Dissertations / Theses on the topic 'Brand gravity'

The cosmology in the Hubble expansion era of the Horava-Witten M-theory compactified on a Calabi-Yau threefold is studied in the reduction to five-dimensions where the effects of the Calabi-Yau manifold are summarized by the volume modulus, and all perturbative potentials are included. Matter on the branes are treated as first order perturbations of the static vacuum solution, and all equations in the bulk and all boundary conditions on both end branes are imposed. It is found that for a static volume modulus and a static fifth dimension, y, one can recover the four dimensional Robertson-Friedmann-Walker cosmology for relativistic matter on the branes, but not for non-relativistic matter. For relativistic matter, the Hubble parameter H becomes independent of y to first order in matter density, and if a consistent solution for nonrelativistic matter exists it would require H to be y dependent. These results hold also when an arbitrary number of 5-branes are included in the bulk. The five dimensional Horava-Witten model is compared with the Randall Sundrum phenomenology with a scalar field in the bulk where a bulk and brane potential are used so that the vacuum solutions can be rigorously obtained.(In the Appendix, the difficulty of obtaining approximate vacuum solutions for other potentials is discussed.) In this case nonrelativistic matter is accommodated by allowing the distance between the branes to vary. It is suggested that non-perturbative potentials for the vacuum solution of Horava-Witten theory are needed to remove the inconsistency that non-relativistic matter creates. Also considered is the problem of gravitational forces between point particles on the branes in a Randall-Sundrum (R-S) two brane model with S1/Z2 symmetry. Matter is assumed to produce a perturbation to the R-S vacuum metric and all the 5D Einstein equations are solved to linearized order (for arbitrary matter on both branes). We show that while the gauge condition hi5 = 0, i = 0, 1, 2, 3 can always be achieved without brane bending, the condition h55 = 0 leads to large brane bending. The static potential arising from the zero modes and the corrections due to the Kaluza-Klein (KK) modes are calculated. Gravitational forces on the Planck (y1 = 0) brane recover Newtonian physics with small KK corrections (in accord with other work). However, forces on the TeV (y2) brane due to particles on that brane are strongly distorted by large R-S exponentials, making the model in disagreement with experiment if the TeV brane is the physical brane.

We examine the use of branes as probes of supergravity geometries which arise in the study of gauge theory/gravity dualities. We investigate the moduh spaces of supersymmetric gauge theories through moduh spaces of brane probes in the dual gravity theories. Preferred coordinate systems emerge in which the supergravity geometries can readily be compared to the gauge theory and various gauge theory quantities such as anomalous scaling dimensions can be read off. We also consider the physics of certain expanded brane configurations, called giant gravitons. We identify supergravity solutions which represent coherent states of these objects. We find a degeneracy between giant graviton probes and massless particles in a broad class of supergravity backgrounds and uncover a close relationship with charged particle states in lower dimensions.

In Brans-Dicke gravity a scalar field non-minimally coupled with the curvature acts as a new gravitational degree of freedom in addition to the usual metric field of General Relativity. Usually, when the coupling ω of the scalar field diverges, the latter approaches a constant and the solutions of the theory reduce to those generated by the Einstein equations with the same energy-momentum tensor as source. However, in the limit ω → ∞, the static and spherically symmetric vacuum solutions, called Brans solutions, do not reduce to the Schwarzschild metric, the only solution of General Relativity with the same type of symmetry. In this work we test their limit with a new method. Unlike the usual way, we use the Brans solutions to take the limit at the level of the equations. Since these are non-linear field equations depending on ω, in principle our procedure could lead to a different outcome. In particular, we take advantage of the Einstein frame formulation of the Brans-Dicke theory and we check if the solutions are able to satisfy the equations of the so called Minimal Geometric Deformation approach. Namely, we study if they can be seen as a geometric deformation - due to the Brans-Dicke scalar - of the Schwarzschild solution. Indeed, the peculiar feature of the geometric deformation is that it is built in such a way to guarantee a clear limit to the vacuum equations of General Relativity. However, we find that the Brans solutions do not meet all the requirements imposed by the structure of the Minimal Geometric Deformation approach. This result supports the conclusion that there is no simple limiting procedure in which the complete Brans-Dicke theory just reduces to General Relativity.

Current research is focussed on extending our knowledge of how gravity behaves on small scales and near black hole horizons, with various modifications which may probe the low energy limits of quantum gravity. This thesis is concerned with such modifications to gravity and their implications. In chapter two thermodynamical stability analyses are performed on higher dimensional Kerr anti de Sitter black holes. We find conditions for the black holes to be able to be in thermal equilibrium with their surroundings and for the background to be stable against classical tensor perturbations. In chapter three new spherically symmetric gravastar solutions, stable to radial perturbations, are found by utilising the construction of Visser and Wiltshire. The solutions possess an anti de Sitter or de Sitter interior and a Schwarzschild (anti) de Sitter or Reissner Nordstrom exterior. We find a wide range of parameters which allow stable gravastar solutions, and present the different qualitative behaviors of the equation of state for these parameters. In chapter four a six dimensional warped brane world compactification of the Salam-Sezgin supergravity model is constructed by generalizing an earlier hybrid Kaluza Klein / Randall Sundrum construction. We demonstrate that the model reproduces localized gravity on the brane in the expected form of a Newtonian potential with Yukawa type corrections. We show that allowed parameter ranges include values which potentially solve the hierarchy problem. The class of solutions given applies to Ricci flat geometries in four dimensions, and consequently includes brane world realisations of the Schwarzschild and Kerr black holes as particular examples. Arguments are given which suggest that the hybrid compactification of the Salam Sezgin model can be extended to reductions to arbitrary Einstein space geometries in four dimensions. This work furthers our understanding of higher dimensional general relativity, which is potentially interesting given the possibility that higher dimensions may become observable at the TeV scale, which will be probed in the Large Hadron Collider in the next few years.

The gauge/string correspondence provides a non-perturbative definition of string theory and hence quantum gravity in some backgrounds, making it possible to translate statements about strongly coupled quantum field theories into results about gravity.

In this thesis, we focus on the derivation of holographic backgrounds from the field theory, without using any supergravity input. Instead, we rely crucially on the addition of probe D-branes to the stack of D-branes generating the background.

From the field theory description of the probe branes in the presence of the background branes, one can compute an effective action for the probes (in a suitable low-energy/near-horizon limit) by integrating out the background branes. Comparing this action with the D-brane probe action in a generic supergravity background then allows to determine the holographic background dual to the considered field theory vacuum.

In the first part, the required pre-requisites of field and string theory are recalled and this strategy to derive holographic backgrounds is explained in more detail on the basic case of D3-branes in flat space probed by a small number of D-instantons.

The second part contains the original results of this thesis, obtained by applying this strategy to several specific examples. We first derive the duals to three continuous deformations (Coulomb branch, β and non-commutative deformations) of the basic case, in the limit in which the D-instantons can probe the full geometry. We then derive the enhançon mechanism in a dual to a simple N=2 quiver gauge theory by using a fractional D-instanton as a probe and exploiting recent exact results on the Coulomb branch of N=2 quivers.

Finally, we obtain the near-horizon D4-brane geometry by probing the D4-branes with a small number of D0-branes.

Doctorat en Sciences
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General relativity (GR) has stood as the most accurate description of gravity for the last 100 years, weathering a barrage of rigorous tests. However, attempts to derive GR from a more fundamental theory or to capture further physical principles at high energies has led to a vast number of alternative gravity theories. The individual examination of each gravity theory is infeasible and as such a systematic method of examining modified gravity theories is a necessity. Studying generic classes of gravity theories allows for general statements about observables to be made independent of explicit models. Take, for example, those models described by the Horndeski action, the most general class of scalar-tensor theory with at most second-order derivatives in the equations of motion, satisfying theoretical constraints. But these constraints alone are not enough for a given modified gravity model to be physically viable and hence worth studying. In particular, observations place incredibly tight constraints on the size of any deviation in the solar system. Hence, any modified gravity would have to mimic GR in such a situation. To accommodate this requirement, many models invoke screening mechanisms which suppress deviations from GR in regions of high density. But these mechanisms really upon non-linear effects and so studying them in complex models is mathematically complex. To constrain the space of actions of Horndeski type to those which pass solar-system tests, a set of conditions on the four free functions of the Horndeski action are derived which indicate whether a specific model embedded in the action possesses a GR limit. For this purpose, a new and surprisingly simple scaling method is developed, identifying dominant terms in the equations of motion by considering formal limits of the couplings that enter through the new terms in the modified gravity action. Solutions to the dominant terms identify regimes where nonlinear terms dominate and Einstein's field equations are recovered to leading order. Together with an efficient approximation of the scalar field profile, one can determine whether the recovery of Einstein's field equations can be attributed to a genuine screening effect. The parameterised post-Newtonian (PPN) formalism has enabled stringent tests of static weak-field gravity in a theory-independent manner. This is through parameterising common perturbations of the metric found when performing a post-Newtonian expansion. The framework is adapted by introducing an effective gravitational coupling and defining the PPN parameters as functions of position. Screening mechanisms of modified gravity theories can then be incorporated into the PPN framework through further developing the scaling method into a perturbative series. The PPN functions are found through a combination of the scaling method with a post-Newtonian expansion within a screened region. For illustration, we show that both a chameleon and cubic galileon model have a limit where they recover GR. Moreover, we find the effective gravitational constant and all PPN functions for these two theories in the screened limit. To examine how the adapted formalism compares to solar-system tests, we also analyse the Shapiro time delay effect for these two models and find no deviations from GR insofar as the signal path and the perturbing mass reside in a screened region of space. As such, tests based upon the path light rays such as those done by the Cassini mission do not constrain these theories. Finally, gravitational waves have opened up a new regime where gravity can be tested. To this end, we examine how the generation of gravitational waves are affected by theories of gravity with screening to second post-Newtonian (PN) order beyond the quadrupole. This is done for a model of gravity where the black hole binary lies in a screened region, while the space between the binary's neighbourhood and the detector is described by Brans-Dicke theory. We find deviations at both 1.5 and 2 PN order. Deviations of this size can be measured by the Advanced LIGO gravitational wave detector highlighting that our calculation may allow for constraints to be placed on these theories. We model idealised data from the black hole merger signal GW150914 and perform a best fit analysis. The most likely value for the un-screened Brans-Dicke parameter is found to be ω = -1:42, implying on large scales gravity is very modified, incompatible with cosmological results.

The purpose of this thesis is to put forth and present a series of new applications of the gauge/string duality to areas of high energy physics and condensed matter physics. The contributions showcased in this thesis amount to the ever growing recollection of evidence that supports the duality, which has already become a broad and extensive field of its own. Most of the work contained in this thesis addresses the study of the quark gluon plasma, a state of matter that might allow to be approximated by simple gravitational descriptions and is, at the same time, accessible by experiment. This constitutes a great advantage, since it gives the possibility of testing the qualitative predictions that can be derived from the calculations in holography, like the ones presented in this thesis. One of them is that a heavy quark moving suficiently fast through a quark-gluon plasma may lose energy by Cherenkov-radiating mesons. Special emphasis is given to the fact that this effect takes place in all strongly coupled, large-Nc plasmas with a gravity dual. Phenomenological implications for heavy-ion collision experiments are also discussed. On the other hand, an extensive use is made of a IIB supergravity solution dual to a spatially anisotropic finite-temperature N = 4 super Yang-Mills plasma. Motivation comes from the fact that the quark gluon plasma created in heavy-ion collisions is anisotropic. The analysis focuses on three important observables of the plasma: Firstly, the drag force experienced by a massive quark propagating through the plasma is considered. The results show a generic misalignment of the gluon cloud trailing behind the quark, the quark velocity and the drag force itself whenever anisotropy is taken into account. Secondly, a study of the jet quenching parameter of the plasma is presented for arbitrary orientations and arbitrary values of the anisotropy. Perhaps surprisingly, the anisotropic value can be larger or smaller than the isotropic one, and moreover, this depends on whether the comparison is made at equal temperatures or at equal entropy densities. Finally, the screening length for quarkonium mesons in the anisotropic plasma is computed. The most important result is that not only can the temperature cause the dissociation of mesons, but anisotropy itself, even at zero temperature, may be responsible for it. Lastly, the duality is applied to the holographic description of anisotropic p-wave super- fluids, and a gravitational model is used to perform a complete analysis of their transport phenomena in the superfluid phase. The thermoelectric, piezoelectric and exoelectric effects are thoroughly studied. The results reproduce characteristic features of both superfluids and superconductors. In particular, the viscosities of the fluid deviate from the universal value, as is expected in an anisotropic condensed phase. An additional viscosity coeficient, associated to the difference in normal stresses and not previously considered in the holographic context, is also computed.
El propósito de esta tesis es presentar una serie de nuevas aplicaciones de la dualidad gauge/gravedad a áreas de la física de altas energías y de la materia condensada. La mencionada dualidad se ha convertido en un amplio y extenso campo, y las contribuciones resaltadas en esta tesis se unen a la creciente recopilación de evidencia que la apoya. La mayoría del trabajo realizado se refiere al estudio del plasma de quarks y gluones, un estado de la materia que podría permitir ser aproximado por simples descripciones gravitatorias y que es, al mismo tiempo, accesible experimentalmente. Esto daría la posibilidad de poner a prueba las predicciones cualitativas que se derivan de cálculos holográficos como los contenidos en esta tesis. Uno de ellos recoge la predicción de que un quark pesado moviéndose lo suficientemente rápido a través del plasma de quarks y gluones podría perder energía por radiación Cherenkov de mesones. Un énfasis especial se da al hecho de que este efecto tiene lugar en todos los plasmas fuertemente acoplados en el límite de gran N(c), siempre y cuando tengan un dual de gravedad. Por otra parte, se hace un extenso uso de una solución de supergravedad IIB dual a un plasma de N = 4 súper Yang-Mills anisotrópico a temperatura finita. La motivación viene del hecho de que el plasma de quarks y gluones creado en colisiones de iones pesados es anisotrópico. El análisis se centra en tres observables importantes del plasma: La fuerza de arrastre experimentada por un quark masivo que se propaga en el plasma, el parámetro de jet quenching para direcciones y valores de la anisotropía arbitrarios, y la longitud de apantallamiento de mesones de quarkonium en el plasma anisotrópico. Finalmente, se aplica la dualidad a la descripción holográfica de superufluídos de onda p. Se usa un modelo gravitatorio para realizar un análisis completo de sus fenómenos de transporte en la fase superufluídica. Los efectos termoeléctrico, piezoeléctrico y exoeléctrico se estudian en detalle. Los resultados reproducen características típicas tanto de superufluídos como de superconductores. También se calcula un coeficiente de viscosidad adicional, asociado a la diferencia de esfuerzos normales y no considerado previamente en el contexto holográfico.

Superstring theory is one current, promising attempt at unifying gravity with the other three known forces: the electromagnetic force, and the weak and strong nuclear forces. Though this is still a work in progress, much effort has been put forth toward this goal. A set of specific tools which are used are gauge/gravity dualities. This thesis consists of a specific implementation of gauge/gravity dualities to describe k-strings of strongly coupled gauge theories as objects dual to Dpbranes embedded in confining supergravity backgrounds from low energy superstring field theory. Along with superstring theory, k-strings are also commonly investigated with lattice gauge theory and Hamiltonian methods. A k$string is a colorless combination of quark-anti-quark source pairs, between which a color flux tube develops. The two most notable terms of the k-string energy are, for large quark anti-quark separation L, the tension term, proportional to L, and the Coulombic 1/L correction, known as the Luscher term. This thesis provides an overview of superstring theories and how gauge/gravity dualities emerge from them. It shows in detail how these dualities can be used for the specific problem of calculating the k-string energy in 2+1 and 3+1 space-time dimensions as the energy of Dp-branes in the dual gravitational theory. A detailed review of k-string tension calculations is given where good agreement is found with lattice gauge theory and Hamiltonian methods. In reviewing the k-string tension, we also touch on how different representations of k-strings can be described with Dp-branes through gauge/gravity dualities. The main result of this thesis is how the Luscher term is found to emerge from the energy calculation of Dp-branes. In 2+1 space-time dimensions, we have Luscher term data to compare with from lattice gauge theory, where we find good agreement.

La correspondance CFT (Anti-De Sitter) (AdS) / Théorie des champs conformes (CFT), également connue sous le nom de dualité holographique, constitue un lien remarquable entre la théorie des cordes (qui inclut la gravité) et les théories de jauge. Elle relie une CFT dans un espace-temps d-dimensionnel à une théorie de la gravité dans un espace-temps dimension supérieur, également appelé bloc. Ce dernier a une limite dans laquelle réside la théorie du champ conforme.Dans cette thèse, le sujet d'étude est la description holographique des flux de groupes de renormalisation (RG) des théories (de champ) sur les espaces-temps à symétrie maximale. Le cadre théorique que j'ai utilisé est la théorie d'Einstein-scalaire. L'inclusion du champ scalaire dynamique correspond à la rupture de l'invariance conforme aux limites. Dans ce travail, les limites et les tranches du bloc sont choisies pour être des espaces-temps à symétrie maximale et l'évolution des champs en bloc est étudiée. Il décrit les écoulements RG holographiques sur des variétés courbes. De plus, deux applications sont présentées dans cette thèse. La première application s'inscrit dans le contexte des théorèmes F et la seconde concerne un défaut incurvé dans les flux RG holographiques en masse.Les théorèmes F pour les théories de champs quantiques (QFT) définies dans des espaces-temps tridimensionnels exigent l'existence de fonctions dites F. Ce sont des fonctions décroissantes de façon monotone le long du flux RG. Dans ce travail, de nouvelles fonctions F pour les théories holographiques ont été découvertes. Elles sont construites à partir de l'action sur la parois d'une solution de flux holographique RG sur une sphère à 3-sphères. Ils permettent une interprétation entropique, fournissant ainsi un lien direct entre la formulation entropique du théorème F et sa définition en termes d’énergie libre.La deuxième application des flux RG holographiques explorée dans cette thèse se situe dans le contexte de modèles affichant un mécanisme d'auto-ajustement en tant que résolution proposée du problème de la constante cosmologique (CC). Dans ces modèles, notre univers à 4-dimensions est réalisé comme une brane intégrée dans un volume à 5-dimensions. Ce cadre permet des solutions où la géométrie de la brane est plate malgré la présence d'une énergie de vide non triviale sur son worldvolume. Ceci est appelé réglage automatique. De chaque côté de la brane, les solutions sont des flux RG holographiques. Le nouvel aspect introduit dans cette thèse consiste à utiliser les flux RG holographiques sur des variétés courbes, ce qui permet à son tour d’étudier des solutions à réglage automatique dans lesquelles la brane est également courbe
The Anti-de Sitter (AdS)/Conformal Field Theory (CFT) correspondence, also known as holographic duality, is a remarkable connection between string theory (which includes gravity) and gauge theories. It relates a CFT in a d-dimensional space-time to a gravity theory in higher dimensional space-time which is also referred to as the bulk. The latter has a boundary on which the conformal eld theory may be thought to reside. In this thesis, the subject of study is the holographic description of Renormalization Group (RG) fows of (field) theories on maximally symmetric space-times. The theoretical framework I used is Einstein-scalar theory. Inclusion of the dynamical scalar field corresponds to breaking boundary conformal invariance. In this work, both the boundary and bulk slices are chosen to be maximally symmetric space-times and the evolution of bulk fields is studied. It describes holographic RG flows on curved manifolds. Furthermore, two applications are presented in this thesis. The first application is in the context of F-theorems and the second is regarding a curved defect in the bulk holographic RG flows.F-theorems for Quantum Field Theories (QFT) defined on 3-dimensional space-times demand the existence of so-called F-functions. These are monotonically decreasing functions along the RG flow. In this work, new F-functions for holographic theories have been found which are constructed from the on-shell action of a holographic RG flow solution on a 3-sphere. They allow an entropic interpretation, therefore providing a direct connection between the entropic formulation of the F-theorem and its definition in terms of free energy. The second application of holographic RG flows explored in this thesis is in the context of models displaying a self-tuning mechanism as a proposed resolution of the cosmological constant (CC) problem. In these models, our 4-dimensional universe is realized as a brane embedded in a 5-dimensional bulk. This framework allows solutions where the brane geometry is flat despite of the presence of non-trivial vacuum energy on its worldvolume. This is referred to as self-tuning. On each side of the brane, the solutions are holographic RG flows. The new aspect introduced in this thesis is to use the holographic RG flows on curved manifolds, which in turn allows the study of self-tuning solutions where the brane is also curved

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.

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Doctorat en Sciences
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Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq
In this thesis we deal with G odel-type Universes in the context of modi ed gravity, in particular, Chern-Simons modi ed gravity and Brans-Dicke theory with cosmological constant (BD- ). The G odel-type metrics have been intensively discussed in the General Relativity (GR) over years. It is known that such a metrics present Closed Time-like Curves (CTC's), in other words, the G odel-type metrics are themselves an example of the causality violation. Our goal is verify the consistency of the G odel-type metrics within the Chern-Simons modi ed gravity in both: non-dynamical and dynamical formulations. In the non-dynamical framework, we show that is possible a vacuum solution in contrast to GR. Another essentially new result that we get is the presence of causal solutions for a well-motivated matter source, in general, the solutions have no analogue in GR. Moreover, the vacuum solution represents the limiting case separating the completely causal and non-causal regions, such a property re ects the topological features of the Chern-Simons theory. The primordial distinguishing feature between the Chern-Simons modi ed gravity and GR solutions is the presence of the breaking Lorentz symmetry. It turns out this breaking opens up a range of new solutions. We show that the non-trivial Chern-Simons solutions in the non-dynamical framework is accompanied by rst-order corrections of the Lorentz-violating parameter. Furthermore, in the dynamical framework the geometric parameters are also a ected by second-order corrections of the Lorentzviolating parameter. We also investigated the G odel-type metrics in BD- model. We obtain a vacuum solution which is completely causal, m2 = 4!2, where for ~! ! 1 one recovers the GR with a scalar eld and cosmological constant. It is worth calling attention to the role of the cosmological constant that is fundamental in this context.
Nesta tese tratamos os Universos tipo Code' no contexto da gravidade modificada, em particular, na gravidade modificada de Chern-Simons e na teoria de Brans-Dicke com constante cosmolOgica (BD-A). As metricas tipo Code' vem sendo intensamente discuti­das na Relatividade Geral (RG) ao longo dos anon. Sabe-se que tail metricas apresentam Curvas tipo Tempo Fechadas (CTC's), ou seja, as prOprias metricas tipo Code' sao um exemplo da violagao de causalidade. Nosso objetivo é verificar a consistencia das metricas do tipo Code' dentro da gravidade modificada de Chern-Simons em ambas as formula-goes: nao dinamica e dinamica. Na formulagao nao-dinamica, mostramos que é possivel uma solugao de vacuo diferentemente da RG. Outro resultado essencialmente novo que obtemos é a presenga de solugoes causais para uma fonte de materia bem motivada, em geral, as solugoes nao tem analog° na RG. Alem disso, a solugao de vacuo representa o caso limite que separa as regioes completamente causal e nao causal, tal propriedade re­flete as caracteristicas topolOgicas da teoria de Chern-Simons. A caracteristica que difere fundamentalmente as solugoes da gravidade modificada de Chern-Simons e as da RG é a presenga da quebra da simetria de Lorentz. Acontece que essa quebra abre um leque de novas solugoes. Mostramos que as solugoes nao triviais de Chern-Simons na formulagao nao dinamica sao acompanhadas por corregoes de primeira ordem do parametro de viola­gao de Lorentz. Alem disso, na formulagao dinamica os parametros geometricos tambem sao afetados por corregoes de segunda ordem do parametro de violagao de Lorentz. Investigamos tambem as metricas tipo Code' no modelo BD-A. Obtemos uma solugao de vacuo completamente causal, m2 = 4w2, onde para cD -+ oo recupera-se a GR com um campo escalar e constante cosmolOgica. Vale a pena chamar a atengao para o papel da constante cosmolOgica que é fundamental neste contexto.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES
In this cool thesis, we consider an approach to Brans-Dicke theory of gravity in which the scalar eld has a geometrical nature. By postulating the Palatini variation, we nd out that the role played by the scalar eld consists in turning the space-time geometry into a Weyl integrable manifold. This procedure leads to a scalar-tensor theory that di ers from the original Brans-Dicke theory in many aspects and presents some new features. We also consider the Weyl integrable geometry to investigate gravity in (2+1)-dimensions. We show that, in addition to leading to a Newtonian limit, WIST in (2+1) dimensions presents some interesting properties that are not shared by Einstein theory, such as geodesic deviation between particles in a dust distribution. Finally, taking advantage of the duality between the geometrical scalar-tensor theory and general relativity coupled with a massless scalar eld we study naked singularities and wormholes.
Esta tese trata de tópicos relacionados às teorias escalares-tensoriais e a geometria de Weyl integrável. Nossa abordagem será no sentido de indicar a geometria de Weyl integr ável como sendo um ambiente natural para a introdução de teorias escalares-tensorias. Nossa discussão será em torno da teoria de Brans-Dicke, considerada o protótipo das teorias escalares tensoriais, no entanto a discussão é facilmente estendida para essas versões mais gerais. Fazemos isso em dois momentos. Primeiro, indicando, no âmbito da teoria de Brans-Dicke, que na estrutura geométrica e de campos adotadas pela teoria existe uma relação estreita com a geometria de Weyl, inclusive associando o efeito descrito na literatura como "quinta força"(que violaria o princípio de equivalência) com o movimento geodésico da geometria de Weyl integrável, reformulando o postulado geodésico. E, num segundo momento, usando o método variacional de Palatini, acabamos por formular uma nova teoria escalar-tensorial, agora com ingredientes completamente geométricos, ambientada numa geometria de Weyl integrável. Estudamos ainda soluções no vazio do problema estático de uma distribuição de massa esfericamente simétrica, onde surgem objetos de interesse astrofísico como singularidades nuas e buracos de minhoca. Também formulamos a teoria conhecida por WIST (Weyl Integrable Spacetimes) em (2 + 1)D, o que resulta numa teoria consistente, não sofrendo das falhas associadas à teoria da relatividade geral nessa dimensionalidade

碩士
國立清華大學
物理學系
105
In this thesis, we reviewed the field of massive gravity. We present the development from linearized Fierz-Pauli theory to massive bi-gravity. Some feature on brane solutions in supergravity theory is also reviewed. We applied the method to search for the possibility of brane in massive bi-gravity theory.

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.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1991.
Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 99-100).

I examine the observational effects of a light scalar field with a scalar coupling to masses and a pseudoscalar coupling to light and particle spins. The pseudoscalar coupling to light induces a coupling to atomic spins both by inducing a coupling to particle spins directly, and by interactions with electromagnetic fields in the atom. Experiments measuring the interaction of spins to the gradient of the field are the only known way to measure the strength of the interaction with spins. However, limits on the interaction with light derived from these experiments are barely competitive with the separate astronomical limits on the scalar interaction and the interaction with light. Assuming a low mass of the field, as would be the case if the field acts as quintessence, the polarization rotation of the CMB provides a much tighter limit on the product of the pseudoscalar and scalar interaction strengths.

This dissertation is focused on three lines of work. In the first part, we consider aspects of holography and gauge/gravity duality in lower and higher dimensions. In particular, we study the duality for exact solutions localized on the Randal-Sundrum 2-branes. We also test if some holographic principles in general relativity can be generalized to include higher derivative theories of gravity; namely Lovelock gravity. In the second part we consider the role of pseudo Nambu-Goldstone bosons (pNGBs) in inflationary cosmology. Specifically, we construct an inflationary model using string theory axions, and use these pNGBs to produce the observed coherent magnetic field in the Universe. The third part of the thesis is devoted to the study of the phenomenology of emergent phenomena. We investigated whether one could test if diffeomorphism invariance, the sacred symmetry of general relativity, is emergent. We also construct a new minimal vectorial Standard Model, and argue that the absence of mirror particles predicted by this model can give us a hint about the fundamental nature of space.