung und das Brechen einzelner Wellen berechnet, geht das Warner und McIntyre-Schema von einem Spektrum der Schwerewellen aus. Beide Schemata gehen von Schwerewellen im mittleren Frequenzbereich zwischen Brunt-Väisäla Frequenz und Rotationsrate der Erde aus (N >> ω >> f). Erste Ergebnisse werden vorgestellt. / A new scheme for the parametrizing of the gravity waves and their impact on the mean circulation of the middle atmosphere has been adapted to COMMA-LIM (COlogne Model of the Middle Atmosphere - Leipzig Institute for Meteorology). The current version based on the Lindzen-scheme (Lindzen, 1981) calculates the propagation and breaking of 48 single waves while the new Warner and McIntyre - scheme uses a spectral approach of gravity waves. Both schemes are based on the medium frequency approach locating the gravity waves between the Brunt-Väisälä-frequency and the rotation rate of the earth ((N >> ω >> f). First results are presented.

This study is aim to evaluate the effect of five factors on the amount of tourists arrivals to China in those countries who have most visitors. To apply empirical estimation, a balanced panel data based gravity equation is established, with 22 countries and 15 years period (1998 - 2002). Our main estimates conclude that GDP per capita has a positive impact on the amount of tourists, as well as population, whereas exchange rate and distance will deter the amounts of tourists. Unfortunately PPP conversion factor also has a positive impact but not as expected. The findings of this study will fill the gap of relative literatures for China and provide another evidence of gravity model.

Les aquifères karstiques constituent l'essentiel des ressources en eau du pourtour Méditerranéen. Au delà de la zone saturée de ces systèmes, la zone non saturée constitue une entité importante quant au transfert et au stockage temporaire de l'eau. La structure et le fonctionnement de cette entité du karst sont complexes et mal connus à cause du processus de karstification qui hiérarchise la circulation hydrodynamique en son sein. Dans cette étude nous utilisons des méthodes géodésiques et hydrogéologiques afin d'observer de façon directe et de quantifier les processus de transfert et de stockage de la zone non saturée. Les mesures gravimétriques en surface et profondeur sur différents systèmes karstiques ont permis de quantifier les variations du stockage en eau saisonnier dans la zone non saturée. La gravimétrie différentielle montre que ces variations sont réparties dans les quelques premiers mètres de la zone non saturée. Il semble, de plus, que la capacité de stockage de la zone non saturée soit fonction de la lithologie de l'encaissant (calcaire et dolomie). Enfin, des observations directes du flux d'eau en zone non saturée ont été effectuées par le biais de mesures dans différentes cavités. Nous montrons que certaines caractéristiques du flux d'eau en zone non saturée, comme la présence d'un flux bipolaire lent-rapide, peuvent être généralisées quelques soit la profondeur de mesure et la surface d'impluvium. La modélisation de ce flux, à partir d'un schéma simple, a montré la complexité des processus de transfert engendrés au sein de la zone non saturée. / Karst systems are the most important groundwater reservoirs in Mediterranean area. Beyond saturated zone, unsaturated zone constitute an entity where water storage and transfer play a major role in a global behavior of spring water. This structure and functioning are complex and not well known because of the high heterogeneity created and organized by groundwater flow. In this study, we used gravimetric and hydrogeologic method to directly observe and quantify water storage and transfer processes in unsaturated zone of karst system. Surface to depth gravity measurements on several karst system allow quantifying seasonal water storage changes in unsaturated zone. We show that these variations occur in the first tens meters of unsaturated zone. Furthermore, water storage capacity of unsaturated zone seems to be influenced by lithology (limestone or dolomite). Finally, direct observations of water flow in unsaturated zone are done using caves access. We show that some characteristics of unsaturated water flow such as bipolar slow-fast flow can be widespread for whatever depth of measurement and recharge area. Model of this flow, using a simple modeling scheme, show the complexity of water transfer processes in unsaturated zone of karst system.

A thesis submitted to the Faculty of Science, University of the Witwatersrand, in fulfilment of the requirements for the degree of Doctor of Philosophy. 3rd October 2013. / A complete understanding of quantum gravity remains an open problem. However, the AdS/CFT correspondence which relates quantum eld theories that enjoy conformal symmetry to theories of (quantum) gravity is proving to be a useful tool in shedding light on this formidable problem. Recently developed group representation theoretic methods have proved useful in understanding the large N; but non-planar limit of N = 4 supersymmetric Yang-Mills theory. In this work, we study operators that are dual to excited giant gravitons, which corresponds to a sector of N = 4 super Yang-Mills theory that is described by a large N; but non-planar limit. After a brief review of the work done in the su (2) sector, we compute the spectrum of anomalous dimensions in the su (2) sector of the Leigh-Strassler deformed theory. The result resembles the spectrum of a shifted harmonic oscillator. We then explain how to construct restricted Schur polynomials built using both fermionic and bosonic elds which transform in the adjoint of the gauge group U (N) : We show that these operators diagonalise the free eld two point function to all orders in 1=N: As an application of our new operators, we study the action of the one-loop dilatation operator in the su (2,3) sector in a large N; but non-planar limit of N = 4 super Yang-Mills theory. As in the su (2) case, the resulting spectrum matches the spectrum of a set of decoupled oscillators. Finally, in an appendix, we study the action of the one-loop dilatation operator in an sl (2) sector of N = 4 super Yang-Mills theory. Again, the resulting spectrum matches that of a set of harmonic oscillators. In all these cases, we nd that the action of the dilatation operator is diagonalised by a double coset ansatz.

A crescente demanda por informações gravimétricas consistentes em âmbito sul-americano, visando, sobretudo, a unificação de um sistema altimétrico para o continente, foi a motivação maior deste trabalho. Nesse contexto, procurou-se evidenciar informações detalhadas, de cunho técnico e operacional, voltadas à execução de levantamentos gravimétricos. Assim, conceitos básicos introdutórios seguidos de uma resenha histórica da gravimetria no Brasil e no mundo, são delineados. É efetuada a proposta de uma nova abordagem para um sistema gravimétrico. Apresentam-se aspectos práticos detalhados sobre o manuseio do gravímetro LaCoste & Romberg. Sugerem-se, adicionalmente, procedimentos metodológicos para as diversas etapas de uma operação gravimétrica. Ao final, à guisa de estudo de caso, disponibilizam-se resultados que são analisados e comparados. / The increasing demand for consistent South American gravimetric informations, aiming, most of all, the unification of a height system for the continent, was the motivation for this work. Within this context, an effort was made to evince detailed technical and operational informations related to the execution of gravimetric surveys. Basic concepts are exposed, followed by a historical summary of gravimetry in Brazil and throughout the world. A proposal of a new approach for a gravimetric system is made and detailed practical aspects on the use of LaCoste & Romberg gravity meter are given. In addition, methodological procedures are suggested for the several stages of a gravimetric operation. Finally, as a case study, results are made available after analysis and comparisons.

Holographic dualities are now an established tool in the study of universal properties of strongly coupled field theories. Yet, theories without translational symmetry are still poorly understood in this context. In this dissertation, we investigate three new approaches to this challenging problem. The first part of the dissertation concerns a class of phenomenological holographic models in which momentum relaxation can be achieved without breaking translational symmetry in the dual geometry. In particular, we focus on an example in which the dual geometry is similar to anti-de Sitter (AdS) Brans-Dicke theory. We study the thermodynamic and transport properties of the model and show that for strong momentum relaxation and low temperatures the model has insulator-like behaviour. In the second part, we go beyond the effective description and consider holographic theories which explicitly break translational symmetry. From the perspective of gravity, these theories translate to geometries that vary explicitly in the boundary space-like coordinates. We refer to these geometries as 'inhomogeneous' and investigate two approaches to study them. The first is motivated by the question: "what happens to a homogeneous geometry when coupled with a field varying randomly in space?". Starting from an AdS geometry at zero or finite temperature, we show that a spatially varying random Maxwell potential drives the dual field theory to a non-trivial infra-red fixed point characterised by an emerging scale invariance. Thermodynamic and transport properties of this disordered ground state are also discussed. The second is motivated by the complementary question: "how does a random geometry affect a probe field?". In the weak disorder limit, we show that disorder induces an additional power-law decay in the dual correlation functions. For certain choices of geometry profile, this contribution becomes dominant in the infra-red, indicating the breaking of perturbation theory and the possible existence of a phase transition induced by disorder. The third and last part of this dissertation switches from the gravity to the field theoretical side of the duality. We discuss the Sachdev-Ye-Kitaev (SYK) model, a disordered many-body model with distinctive black hole-like properties. We provide analytical and numerical evidence that these holographic properties are robust against a natural one-body deformation for a finite range of parameters. Outside this interval, this system undergoes a chaotic-integrable transition.

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.

The inner regions of discs around close binary systems are dominated by tidally truncated eccentric cavities. These are believed to play a key role in dictating where planets formed in these circumbinary discs halt their disc-driven migration. In this thesis we present work examining processes which could impact the evolution and structure of this region, and the planets which interact with it. First, we investigate the role of self-gravity and disc-mass on circumbinary discs and planets. The greatest impact of self-gravity was found in discs around highly eccentric binaries, and in discs with high masses. In these cases, self-gravity acts to compact the scale of the inner cavity region. For the highest disc masses, additional eccentric features arise in the outer disc. A range of scenarios examining planetary migration, accretion and disc dissipation find that if planets form and evolve in a high-mass environment, the disc structures formed by self-gravity can leave a fingerprint on the planetary architecture once the disc has dissipated. We also significantly modify the publicly available fargo-adsg hydrodynamical code, to include radiative effects such as disc irradiation by the binary stars, radiative transport and disc surface cooling. We present preliminary results of simulations of adiabatic circumbinary discs with these effects included, and consider also the migration of protoplanets within them. Fully radiative discs produce a smaller inner cavity than obtained in previous isothermal models - a promising result for the end point of planet migration in these discs. Whilst we have found significant alteration of the circumbinary enviroment by self-gravity and radiative effects, future simulations that capture the 3-D nature of these discs will be required to fully describe the observed architecture of the circumbinary systems.