Despite the many successes of the current standard model of cosmology on the largest physical scales, it relies on two phenomenologically motivated constituents, cold dark matter and dark energy, which account for approximately 95% of the energy-matter content of the universe. From a more fundamental point of view, however, the introduction of a dark energy (DE) component is theoretically challenging and extremely fine-tuned, despite the many proposals for its dynamics. On the other hand, the concept of cold dark matter (CDM) also suffers from several issues such as the lack of direct experimental detection, the question of its cosmological abundance and problems related to the formation of structure on small scales. A perhaps more natural solution might be that the gravitational interaction genuinely differs from that of general relativity, which expresses itself as either one or even both of the above dark components. Here we consider different possibilities on how to constrain hypothetical modifications to the gravitational sector, focusing on the subset of tensor-vector-scalar (TeVeS) theory as an alternative to CDM on galactic scales and a particular class of chameleon models which aim at explaining the coincidences of DE. Developing an analytic model for nonspherical lenses, we begin our analysis with testing TeVeS against observations of multiple-image systems. We then approach the role of low-density objects such as cosmic filaments in this framework and discuss potentially observable signatures. Along these lines, we also consider the possibility of massive neutrinos in TeVeS theory and outline a general approach for constraining this hypothesis with the help of cluster lenses. This approach is then demonstrated using the cluster lens A2390 with its remarkable straight arc. Presenting a general framework to explore the nonlinear clustering of density perturbations in coupled scalar field models, we then consider a particular chameleon model and highlight the possibility of measurable effects on intermediate scales, i.e. those relevant for galaxy clusters. Finally, we discuss the prospects of applying similar methods in the context of TeVeS and present an ansatz which allows to cast the linear perturbation equations into a more convenient form.

There is a growing consensus among physicists that the classical notion of spacetime has to be drastically revised in order to nd a consistent formulation of quantum mechanics and gravity. One such nontrivial attempt comprises of replacing functions of continuous spacetime coordinates with functions over noncommutative algebra. Dynamics on such noncommutative spacetimes (noncommutative theories) are of great interest for a variety of reasons among the physicists. Additionally arguments combining quantum uncertain-ties with classical gravity provide an alternative motivation for their study, and it is hoped that these theories can provide a self-consistent deformation of ordinary quantum field theories at small distances, yielding non-locality, or create a framework for finite truncation of quantum field theories while preserving symmetries. In this thesis we study the gauge theories on noncommutative Moyal space. We nd new static solitons and instantons in terms of the so-called generalized Bose operators (GBO). GBOs are constructed to describe reducible representation of the oscillator algebra. They create/annihilate k-quanta, k being a positive integer. We start with giving an alternative description to the already found static magnetic flux tube solutions of the noncommutative gauge theories in terms of GBOs. The Nielsen-Olesen vortex solutions found in terms of these operators also reduce to the ones known in the literature. On the other hand, we nd a class of new instanton solutions which are unitarily inequivalent to the ones found from ADHM construction on noncommutative space. The charge of the instanton has a description in terms of the index representing the reducibility of the Fock space representation, i.e., k. After studying the static soliton solutions in noncommutative Minkowski space and the instanton solutions in noncommutative Euclidean space we go on to study the implications of the time-space noncommutativity in Minkowski space. To understand it properly we study the time-dependent transitions of a forced harmonic oscillator in noncommutative 1+1 dimensional spacetime. We also provide an interpretation of our results in the context of non-linear quantum optics. We then shift to the so-called DSR theories which are related to a different kind of noncommutative ( -Minkowski) space. DSR (Doubly/Deformed Special Relativity) aims to search for an alternate relativistic theory which keeps a length/energy scale (the Planck scale) and a velocity scale (the speed of light scale) invariant. We study thermodynamics of an ideal gas in such a scenario. In first chapter we introduce the subjects of the noncommutative quantum theories and the DSR. Chapter 2 starts with describing the GBOs. They correspond to reducible representations of the harmonic oscillator algebra. We demonstrate their relevance in the construction of topologically non-trivial solutions in noncommutative gauge theories, focusing our attention to flux tubes, vortices, and instantons. Our method provides a simple new relation between the topological charge and the number of times the basic irreducible representation occurs in the reducible representation underlying the GBO. When used in conjunction with the noncommutative ADHM construction, we nd that these new instantons are in general not unitarily equivalent to the ones currently known in literature. Chapter 3 studies the time dependent transitions of quantum forced harmonic oscillator (QFHO) in noncommutative R1;1 perturbatively to linear order in the noncommutativity . We show that the Poisson distribution gets modified, and that the vacuum state evolves into a \squeezed" state rather than a coherent state. The time evolutions of un-certainties in position and momentum in vacuum are also studied and imply interesting consequences for modelling nonlinear phenomena in quantum optics. In chapter 4 we study thermodynamics of an ideal gas in Doubly Special Relativity. We obtain a series solution for the partition function and derive thermodynamic quantities. We observe that DSR thermodynamics is non-perturbative in the SR and massless limits. A stiffer equation of state is found. We conclude our results in the last chapter.

Šimon Knoška The spherically symmetric spacetimes represent one of the most important classes of solutions in general relativity. Therefore, it is very natural to study them also in the context of modified theories of gravity. We directly continue in the previous works in quadratic gravity, where the generalised solutions with the constant Ricci scalar were found in the form of power series expansion in the conformal coordinates. In this work, we have found an alternative expression of this solution in the Robinson-Trautman-like coordinates analogously in the form of power series expansion around the horizon. Al- though the prescribed recurrent power series solution is more complicated than that in the conformal-to-Kundt coordinates, it posses numerous advantages. Namely, the trans- formation to the Schwarzschild-like coordinates is considerable simple and the physical interpretation of the coordinates is more evident. These properties are demonstrated in the preliminary investigation of the geodesic motion of the test particles near the black hole with analysis of the effect of the so-called Bach parameter. In particular, we have observed that the Bach parameter together with the positive cosmological constant Λ > 0 has a significant impact on the global structure of the spacetime.

Cette thèse se consacre premièrement à certains aspects de la définition de charges conservées en relativité générale pour les espaces asymptotiquement plats à l’infini spatial. À l’aide de la dualité gravitationnelle, présente au niveau linéarisé, on étudie également l’existence de charges topologiques, magnétiques, ainsi que leurs contributions aux superalgèbres dans les théories de supergravité N = 1 et N = 2 à quatre dimensions. La thèse est divisée en trois parties.<p>Dans la première partie, les espaces asymptotiquement plats à l’infini spatial sont décrits à l’aide d’une généralisation de la métrique de type Beig-Schmidt. La construction de charges à partir de l’étude des équations du mouvement et de la classification de tenseurs symétriques et de divergences nulles nous permet de démontrer l’unicité des charges de Poincaré pour l’ansatz non-généralisé en présence de conditions de parité. L’équivalence des charges de Ashtekar- Hansen et Mann-Marolf est ainsi revisitée. Dans le cas d’un ansatz généralisé, une régulation de la forme symplectique divergente, à l’aide de contre-termes rajoutés à l’action de Mann-Marolf, nous donne la possibilité de considérer un espace des phases sans conditions de parité, tout en gardant un principe variationnel bien défini. Le groupe asymptotique comprend alors, en plus des charges de Poincaré où les charges de Lorentz ne sont plus asymptotiquement linéaires, des charges non-triviales associées aux supertranslations et aux transformations logarithmiques.<p>Dans la deuxième partie, on étudie la dualité gravitationnelle et la définition de charges magnétiques en gravitation linéarisée. On revisite la dualité et on montre qu’une dualisation sur les indices de Lorentz facilite la compréhension de celle-ci. Les dix charges de Poincaré ainsi que leurs duales magnétiques sont alors exprimées en termes d’intégrales de surface. Nous illustrons ensuite nos résultats à travers l’étude des sources de certaines solutions électriques et de leur duales magnétiques. Les solutions électriques envisagées sont :les trous noirs de type Schwarzschild et de type Kerr ainsi que les ondes de chocs de type pp.<p>Dans la dernière partie, on établit la supersymétrie des espaces de type Taub-NUT lorentzien chargés électriquement et magnétiquement dans la supergravité N = 2. Motivé par l’existence d’une égalité BPS, on entreprend alors une recherche sur l’inclusion de la charge NUT dans l’algèbre de supersymétrie. Grâce à une complexification de la forme de Witten-Nester, cette contribution de la charge NUT à la superalgèbre est comprise comme une déformation topologique, symétrique, au crochet antisymétrique des super-charges. Ce résultat est alors appliqué à la superalgèbre N = 1 à travers l’étude des ondes de chocs de type pp.<p> / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

Dans cette thèse nous analysons la place logique que les principes ont occupée à la fin du XIXe et au début du XXe siècle dans la construction des théories relativistes. Après une présentation de caractère général et historique (chapitres 1-3) dans laquelle nous rappelons le statut des principes dans la tradition classique et dans les travaux de Newton, et dans laquelle nous tentons de montrer comment la théorie de la thermodynamique et les théories de la lumière ont pu remettre en cause cette tradition, le corpus de la thèse peut être divisé en deux grandes parties, une première (chapitres 4-6) consacrée à la relativité restreinte, et une deuxième (chapitres 7-9) consacrée à la théorie de la relativité générale. Le chapitre 1 est consacré à rappeler ce que sont les principes dans la tradition classique, d’Aristote à Galilée et Newton. Dans le deuxième chapitre nous évoquons la formulation des deux principes de la thermodynamique et nous montrons en quoi ils s’éloignent de la mécanique classique et peuvent être considérés comme deux principes d’un nouveau type. Dans le troisième chapitre nous présentons un panorama des théories physiques à la fin du XIXe siècle, afin de replacer dans leur contexte les réflexions qui ont conduit à la formulation de la théorie de la relativité restreinte. Les chapitres quatre et cinq sont consacrés au principe de relativité. Dans le chapitre quatre nous l’abordons de façon géométrique, en mettant en évidence les différences entre espace géométrique et espace physique et les problèmes liés à l’espace absolu. Au chapitre cinq nous analysons de plus près la formulation du principe de relativité dans les travaux de Poincaré de 1904-1905. Le chapitre six est consacré à la présentation de la relativité restreinte faite par Einstein la même année 1905. Les chapitres sept, huit et neuf sont consacrés à la relativité générale et aux principes qu’Einstein pose à sa base. Dans le chapitre sept nous analysons le principe d’équivalence et la première période de formulation de la théorie de la relativité générale (1907-1912). Le chapitre 8 reprend le thème de la géométrie et montre comment des considérations générales sur la non-validité de la géométrie euclidienne ont mis Einstein sur la voie de la théorie généralisée de la gravitation. Le chapitre 9 aborde un moment délicat de la construction de la théorie :les années 1913-1915, pendant lesquelles Einstein abandonne l’idée de covariance générale et essaie d’établir les équations de la théorie. Nous analysons les principes qui le guident dans ses recherches et ceux qu’il abandonne (même temporairement), pour montrer enfin comment Einstein est arrivé à la formulation de la théorie de la relativité générale. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

Master of Science / Department of Physics / Bharat Ratra / In this report, we discuss the four standard energy conditions of General Relativity (null, weak, dominant, and strong) and investigate their cosmological consequences. We note that these energy conditions can be compatible with cosmic acceleration provided that a repulsive cosmological constant exists and the acceleration stays within certain bounds. Scalar fields and dark energy, and their relationships to the energy conditions, are also discussed. Special attention is paid to the 1988 Ratra-Peebles scalar field model, which is notable in that it provides a physical self-consistent framework for the phenomenology of dark energy. Appendix B, which is part of joint-research with Anatoly Pavlov, Khaled Saaidi, and Bharat Ratra, reports on the existence of the Ratra-Peebles scalar field tracker solution in a curvature-dominated universe, and discusses the problem of investigating the evolution of long-wavelength inhomogeneities in this solution while taking into account the gravitational back-reaction (in the linear perturbative approximation).

In this thesis, I study the relativistic effects of matter inhomogeneities on the accelerating expansion of the Universe. The acceleration is often taken to be caused by the presence of an exotic fluid called Dark Energy, or else a non-zero 'cosmological constant' term in the field equations of General Relativity. I consider whether this result could instead be an artefact caused by using an incorrect model to interpret observations. The standard 'concordance' cosmological model assumes the Cosmological Principle, which states that the matter distribution on large scales is homogeneous. One possibility is that correction terms appear in the field equations when small-scale inhomogeneities are smoothed over to produce this homogeneous model. These 'backreaction' effects could affect the dynamics of the spacetime, causing an apparent acceleration. I clarify the relationship between acceleration of the averaged spacetime and acceleration inferred from observable quantities, and show that they are closely related in statistically-homogeneous spacetimes. Another possibility is that the Universe could be inhomogeneous on large scales. If there was a large ‘void’, with us at the centre, the lensing of light by the void could reproduce the observations that imply cosmic acceleration. I show that a popular class of void models, based on spherically-symmetric Lemaitre-Tolman-Bondi spacetimes, are unable to simultaneously fit a selection of observational data, thus effectively ruling-out this possibility. These data include the Kinematic Sunyaev-Zel'dovich (KSZ) effect, which is a distortion/shift of the Cosmic Microwave Background (CMB) frequency spectrum caused by the Compton scattering of photons by hot gas in galaxy clusters. This, and other distortions of the CMB frequency spectrum, are sensitive to the degree of anisotropy in the CMB about a scattering cluster. I suggest tests involving these observables that exploit the strong link between isotropy and homogeneity to (a) distinguish between different causes of a deviation from spatial flatness on the horizon scale, and (b) potentially confirm the Cosmological Principle using observations. Finally, I describe a novel Bayesian CMB component separation method for extracting the Sunyaev-Zel'dovich signal of clusters from CMB sky maps.

Compilation of two papers, the first of which was accepted for publication in the South African Journal of Philosophy in the second half of 2001. / Why metaphors have no meaning : considering metaphoric meaning in Davidson. -- Bare idea of a conceptual scheme : relativism, intercultural communication and Davidson. / Thesis (MA)--Stellenbosch University, 2000. / ENGLISH ABSTRACT: WHY METAPHORS HAVE NO MEANING: CONSIDERING METAPHORIC MEANING IN DAVIDSON Since the publication of Donald Davidson's essay 'What Metaphors Mean' (1984c) - in which he famously asserts that metaphor has no meaning - the views expressed in it have mostly met with criticism: prominently from Mary Hesse and Max Black. This article attempts to explain Davidson's surprise-move regarding metaphor by relating it to elements in the rest of his work in semantics, such as the principle of compositionality, radical interpretation and the principle of charity. I conclude that Davidson's views on metaphor are not only consistent with his semantic theory generally, but that his semantics also depend on these insights. Eventually, the debate regarding Davidson's views on metaphor should be conducted on the level of his views on the nature of semantics, the relationship between language and the world and the possibility of there existing something like conceptual schemes. / ENGLISH ABSTRACT: THE BARE IDEA OF A CONCEPTUAL SCHEME: RELATIVISM, INTERCULTURAL COMMUNICATION AND DAVIDSON Donald Davidson's paper 'On the Very Idea of a Conceptual Scheme' ('OVICS') has become famous for the refutation accomplished in it of conceptual relativism. Via an argument that, essentially, all languages are intertranslatable, Davidson rejects the notion that different conceptual schemes can inhere in the supposed 'un-translatable' languages said to exist by, for instance, Whorf and Kuhn. Critics of Davidson's position have mainly focussed on practical issues, with many holding that his arguments in 'OVICS' ignore the realities of the real intercultural communication situation. In the present paper, I address criticisms of this sort. Davidson's arguments are reconstructed, with attention being paid to their dependence on the idea of practical application in the real intercommunication situation. With the aid of practical examples, the implications of elements of Davidson's philsophy of interpretation for intercultural communication are evaluated. Finally, radical interpretation is presented as a better model for intercultural dialogue than linguistically relativist ones. / AFRIKAANSE OPSOMMING: WHY METAPHORS HAVE NO MEANING: CONSIDERING METAPHORIC MEANING IN DAVIDSON Sedert die publikasie van Donald Davidson se opstel 'What Metaphors Mean' (1984c) - waarin hy die berugte stelling maak dat metafoor geen betekenis het nie - is sy sieninge meestal begroet met kritiek, ook van prominente figure soos Mary Hesse en Max Black. Hierdie artikel poog om 'n verduideliking te vind vir Davidson se verassende skuif aangaande metafoor, deur sy sieninge hieroor te kontekstualiseer teen die agtergrond van elemente uit die res van sy werk in semantiek, soos die beginsel van komposisionaliteit, radikale interpretasie en die beginsel van rasionele akkomodasie ('charity'). Ek kom tot die gevolgtrekking dat Davidson se sieninge aangaande metafoor nie slegs naatloos aansluit by sy algemene sieninge aangaande semantiek nie, maar dat die res van sy semantiese teorie ook afhang van sy sieninge aangaande metafoor. Uiteindelik behoort die debat rakende Davidson se sieninge aangaande metafoor gevoer te word op die vlak van die aard van semantiek, die verhouding tussen taal en die werklikheid en die moontlike bestaan van konseptueie skemas. / AFRIKAANSE OPSOMMING: THE BARE IDEA OF A CONCEPTUAL SCHEME: RELATIVISM, INTERCULTURAL COMMUNICATION AND DAVIDSON Donald Davidson se artikel 'On the Very Idea of a Conceptual Scheme' het beroemdheid verwerf as teenargument vir die idee van konseptuele relativisme. By wyse van 'n argument dat alle tale in beginsel vertaalbaar is, verwerp Davidson die idee dat verskillende konseptueie skemas kan skuilgaan in die veronderstelde 'onvertaalbare' tale waarvan daar sprake is by byvoorbeeld Whorf en Kuhn. Kritici van Davidson se posisie beperk hul hoofsaaklik tot praktiese besware en 'n vername aanklag teen Davidson is dat hy die realiteite misken van werklike interkulturele gesprek. In hierdie artikel spreek ek sodanige kritiek aan. Ek herkonstrueer Davidson se argumente en voer aan dat dit deurgaans afhanklik is van die idee van toepassing in 'n praktiese situasie van interkulturele dialoog. By wyse van praktiese voorbeelde evalueer ek die implikasies van Davidson se filosofie van interpretasie vir interkulturele kommunikasie. Laastens bied ek radikale interpretasie aan as 'n beter model vir interkulturele dialoog as linguisties relativistiese modelle.

無庸置疑，人類的每一項知覺都一樣重要。因為我們仰賴這些知覺接收來自周遭的訊息，只要有一個消失不見，我們在生活上便會遇到困難。然而，在語言表達上，知覺並非一樣重要。嗅覺看似是最難表達的知覺，因為人們常常依賴物體來表達嗅覺，例如「草的味道」。另一方面，我們無需依賴物體、並使用顏色來表達視覺。當我們想陳述對於「天空」的想法時，我們會使用「藍色」而不是「天空的顏色」。不同的語言有無可能把重點放在不同的知覺上？如果是，是什麼原因造成不同的語言現象？ 觀察人們如何表達對食物的看法非常適合用來討論知覺表達，因為品嚐食物的過程和視覺、嗅覺、味覺、及口感息息相關。本研究搜集來自中文及日文母語者有關食物的知覺表達，包括職業廚師及料理新手。米飯在中國及日本文化扮演著主食的角色，這項文化地位讓米飯成為與發音人面談上的主題。假設所有的知覺在不同文化都一樣重樣，人們應該會以相似的方式來表達知覺。研究結果發現在知覺表達中，中文母語者主要強調口感，但日語母語者強調視覺。透過比較職業廚師及料理新手也能找到知覺表達上的差異：職業廚師主要著重視覺，新手則重視味覺。人們亦使用不同的認知策略來表達不同知覺，但職業廚師及新手都依賴對食物的評價來表達知覺。從生理學上來看，人類的知覺一樣重要，但中文及日文的知覺表達卻不一樣。本研究認為文化及社會因素了影響語言的知覺表達。 / Senses are undoubtedly important to people because they allow us to experience our world and we would face difficulties when any of them were absent. However, senses are not equally important in linguistic expressions. It seems that expressing odors is difficult in some languages because people often rely on concrete objects to make olfactory expressions, such as cǎo de weìdào ‘the smell of grass.’ Making use of color rather than concrete objects for visual expressions, we often choose lán ‘blue’ rather than tiānkōng de yánsè ‘the color of sky’ when expressing what we feel from sky. Is it possible that different emphasis of senses can be observed in different languages? If so, what is the reason leading to the differences in languages? Observing how people express their feeling toward food is an appropriate method to discuss sensory expressions, because the procedure of tasting food is strongly correlated with multiple senses like vision, odor, taste, and mouthfeel. This study collects sensory expressions of food from both Chinese and Japanese speakers, including both experts and novices of cooking. Acting as the main dish in Chinese and Japanese cultures, rice is regarded as the theme of interview due to the cultural importance. If all senses are important in different cultures, they should be expressed in similar ways. Our results suggest that Chinese mainly focuses on mouthfeel, while Japanese mainly focuses on vision when performing sensory expressions. The differences in sensory expressions can also be observed through comparing experts with novices: experts mainly focus on vision, and novices firstly choose taste. People also make use of different cognitive strategies to express different kinds of senses, but both experts and novices rely on the evaluative type to create sensory expressions. Sensory expressions are different between Chinese and Japanese although senses are physiologically identical for people. This study suggests that both culture and social factors influence sensory expressions in languages.

I modify the quasilocal energy formalism of Brown and York into a purely Hamiltonian form. As part of the reformulation, I remove their restriction that the time evolution of the boundary of the spacetime be orthogonal to the leaves of the time foliation. Thus the new formulation allows an arbitrary evolution of the boundary which physically corresponds to allowing general motions of the set of observers making up that boundary. I calculate the rate of change of the quasilocal energy in such situations, show how it transforms with respect to boosts of the boundaries, and use the Lanczos-Israel thin shell formalism to reformulate it from an operational point of view. These steps are performed both for pure gravity and gravity with attendant matter fields. I then apply the formalism to characterize naked black holes and study their properties, investigate gravitational tidal heating, and combine it with the path integral formulation of quantum gravity to analyze the creation of pairs of charged and rotating black holes. I show that one must use complex instantons to study this process though the probabilities of creation remain real and consistent with the view that the entropy of a black hole is the logarithm of the number of its quantum states.