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Costa, Filho Francisco Geraldo da. "Alguns Aspectos das Teorias de Gravidade Modificada." Universidade Federal da Paraíba, 2015. http://tede.biblioteca.ufpb.br:8080/handle/tede/9829.
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Previous issue date: 2015-02-27<br>Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq<br>Modifed theories of gravity has the objective to elucidate some open issues in the
context of general relativity. From this perspective many theories have been proposed
over the years. In this paper we deal with some of these theories and, for each of them,
we gave our contribution proposing new scenarios that showed promise. So in the
context of braneworld theory we held the first studies in three dimensional DGP theory,
with terms of induced gravity of the new massive gravity type. The study of the
propagators of disturbed theory showed unit propagation modes without the presence of
tachyons. As regards to the Horava-Lifshitz theory, we studied the structure of
membranes with scalar fields in 4+1 dimensions and the formation of black holes in 1+1
dimensions has been obtained for the first time. In the two previous cases we deal with
nonprojectable version of this theory. Have also studied braneworld models in a
bimetric theory where gravity is coupled to the scalar field that connects the two
metrics. Although the scalar field having a linear term kinetic the theory remained stable
and gravity localization was obtained. Finally, we apply the theory of gravitation with
nondynamical fields to a cosmological model and found that for a certain specific stage
of the Universe Expansion is possible to have a mechanism that generates a self tuning
of the cosmological constant problem.<br>Teorias de gravidade modificada tem como objetivo elucidar alguns problemas em
aberto no âmbito da Relatividade Geral. Dentro desta perspectiva muitas teorias foram
propostas ao longo dos anos. Neste trabalho abordamos algumas destas teorias e, para
cada uma delas, demos a nossa contribuição propondo novos cenários que se mostraram
promissores. Assim, no contexto das teorias de mundo-brana estudamos pela primeira
vez teorias do tipo DGP em 2+1 dimensões, com termos de gravidade induzida do tipo
nova gravidade massiva. O estudo dos propagadores da teoria perturbada mostrou a
propagação de modos unitários e sem a presença de táquions. No que diz respeito à
teoria de Horava-Lifshitz, estudamos a estrutura de branas com campos escalares em
4+1 dimensões e a formação de buracos em 1+1 foi obtida pela primeira vez. Nos dois
casos anteriores tratamos da versão não projetável desta teoria. Estudamos ainda
modelos de mundo-brana em uma teoria com bimétrica onde a gravidade se acopla ao
campo escalar que conecta as duas métricas. Apesar de o campo escalar possuir um
termo cinético linear a teoria se mostrou estável e localização da gravidade foi obtida.
Por fim, aplicamos a teoria da gravitação com campos não dinâmicos a um modelo
cosmológico e constatamos que para certa fase específica da expansão do Universo é
possível termos um mecanismo que gera um auto ajuste da constante cosmológica.
2
Lee, Seung Joo. "Braneworld inspired cosmology." Thesis, University of Sussex, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.426257.
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Whisker, Richard. "Braneworld black holes." Thesis, Durham University, 2006. http://etheses.dur.ac.uk/2323/.
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The braneworld paradigm provides an interesting framework within which to explore the possibility that our Universe lives in a fundamentally higher dimensional space- time. In this thesis we investigate black holes in the Randall-Sundrum braneworld scenario. We begin with an overview of extra-dimensional physics, from the original proposal of Kaluza and Klein up to the modern braneworld picture of extra dimensions. A detailed description of braneworld gravity is given, with particular emphasis on its compatibility with experimental tests of gravity. We then move on to a discussion of static, spherically symmetric braneworld black hole solutions. Assuming an equation of state for the "Weyl term", which encodes the effects of the extra dimension, we are able to classify the general behaviour of these solutions. We then use the strong field limit approach to investigate the gravitational lensing properties of some candidate braneworld black hole solutions. It is found that braneworld black holes could have significantly different observational signatures to the Schwarzschild black hole of standard general relativity. Rotating braneworld black hole solutions are also discussed, and we attempt to generate rotating solutions from known static solutions using the Newman-Janis complexification "trick".
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Kobayashi, Tsutomu. "Braneworld cosmological perturbations." 京都大学 (Kyoto University), 2006. http://hdl.handle.net/2433/144170.
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Kyoto University (京都大学)<br>0048<br>新制・課程博士<br>博士(理学)<br>甲第12087号<br>理博第2981号<br>新制||理||1445(附属図書館)<br>23923<br>UT51-2006-J82<br>京都大学大学院理学研究科物理学・宇宙物理学専攻<br>(主査)助教授 田中 貴浩, 教授 中村 卓史, 教授 畑 浩之<br>学位規則第4条第1項該当
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Vinet, Jérémie. "Aspects of braneworld cosmology." Thesis, McGill University, 2005. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=86059.
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What is essential is invisible to the eye. Antoine de Saint-Exupery<br>Of course, Saint-Exupery didn't have extra dimensions in mind when he wrote this famous line. Nevertheless, the recent realisation that standard model degrees of freedom can naturally be restricted to a submanifold embedded in a higher dimensional Universe means that an ingredient essential to our description of nature might quite literally be "invisible to the eye".<br>Exploring the consequences of such braneworld scenarios has occupied a large part of the theoretical physics community over the last seven years, and this thesis is a collection of contributions to this endeavour.<br>After reviewing the motivations for and early successes of braneworld scenarios, we examine rho2 corrections to the Hubble rate in the stabilized Randall-Sundrum I model, where the hierarchy problem is solved in a natural way, in order to ascertain whether such corrections might be of help in addressing some issues with inflation and baryogenesis. The three following chapters are concerned with six-dimensional models that have been advertised as possibly leading to a self-tuning solution to the cosmological constant problem. We examine this claim thoroughly, through the study of thick codimension-two braneworlds. This allows us to provide a generalization of the relationship between the deficit angle and the brane matter content. We also present the first derivation of the Friedmann equations on a codimension-two brane containing matter with an arbitrary equation of state, first in the context of Einstein-Hilbert gravity and then in six dimensional supergravity.
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Carvalho, C. "Cosmology of braneworld universes." Thesis, University of Cambridge, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.597344.
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The motivation of this study is the eventual application to calculating braneworld cosmological perturbations in order to determine observational signatures for the existence of extra dimensions. First, we construct five-dimensional bulk spacetime solutions, empty except for a negative cosmological constant, in the absence of any cosmological perturbations. Taking a higher-dimensional variant of Birkoff’s theorem, we find anti-de Sitter bulk solutions to the five-dimensional Einstein equations exhibiting three-dimensional spatial homogeneity and isotropy. We introduce branes as spacetime trajectories endowed with the same three-dimensional spatial symmetry as the bulk, hence capable of reproducing the observed homogeneity and isotropy of the universe. Second, we analyse the viability of a mechanism for the generation of a braneworld immersed in five-dimensional anti-de Sitter spacetime. An initial phase of de Sitter spacetime, which rapidly tends to an attractor vacuum state, is postulated. Through quantum tunnelling, bubbles of anti-de Sitter nucleate in the background de Sitter spacetime. From the collision of two such bubbles results a four-dimensional surface of constant negative spatial curvature where our four-dimensional universe will be localized. This mechanism has the advantage of explaining the bulk smoothness and horizon problems, of reproducing three-dimensional spatial homogeneity and isotropy, and also of giving rise to a warped geometry with the potential to explain the hierarchy problem. Third, we explore the nature of the brane-bulk interaction with a view towards computing the linearized cosmological perturbations for the models previously constructed. In particular, we focus on the study of the production and propagation of gravitational waves, since these are the only bulk degrees of freedom. We present the study of the quantum field theory of modes of a spring connected to a semi-infinite string in situations of increasing complexity, which exhibit all the qualitative features of the brane-bulk system except for gravitational gauge invariance. The production of gravitons is described by the motion of the spring, with the waves thus produced propagating through the string. A perturbative expansion of the brane propagator in five dimensions is contructed. Fourth, we consider the problem of gravitational gauge fixing for a brane moving on the boundary of the bulk spacetime solutions, its trajectory being determined by the evolution of its stress-energy content. The formulation of boundary conditions is essential for the complete definition of the problem of computing cosmological perturbations on a moving boundary. We derive the boundary conditions for linearized perturbations in a moving brane background spacetime and study the compatibility with the induced Lorentz gauge conditions. Fifth, we work out the effects on the graviton propagator due to the presence of simple forms of matter on the brane, namely a scalar field and a perfect fluid, which reproduce and inflationary and radiation/matter-dominated regimes from the four-dimensional perspective. We derive the boundary conditions modified by the presence of matter on the brane and expand perturbatively the brane and the bulk propagators.
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Padilla, Antonio. "Braneworld cosmology and holography." Thesis, Durham University, 2002. http://etheses.dur.ac.uk/4628/.
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This thesis is devoted to studying two important aspects of braneworld physics: their cosmology and their holography. We examine the Einstein equations induced on a general (n - 2)-brane of arbitrary tension, embedded in some n-dimensional bulk. The brane energy-momentum tensor enters these equations both linearly and quadratically. From the point of view of a homogeneous and isotropic brane we see quadratic deviations from the FRW equations of the standard cosmology. There is also a contribution from a bulk Weyl tensor. We study this in detail when the bulk is AdS-Schwarzschild or Reissner-Nordstrom AdS. This contribution can be understood holographically. For the AdS-Schwarzschild case, we show that the geometry on a brane near the AdS boundary is just that of a radiation dominated FRW universe. The radiation comes from a field theory that is dual to the AdS bulk. We also develop a new approach which allows us to consider branes that are not near the AdS boundary. This time the dual field theory contributes quadratic energy density/pressure terms to the FRW equations. Remarkably, these take exactly the same form as for additional matter placed on the brane by hand, with no bulk Weyl tensor. We also derive the general equations of motion for a braneworld containing a domain wall. For the critical brane, the induced geometry is identical to that of a vacuum domain wall in (n-l)-dimensional Einstein gravity. We develop the tools to construct a nested Randall-Sundrum scenario whereby we have a "critical" domain wall living on an anti-de Sitter brane. We also show how to construct instantons on the brane, and calculate the probability of false vacuum decay.
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Leeper, Emily. "Dynamics of cosmological braneworld models." Thesis, University of Portsmouth, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.425773.
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Gumjudpai, Burin. "Braneworld effects on cosmological dynamics." Thesis, University of Portsmouth, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.396334.
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Rhodes, Christophe Sebastian. "Cosmological observations in braneworld models." Thesis, University of Cambridge, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.615727.
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Webster, Samuel Luke. "Effective theories for braneworld cosmology." Thesis, University of Cambridge, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.614226.
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Crampton, Benedict. "Hyperbolic braneworld backgrounds in supergravity." Thesis, Imperial College London, 2013. http://hdl.handle.net/10044/1/27229.
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The manifolds Hp,q [Symbol appears here. To view, please open pdf attachment] are a family of non-compact hyperboloids carrying inhomogeneous Euclidean metrics. In supergravity they appear as an interesting class of dimensional reductions, related to the well known sphere reductions by a simple analytic continuation. The spectrum of lower dimensional modes in these backgrounds is still poorly understood. In this thesis, we construct the complete Pauli reduction of type IIA supergravity on H2,2 [Symbol appears here. To view, please open pdf attachment] . We carefully analyse the spectrum of gravitational waves in the resulting Salam-Sezgin background, and identify the boundary conditions needed to render these modes normalisable. We give these boundary conditions a codimension-2 braneworld interpretation. We then exhibit a supersymmetric braneworld geometry based on the NS5-brane. In the remainder of this thesis we apply holographic methods to the problem of the fractionalisation transition in condensed matter theory. We exhibit a phase transition between a superconducting and a fractionalised phase in a bottom-up Einstein-Maxwell-Dilaton theory, and discuss the importance of entropy scaling in achieving this.
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Lehners, Jean-Luc. "Braneworlds from supergravity." Thesis, Imperial College London, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.420312.
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Tuma, Niemi Toivo. "When Braneworlds Collide." Thesis, Uppsala universitet, Teoretisk fysik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-448725.
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This project is an investigation of a cosmological model consisting of a five dimensional AdS-vacuum with a flux. By discharges in the flux, four dimensional bubbles can nucleate in the vacuum and collide with each other while expanding. Our observable universe is considered to be localized on the membrane of such a bubble. The main purpose of the model was to find a possible explanation for dark energy and inflation. We compute the Friedmann equation for an expanding bubble, as well as analytical expressions for the two slow roll parameters ε and η related to slow roll inflation. We also show that there exists a set of parameters of the model where both slow roll parameters are small enough in order for inflation to last for at least 60 Hubble times. However, our model doesn’t survive all consistency checks with today’s observations. We conclude that even if the resulting slow roll parameters look promising, one has to either look harder for a set of ”good” fundamental parameters of the model, or further develop it to have a chance of surviving all consistency checks.<br>Populärvetenskaplig sammanfattning: Det här projektet undersöker en kosmologisk modell bestående av ett femdimensionellt vakuum med negativ rumtidkrökning. I vakuumet finns ett elektriskt fält, som i högre dimensioner än fyra kallas flux (flöde). Urladdningar i detta flux gör det möjligt för fyrdimensionella bubblor att uppstå i vakuumet. Dessa vakuumbubblor expanderar snabbt och kommer så småningom att kollidera med varandra. Tanken är att vårt fyrdimensionella observerbara universum utgör en del av membranet på en av dessa expanderande vakuumbubblor. De andra vakuumbubblorna kan - om man vill - betraktas som parallella universum. Målet med detta projekt har varit att hitta en möjlig model för kosmisk inflation - epoken i vårt universums ungdom då rummet expanderade enormt snabbt under en väldigt kort tidsperiod. Inflationen i vår modell äger rum när vakuumbubblan för vårt universum kolliderar med andra vakuumbubblor. Vi lyckades visa att den här modellen kan ge upphov till inflation som varar tillräckligt länge för att det ska stämma överens med dagens observationer av vårt observerbara universum. Dock förutspår modellen även andra saker som inte stämmer överens med observationerna. Vår slutsats är att modellen ser lovande ut, men att man antingen behöver undersöka den noggrannare eller utveckla den på något sätt, om den ska ha en chans att stämma överens med universumet vi observerar.<br><p>Presentationen skedde över videolänk på grund av Covid-19.</p>
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Hawkins, Rachael Mary. "Scalar field Braneworld and inflationary cosmologies." Thesis, Queen Mary, University of London, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.414462.
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Mistry, Bina. "Braneworld black holes and black strings." Thesis, Durham University, 2008. http://etheses.dur.ac.uk/2242/.
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This thesis involves the study of strong and weak gravity phenomenology within the braneworld paradigm. We begin with a general overview of the hypothesised concept of extra spatial dimensions and explain why they are so interesting. Turning next to the topic of classical four-dimensional black holes, we discuss their formation via gravitational collapse and indicate some of the strong observational evidence of their existence. We then merge the two independent theories of extra dimensions and black holes together to form braneworld black holes. Focusing our attention on two distinct braneworld scenarios, we examine the effects produced from either strong or weak gravity. The prospect of obtaining experimental verification of the existence of additional spacelike dimensions in the upcoming ground-based accelerators, makes the theoretical research of braneworld gravity within this thesis even more enticing. We start with a non-perturbative approach to look for exact, spherically symmetric star or black hole solutions on a Randall-Sundrum brane from the perspective of the five-dimensional spacetime. By fixing the background, we explore the permissible braneworld trajectories within it that correspond to a braneworld observer, the solutions of the brane Tolmann-Oppenheimer-Volkoff equations. A variety of static gravitating matter sources on the brane are obtained in a range of different backgrounds. Our final aim is a consistent brane embedding in a Schwarzschild- Anti de Sitter spacetime as these solutions are potential candidates for brane stars or black holes. The weak and dominant energy conditions determine the physically sensible solutions which have the interpretation of braneworld stars. We then study time-dependent trajectories as a possible description of time-dependent braneworld black holes. This work is then generalised by relaxing the simplifying assumption of Z(_2)-symmetry, previously imposed around the brane. Non-Z(_2) symmetric spacetimes are applicable in processes which concern only one side of the brane, for example black hole recoil or the emission of Hawking radiation. We determine that a subset of the allowed brane trajectories in an asymmetric background are exactly the same as the Z(_2)-symmetric case. Next, we explore perturbative gravity in the Hofava-Witten model of heterotic M-theory. The study of scalar and gravitational fluctuations determines that the radion mode is coupled to the bulk scalar field, indicating only one single degree of freedom. Our analysis also determines the instability of a black string. We then compute the complete mass spectrum of the graviton mode. Using the five-dimensional gravitational physics, we determine what the gravitational interaction an observer on the braneworld would perceive. This analysis involves the computation of the Newtonian potential between two test masses on the visible brane, together with the four-dimensional tensor structure of the massless graviton propagator. Finally, as an application to the earlier work, we comment on work which is in progress: the study of possible brane black hole solutions in low energy heterotic M-theory.
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Palma, Gonzalo Alejandro. "Bulk scalar fields in braneworld models." Thesis, University of Cambridge, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.614285.
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Descheneau, Julie. "A review of six-dimensional braneworld solutions /." Thesis, McGill University, 2003. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=80251.
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In the last years, brane world scenarios have been studied extensively, but most of these studies have been done in the case of five-dimensional spacetime. It is therefore of interest to investigate which of the particular features observed are proper to one extra dimension and which are generic to any number of dimensions. In this thesis, I present an overview of models and solutions to Einstein's equations for six-dimensional brane world scenarios. Solutions for a simple setup with cylindrically symmetric bulk centered about a three-brane are derived and classified. There are two main kinds of topology: either solutions are compactified in a spherical topology, closed up by another three-brane, or they have a disc topology, which must be terminated by a four-brane. One of the particular features of codimension-two branes is demonstrated, namely that their tension, or vacuum energy, induces a deficit angle in the bulk. Solutions for different arrangements of codimension-one and codimension-two branes are also reviewed. Although the review focuses on topological and cosmological properties of the solutions, models using a field theoretical approach to the brane-world scenario, i.e. considering the brane as a topological defect arising from higher dimensional fields, are also considered.
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De, Rham Claudia Anna. "Braneworld cosmology beyond the low-energy limit." Thesis, University of Cambridge, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.615190.
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Wong, Ki-Cheong, and 王祺昌. "Applications of braneworld models to the theory of gravitation." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2012. http://hub.hku.hk/bib/B48329538.
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I have presented an evolving wormhole solution in braneworld model. Moreover I have shown that there are observational signatures for using braneworld to solve dark matter problem.
Braneworld assumed that four dimensional spacetime embedded into five dimensional bulk. Gravity is a five dimensional interaction and the usual four dimensional description is reproduced by geometric projection. It predicts correction terms to the Einstein equation, for instance, the higher dimensional Weyl curvature projected on the brane.
This projected Weyl curvature could make braneworld wormhole satisfies the Null Energy Condition (NEC), which is impossible in general relativity. We considered inflating braneworld wormhole that enlarge with the Universe, the wormhole is supported by the Weyl curvature so that it satisfies NEC. We demonstrated how this wormhole embedded into a five dimensional bulk and studied how it evolve with our Universe. The result is that inflating wormhole satisfying general initial condition will collapse into black hole when the scalar field oscillates.
In addition, the projected Weyl curvature introduces a new source of gravity. This Weyl fluid of geometrical origin (reducing in the spherically symmetric, static configuration to a dark radiation and dark pressure) modifies space-time geometry around galaxies and has been used to explain the flatness of galactic rotation curves. Independent observations for discerning between the Weyl fluid and other dark matter models are necessary. Gravitational lensing could provide such a test. Therefore we study null geodesics and weak gravitational lensing in
the dark radiation dominated region of galaxies in a class of spherically symmetric braneworld metrics. We find that the lensing profile in the braneworld scenario is distinguishable from dark matter lensing, despite both the braneworld scenario and dark matter models can fit the rotation curve data. In particular, in the asymptotic regions light deflection is 18% enhanced as compared to dark matter halo predictions. For a linear equation of state of the Weyl fluid we further find a critical radius, below which braneworld effects reduce, while above it they amplify light deflection. This is in contrast to any dark matter model, which
always increases the deflection angle.<br>published_or_final_version<br>Physics<br>Doctoral<br>Doctor of Philosophy
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Creek, Simon. "Higher-dimensional black holes : braneworld stars and Hawking radiation." Thesis, Durham University, 2007. http://etheses.dur.ac.uk/2876/.
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In this thesis two aspects of braneworld models are studied. A new attempt at finding the metric of a braneworld black hole within the second Randall-Sundrum model is explored. Branes containing distributions of perfect fluid are embedded in a variety of 5-dimensional 5O(4)-symmetric bulk spacetimes so that the Israel junction conditions are satisfied. A particular class of time-dependent embeddings are studied and shown to be unable to describe the braneworld black hole. Static trajectories are then investigated in five-dimensional anti-de Sitter and Schwarzschild backgrounds. These reveal a wide variety of permissible trajectories which are classified according to their energy-momentum profiles. The static embedding of branes in a Schwarzschild-anti-de Sitter spacetime is then explored, revealing objects with possible interpretation as "braneworld stars”. The evaporation of higher-dimensional rotating black holes, both on the brane and in the bulk is studied from an analytical perspective. A matching technique is employed to derive the solution for the radial component of the fields of scalars, fermions and gauge bosons propagating in the brane-induced line-element of a higher-dimensional rotating black hole. These solutions are used to calculate Hawking radiation spectra from a black hole in the spin-down phase of its lifetime within the Arkani-Hamed-Dimopoulos-Dvali model. The same method is used to calculate the emission of scalar fields into the bulk spacetime of a higher-dimensional rotating, black hole and a comparison is made between brane and bulk emission rates. Finally the matching technique is applied to the problem of graviton emission in the bulk from a higher-dimensional Schwarzschild black hole.
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PeÌrez, Ena Erandy RamiÌrez. "Inflationary dynamics and pertubations in standard and braneworld cosmologies." Thesis, University of Sussex, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.424186.
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Wang, Daoyan. "Gravitational collapse and black hole formation in a braneworld." Thesis, University of British Columbia, 2015. http://hdl.handle.net/2429/52797.
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In this thesis we present the first numerical study of gravitational collapse in braneworld within the framework of the single brane model by Randall-Sundrum (RSII). We directly show that the evolutions of sufficiently strong initial data configurations result in black holes (BHs) with finite extension into the bulk. The extension changes from sphere to pancake (or cigar, as seen from a different perspective) as the size of BH increases. We find preliminary evidences that BHs of the same size generated from distinct initial data profiles are geometrically indistinguishable. As such, a no-hair theorem of BH (uniqueness of BH solution) is suggested to hold in the RSII spacetimes studied in this thesis—these spacetimes are axisymmetric without angular momentum and non-gravitational charges. In particular, the BHs we obtained as the results of the dynamical system, are consistent with the ones previously obtained from a static vacuum system by Figueras and Wiseman. We also obtained some results in closed form without numerical computation such as the equality of ADM mass of the brane with the total mass of the braneworld.
The calculation within the braneworld requires advances in the formalism of numerical relativity (NR). The regularity problem in previous numerical calculations in axisymmetric (and spherically symmetric) spacetimes, is actually associated with neither coordinate systems nor the machine pre- cision. The numerical calculation is regular in any coordinates, provided the fundamental variables (used in numerical calculations) are regular, and their asymptotic behaviours at the vicinity of the axis (or origin) are compatible with the finite difference scheme. The generalized harmonic (GH) formalism and the BSSN formalism for general relativity are developed to make them suitable for calculations in non-Cartesian coordinates under non-flat background. A conformal function of the metric is included into the GH formalism to simulate the braneworld.<br>Science, Faculty of<br>Physics and Astronomy, Department of<br>Graduate
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Chen, Fang. "Friedman equation in codimension-two braneworlds." Thesis, McGill University, 2008. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=18685.
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We study the expansion of the universe on a deSitter 3-brane in a warped codimension-two brane model. We use analytical and numerical methods to solve the jump conditions and quantify the deviations of the Friedmann equation from its standard form. The radion must be stabilized in this model, and it is shown that the magnitude of the deviations is controlled by the radion mass, though in a quantitatively different way from codimension-one brane models. We also examine the effect of the modified expansion rate on inflation driven by fields on the brane.<br>Nous étudions l'expansion de l'univers sur un desitter 3-brane dans un modèle déformé de brane de dimension 2. Nous employons des méthodes analytiques et numériques pour résoudre les conditions de saut et pour mesurer les déviations de l'équation de Friedmann a partir de son format standard. Le radion doit être stabilisé dans ce modèle, et on démontre que l'importance des déviations est commandée par la masse de radion, cependant de faéon quantitativement différente a partir de modèles de brane de dimension 1. Nous examinons également l'effet du taux modifié d'expansion sur l'inflation conduite par des champs sur le brane.
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Huston, Ian. "Constraining inflationary scenarios with braneworld models and second order cosmological perturbations." Thesis, Queen Mary, University of London, 2010. http://qmro.qmul.ac.uk/xmlui/handle/123456789/584.
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Inflationary cosmology is the leading explanation of the very early universe. Many diff erent models of inflation have been constructed which fit current observational data. In this work theoretical and numerical methods for constraining the parameter space of a wide class of such models are described. First, string-theoretic models with large non-Gaussian signatures are investigated. An upper bound is placed on the amplitude of primordial gravitational waves produced by ultra-violet Dirac-Born-Infeld inflation. In all but the most finely tuned cases, this bound is incompatible with a lower bound derived for inflationary models which exhibit a red spectrum and detectable non-Gaussianity. By analysing general non-canonical actions, a class of models is found which can evade the upper bound when the phase speed of perturbations is small. The multicoincident brane scenario with a finite number of branes is one such model. For models with a potentially observable gravitational wave spectrum the number of coincident branes is shown to take only small values. The second method of constraining inflationary models is the numerical calculation of second order perturbations for a general class of single fi eld models. The Klein-Gordon equation at second order, written in terms of scalar field variations only, is numerically solved. The slow roll version of the second order source term is used and the method is shown to be extendable to the full equation. This procedure allows the evolution of second order perturbations in general and the calculation of the non-Gaussianity parameter in cases where there is no analytical solution available.
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Aghababaie, Yashar. "Six-dimensional supergravity braneworlds and the cosmological constant." Thesis, McGill University, 2005. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=100310.
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We review the lore of effective field theories as a background to hierarchy problems in general and the cosmological constant problem in particular. We outline some of the attempted four-dimensional solutions to the cosmological con stant problem and conclude that ones based upon the usual assumptions of four-dimensiona lfield theory typically do not work. We argue that one way to relax the assumptions is to seek solutions to the cosmological constant problem which rely on the presence of extra dimensions. We explicitly exhibit that standard compactification techniques fail to solve the cosmological constant problem because they reduce the problem to a four-dimensional one.<br>We argue that brave-world models may be helpful in solving the cosmological constant problem because standard model loops contribute to the tension and not to the vacuum energy directly, and can fulfill our stated aim of constructing a model which uses the extra dimensions to mitigate the cosmological constant problem. We identify necessary (not sufficient) properties a theory must possess to successfully use this observation. These properties are: a scaling symmetry encoded in a dilaton-like scalar, and bulk supersymmetry.<br>We therefore investigate supersymmetric six-dimensional brave-world models. Our models are imbedded within a 6D supergravity that has many of the features of realistic string models. We explicitly show that the compactification of the 6D theory has many of the same features as string compactifications, including flat four-dimensional space, chiral fermions, rnoduli, moduli-stabilisation using fluxes, and gluino condensation. We show that by calculating the non-perturbative correction to the superpotential and loop-corrections to the Kahler function that a meta-stable deSitter vacuum can be found. The vacuum energy can be tuned to be ∼ 10-6 M4Planck .<br>We find that all solutions of the supergravity equations of motion, under a symmetry ansatz, have flat braves. This implies that this property is independent of some of the details of the braves, such as their tensions. The source of the branes' flatness is the required classical scaling symmetry of the action.<br>We consider whether this class of models may provide a solution to the cosmological constant problem within the large extra dimensions scenario, in which the radius r ∼ 0.1mm, and in which the standard-model fields are trapped on a 3-brave. We conclude that it may be possible to produce naturally a cosmological constant that is of order r -4 ∼ (10-3eV)4 due to loops because the supersymmetry-breaking scale in the bulk is MSUSY ∼ r-1; although there remains a great deal of work to be done. We comment on recent extensions to cosmological backgrounds.<br>Further work within these models is outlined, including higher-dimensional models, use of effective field-theory techniques in theories with sharp boundaries, and the treatment of quantum corrections.
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Yamashita, Yasuho. "Embedding Ghost-free Bigravity into Higher-Dimensional Gravity." 京都大学 (Kyoto University), 2017. http://hdl.handle.net/2433/225402.
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Bostock, Paul B. "Geometry of black holes and braneworlds in higher dimensions." Thesis, Durham University, 2004. http://etheses.dur.ac.uk/3115/.
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This tliesis first discusses braneworld models, we explain how the bulk geometry in codimension 2 scenarios restricts braneworld fields in a way inconsistent with observation. We then show how generalising Einstein's equations to include Gauss-Bonnet terms avoids this problem and as an example we successfully reproduce the Priedmann-Robertson-Walker cosmology familiar in Einstein gravity. The work on braneworlds concludes with a detailed perturbation analysis of a simple conical space-time in Gauss-Bonnet gravity, non-trivially we find the standard four-dimensional Lichnerowicz equation on the brane even though the calculation is performed in six dimensions. Next, motivated by the microscopic description of black hole thermodynamics, we discuss Gubser and Mitra's conjectured relationship between classical and thermodynamic stability including a review of numerical and theoretical evidence for it. We then give an argument using a recently discovered ansatz for non-uniform smeared p-brane solutions that the conjecture fails in the generality in which it is proposed. The thesis emphasises the underlying relationship between world volume field theory and bulk gravity from a geometrical point of view throughout.
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Leong, Bernard Chung Wei. "Spin-torsion, braneworlds and changing symmetry in the Universe." Thesis, University of Cambridge, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.619661.
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Hamilton, Keith M. "eâºe⻠→ μâºÎ¼â» in the Standard Model and Braneworld." Thesis, University of Oxford, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.403737.
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SAHABANDU, INOKA C. "PERTURBATIVE METHODS OF SOLUTION FOR BLACK HOLES AND BLACK STRINGS IN BRANEWORLD MODELS." University of Cincinnati / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1184648511.
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Wong, Ki-cheong, and 王祺昌. "Inflation and late time acceleration of the universe by variable Branetension on Braneworld model." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2009. http://hub.hku.hk/bib/B43224015.
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Wong, Ki-cheong. "Inflation and late time acceleration of the universe by variable Brane tension on Braneworld model." Click to view the E-thesis via HKUTO, 2009. http://sunzi.lib.hku.hk/hkuto/record/B43224015.
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Dantas, Davi Monteiro. "Localização de modos fermiônicos em uma geometria de seis dimensões do tipo Conifold." reponame:Repositório Institucional da UFC, 2012. http://www.repositorio.ufc.br/handle/riufc/13704.
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DANTAS, Davi Monteiro. Localização de modos fermiônicos em uma geometria de seis dimensões do tipo Conifold. 2012. 83 f. Dissertação (Mestrado em Física) - Programa de Pós-Graduação em Física, Departamento de Física, Centro de Ciências, Universidade Federal do Ceará, Fortaleza, 2012.<br>Submitted by Edvander Pires (edvanderpires@gmail.com) on 2015-10-21T21:39:04Z
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Previous issue date: 2012<br>One way to solve the hierarchy problem and therefore unify the fundamental forces is to assume, under the theoretical point of view, that our four-dimensional space (Brane) is housed in a space of higher dimensionality (Bulk). We call all that extra dimension which is not present in our Brana. The idea of extra dimensions to include unification of fundamental forces date from the 30s of last century, with the innovative proposal of Kaluza and Klein, and has been evolving ever since its formulation. Thus, other innovative proposals like that of the work of Randall and Sundrum have created new possibilities for the study, although it is curious that cite not have any experimental evidence to date that these dimensions exist. Fundamental fermionic particles have as one of its interesting properties the existence of left and right chiral modes, this information widely studied in the Standard Model and Supersymmetry in the call. In this article we treat on the location of the chiral modes, massless and massive, the fermionic fields of spin 1/2 in a six-dimensional space of type Conifold solved. This space has an adjustable parameter which allows to recover the geometry of other works of literature. Beyond this generalization was possible to find other interesting results as the thickening of the Brana and smoothing the model studied in 6D. Looking at work that the ratio of chiral modes is strictly dependent on the choice of coupling fields used. For free fermions chiral modes are identical. Regarding the location of Massive modes, we find that by rewriting the Dirac equation, obtained from our action, in a way kind of Schrödinger equation, we find a term potential. We found that when using the factors derived from the sixth dimension as a term coupling, we obtain results similar to a Yukawa coupling in five dimensions.<br>Uma das formas de resolver o Problema de Hierarquia e por consequência unificar as forças fundamentais da natureza é assumir, sob o ponto de vista teórico, que nosso espaço quadrimensional (brana) está inserido em um espaço de dimensionalidade maior (bulk). Chamamos de dimensão extra toda aquela que não está presente em nossa brana. A idéia de incluir dimensões extras para unificação de forças fundamentais data dos anos 30 do século passado, com a inovadora proposta de Kaluza e Klein, e vem evoluindo sua formulação desde então. Assim, outras propostas inovadoras como aquela do trabalho de Randall e Sundrum, criaram novas possibilidades para o estudo, embora seja interessante citar que não possuímos nenhuma evidência experimental até o presente momento de que tais dimensões existam. Partículas fundamentais fermiônicas têm como uma de suas propriedades interessantes a existência dos modos quirais direito e esquerdo, informação esta bastante estudada no Modelo Padrão assim como em Supersimetria. Nesse trabalho tratamos sobre a localização dos modos quirais, sem massa e massivo, de campos fermiônicos de spin 1/2 em uma espaço de seis dimensões do tipo Conifold Resolvido. Este espaço possui um parâmetro regulável, o qual permite obter geometrias de outros trabalhos da literatura como casos particulares. Além desta generalização, foi possível encontrar outros resultados interessantes como o espessamento da brana e suavização do modelo estudado em 6D. Observaremos também que a relação dos modos quirais é estritamente dependente da escolha do acoplamento de campos utilizado. Para férmions livres, os modos quirais serão idênticos. Quanto à localização de Modos Massivos, verificaremos que ao reescrever a equação de Dirac, obtida a partir de nossa ação, em uma forma do tipo equação de Schrödinger, encontraremos um termo de potencial. Estudaremos que ao se utilizar os fatores derivados da sexta dimensão como um termo de acoplamento, obteremos resultado semelhante ao de um acoplamento Yukawa em cinco dimensões.
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Niedermann, Florian [Verfasser], and Stefan [Akademischer Betreuer] Hofmann. "Natural braneworlds in six dimensions and the cosmological constant problem / Florian Niedermann. Betreuer: Stefan Hofmann." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2016. http://d-nb.info/1102157309/34.
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Jacobs, David M. "Casimir Localization." Case Western Reserve University School of Graduate Studies / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=case1396608069.
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Oliveira, Jéferson de. "Perturbação de spin zero no espaço-tempo de Kerr-Randall-Sundrum." Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-22052009-192805/.
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Esta dissertação visa realizar um estudo acerca dos modelos de mundo brana no contexto proposto por Randall e Sundrum. O trabalho focaliza as perturbações de spin 0 no espaço-tempo de Kerr tomado como um mundo brana 4-dimensional. Para isso apresentamos os principais aspectos da Relatividade Geral de Einstein, bem como perturbações em métricas que descrevem buracos negros. Fizemos uma revisão dos modelos de Randall-Sundrum, suas motivações e tentativas de descrever buracos negros na brana. Por m a perturbação escalar da corda negra em rotação (Kerr-Randall-Sundrum) e o fenômeno de super-radiação são analisados.<br>This dissertation aims at studying the braneworld models in the context proposed by Randall and Sundrum. The focus is on the spin-0 perturbations in the Kerr space-time as a 4- dimensional braneworld. The work deals the main aspects of Einstein General Relativity as well as perturbations of black holes metrics. We also review the Randall-Sundrum models and their motivations and attempts to describe braneworld black holes. In the end the Kerr-Randall-Sundrum black string scalar perturbation and superradiance are obtained.
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Marques, Araújo Marques. "Soluções localizadas em diversas dimensões." Universidade Federal da Paraíba, 2015. http://tede.biblioteca.ufpb.br:8080/handle/tede/8005.
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Previous issue date: 2015-02-25<br>Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq<br>This dissertation deals with localized solutions in several dimensions. Initially, we review
some topics in classical theory of fields by using scalar fields both in flat and curved
spacetime. Here they are: kinks, lumps, vortices, monopoles, dyons, cosmology with
scalar fields and branes modeled by scalar fields. After this, we present some original
results. Firstly, by introducing a real or integer parameter in the models, we study a
way to go from kinks to compactons in models with standard dynamics and show how the
procedure works in the braneworld scenario. Finally, by using the deformation method, we
present new models that support compact structures and then study their linear stability.<br>Esta dissertação lida com soluções localizadas em diversas dimensões. Inicialmente, fazemos
uma revisão de alguns tópicos em teoria clássica de campos usando campos escalares
tanto no espaço plano como no espaço curvo. São eles: kinks, lumps, vórtices, monopolos,
dyons, cosmologia com campos escalares e branas modeladas por campos escalares. A seguir
apresentamos alguns resultados originais. Primeiramente, introduzindo nos modelos
um parâmetro que pode ser real ou inteiro, estudamos uma maneira de ir de kinks para
compactons em modelos com dinâmica padrão e mostramos como o procedimento funciona
no cenário de mundo brana. Por fim, usando o método da deformação, apresentamos
novos modelos que suportam estruturas compactas e estudamos sua estabilidade linear.
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Sousa, Junior Altemar Lobão de. "Teorias de campos com dinâmica generalizada." Universidade Federal da Paraíba, 2014. http://tede.biblioteca.ufpb.br:8080/handle/tede/5751.
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Previous issue date: 2014-07-17<br>Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES<br>This thesis discusses the mathematical formalism to obtain solutions of topological defects
in theories of field with modified dynamics. We will check that defect solutions, in
generalized theories, can be obtained so much in 4-dimensional spacetime of Minkowski
as in a spacetime with extra dimension of the deformed geometry. Will be shown both
in four-dimensional spacetime as in spacetime as an extra dimension, that the solution
characteristics, such as energy density and perturbative spectrum, which appears in the
theories with modified dynamic may be profoundly diferent from those that arise in the
theories with dynamics standard. We also find the necessary conditions for that the energy
density and the perturbative spectrum remain unchanged compared to that obtained in a
theory with dynamics standard. In the case of a defect in a spacetime of extra dimension
with warped geometry, we use models with generalized dynamic to describe the so-called
braneworld scenarios. The study of brane will be divided into two parts: in the first the
modification will be performed in the dynamics of the Lagrangian density and the second
will be an analogy to called gravity F(R), being added new terms dependent of scalar
curvature in the action of Einstein-Hilbert.<br>Esta tese discute o formalismo matemático para se obter soluções de defeitos topológicos
em teorias de campo com dinâmica modificada. Verificaremos que soluções de defeito,
em teorias generalizadas, podem ser obtidas tanto no espaço tempo quadridimensional
de Minkowski como em um espaço tempo de dimensão extra com geometria deformada.
Será mostrado, tanto no espaço tempo quadridimensional, quanto no espaço tempo de
dimensão extra, que as características da solução, como densidade de energia e espectro
perturbativo, que surge nas teorias com dinâmica modificada, podem ser profundamente
distintas das que surgem nas teorias com dinâmica padrão. Encontraremos também quais
as condições necessárias para que a densidade de energia e espectro perturbativo permaneçam inalterados em relação ao obtido em uma teoria com dinâmica padrão. Em se
tratando de defeito em um espaço tempo de dimensão extra com geometria deformada,
utilizaremos modelos com dinâmica generalizada para descrever os chamados cenários de
mundo brana. O estudo de brana será dividido em duas partes: na primeira será realizada
uma modificação na dinâmica da densidade de lagrangiana e na segunda será feito uma
analogia às chamadas gravidade F(R), sendo adicionado novos termos dependentes do
escalar de curvatura à ação Einstein-Hilbert.
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Dantas, Davi Monteiro. "LocalizaÃÃo de modos fermiÃnicos em uma geometria de seis dimensÃes do tipo Conifold." Universidade Federal do CearÃ, 2012. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=8877.
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Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico<br>Uma das formas de resolver o Problema de Hierarquia e por consequÃncia unificar as forÃas fundamentais da natureza à assumir, sob o ponto de vista teÃrico, que nosso espaÃo quadrimensional (brana) està inserido em um espaÃo de dimensionalidade maior (bulk). Chamamos de dimensÃo extra toda aquela que nÃo està presente em nossa brana. A idÃia de incluir dimensÃes extras para unificaÃÃo de forÃas fundamentais data dos anos 30 do sÃculo passado, com a inovadora proposta de Kaluza e Klein, e vem evoluindo sua formulaÃÃo desde entÃo. Assim, outras propostas inovadoras como aquela do trabalho de Randall e Sundrum, criaram novas possibilidades para o estudo, embora seja interessante citar que nÃo possuÃmos nenhuma evidÃncia experimental atà o presente momento de que tais dimensÃes existam. PartÃculas fundamentais fermiÃnicas tÃm como uma de suas propriedades interessantes a existÃncia dos modos quirais direito e esquerdo, informaÃÃo esta bastante estudada no Modelo PadrÃo assim como em Supersimetria. Nesse trabalho tratamos sobre a localizaÃÃo dos modos quirais, sem massa e massivo, de campos fermiÃnicos de spin 1/2 em uma espaÃo de seis dimensÃes do tipo Conifold Resolvido. Este espaÃo possui um parÃmetro regulÃvel, o qual permite obter geometrias de outros trabalhos da literatura como casos particulares. AlÃm desta generalizaÃÃo, foi possÃvel encontrar outros resultados interessantes como o espessamento da brana e suavizaÃÃo do modelo estudado em 6D. Observaremos tambÃm que a relaÃÃo dos modos quirais à estritamente dependente da escolha do acoplamento de campos utilizado. Para fÃrmions livres, os modos quirais serÃo idÃnticos. Quanto à localizaÃÃo de Modos Massivos, verificaremos que ao reescrever a equaÃÃo de Dirac, obtida a partir de nossa aÃÃo, em uma forma do tipo equaÃÃo de SchrÃdinger, encontraremos um termo de potencial. Estudaremos que ao se utilizar os fatores derivados da sexta dimensÃo como um termo de acoplamento, obteremos resultado semelhante ao de um acoplamento Yukawa em cinco dimensÃes<br>One way to solve the hierarchy problem and therefore unify the fundamental forces is to assume, under the theoretical point of view, that our four-dimensional space (Brane) is housed in a space of higher dimensionality (Bulk). We call all that extra dimension which is not present in our Brana. The idea of extra dimensions to include unification of fundamental forces date from the 30s of last century, with the innovative proposal of Kaluza and Klein, and has been evolving ever since its formulation. Thus, other innovative proposals like that of the work of Randall and Sundrum have created new possibilities for the study, although it is curious that cite not have any experimental evidence to date that these dimensions exist. Fundamental fermionic particles have as one of its interesting properties the existence of left and right chiral modes, this information widely studied in the Standard Model and Supersymmetry in the call. In this article we treat on the location of the chiral modes, massless and massive, the fermionic fields of spin 1/2 in a six-dimensional space of type Conifold solved. This space has an adjustable parameter which allows to recover the geometry of other works of literature. Beyond this generalization was possible to find other interesting results as the thickening of the Brana and smoothing the model studied in 6D. Looking at work that the ratio of chiral modes is strictly dependent on the choice of coupling fields used. For free fermions chiral modes are identical. Regarding the location of Massive modes, we find that by rewriting the Dirac equation, obtained from our action, in a way kind of SchrÃdinger equation, we find a term potential. We found that when using the factors derived from the sixth dimension as a term coupling, we obtain results similar to a Yukawa coupling in five dimensions
41
Karabin, Svyatoslav. "Stelle nel mondo-brana." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2015. http://amslaurea.unibo.it/9566/.
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Lo scopo di questa tesi consiste nello studio delle proprietà generali di sistemi compatti statici e a simmetria sferica nell'ambito dei modelli che prevedono l'esistenza di dimensioni spaziali aggiuntive e che sono comunemente dette del mondo-brana.
Si comincerà con una breve descrizione di teorie gravitazionali a più dimensioni, in particolare si parte dalla teoria di Kaluza-Klein, per arrivare ai modelli ADD(Arkani-Hamed, Dimopoulos, Dvali) e infine a quelli RS(Rundall, Sundrum)che interessano direttamente questo studio.
Per questi modelli, vengono quindi ricavate le equazioni di campo multidimensionali dall'azione di Einstein-Hilbert e successivamente le si proietta, facendo uso delle equazioni di Gauss e Codazzi, su una brana massiva immersa in un “bulk” cinquedimensionale.
Infine si studiano le equazioni di campo di Einstein quadridimensionali per una generica metrica che può servire a descrive stelle statiche, a simmetria sferica e costituite da un fluido perfetto isotropo. Successivamente si ripete la stessa analisi partendo dall'equazione di campo sulla brana e si confrontano i risultati nei due diversi contesti.
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Silva, José Euclides Gomes da. "Sobre modificações na estrutura geométrica em cenários de branas." reponame:Repositório Institucional da UFC, 2013. http://www.repositorio.ufc.br/handle/riufc/8079.
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SILVA, José Euclides Gomes da. Sobre modificações na estrutura geométrica em cenários de branas. 2013. 130 f. Tese (Doutorado em Física) - Programa de Pós-Graduação em Física, Departamento de Física, Centro de Ciências, Universidade Federal do Ceará, Fortaleza, 2013.<br>Submitted by Edvander Pires (edvanderpires@gmail.com) on 2014-05-16T21:35:18Z
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Previous issue date: 2013<br>This thesis presents our proposals for new braneworlds models. Some of the main open issues in high energy physics have interesting solutions assuming the space-time has more than four dimensions. For instance, the hierarchy problem between the eletroweak and the Planck scales, and the origin of the cosmological constant, find some solutions in the brane scenarios. Since these models are rather sensible on the geometrical structure of the multidimensional space time where the brane is embedded, our main goal is to analyze how the geometrical and physical properties of the braneworld and of fields living on it evolve under a geometrical flow in the transverse manifold. The first step was propose an smoothed string-like braneworld with a transverse resolved conifold. The resolution parameter changes the width of the well and the high of the barrier of the Kaluza-Klein modes. Further, the source of this warped solution has different phases depending on the resolution parameter. The massless modes for the scalar, gauge and spinor fields are only well-behaved on the brane for non singular configurations. Another smooth geometrical flow studied was the so-called Ricci flow. This flux posses diffeomorphic invariant solutions called Ricci solitons which are extremals of the energy and entropy functionals. An important two-dimensional Ricci soliton with axial symmetry is the cigar soliton. A warped product between a 3-brane and the cigar soliton turns to be an interior and exterior string-like solution satisfying the dominant energy condition and that supports a massless gravitational mode trapped to the brane. The last geometric modification proposed was the locally Lorentz symmetry violation through a Finsler geometry approach. This anisotropic differential geometry has been intensely studied in last years. We have chosen the so-called bipartite space where the length of the events is measure using the metric and another symmetric tensor called bipartite tensor. We have shown the bipartite space deforms the causal surface to an elliptic cone and provides an anisotropy into the inertia of a particle. By means of an extended Einstein-Hilbert action we have shown an analogy between the bipartite space and the bumblebee and bipartite models which are effective Lorentz violating models in curved space times.<br>A presente tese apresenta nossas propostas de estensões dos modelos de mundo Branas. Alguns dos principais problemas em aberto em física de partículas, como o problema da hieraquia entre as escalas de Planck e eletrofraca, e da cosmologia como a origem da matéria escura e o valor da constante cosmológica, encontram soluções nos cenários de branas. Uma vez que tais modelos são extremamente sensíveis à estrutura geométrica do espaço-tempo ambiente multidimensional no qual a brana está imersa, noss ideia básica é analisar como as propriedades da brana e dos campos que vivem no seu entorno mudam quando alteramos a estrutura geométrica do espaço ambiente. Nosso primeiro passo foi uma estensão do cenário de de brana tipo-corda em seis dimensões onde a variedade transversa é uma seção do cone resolvido. O parâmetro de resolução do cone, que controla a singularidade na origem, também altera a largura dos modos sem massa de um campo escalar e do potencial confinante dos modos Kaluza-Klein. Também analisamos as condições de energia da fonte que passa por diferentes fases durante o fluxo de resolução. Estudamos ainda como este fluxo modifica as propriedades dos campos vetoriais e espinoriais neste cenário. Em seguida, propusemos um novo fluxo geométrico para a variedade transversa. O chamado fluxo de Ricci possui soluções invariantes por difeomorfismos chamadas sólitons de Ricci. Tais soluções têm a propriedade de extremizar grandezas durante esse fluxo, como os funcionais energia e entropia. Uma solução particularmente importante e estacionária deste fluxo é o chamado sóliton charuto de Hamilton que possui simetria axial. Definimos uma variedade produto não-fatorizável entre uma 3-brana e um sóliton de Hamilton resultando em uma solução tipo-corda regular que satisfaz a condição de energia dominante e tem um modo gravitacional não massivo localizado. Outra modificação geométrica proposta foi a Violação da simetria de Lorentz através da introdução de uma estrutura métrica localmente anisotrópica, a chamada geometria de Finsler. Tal abordagem tem sido objeto recente de vários estudos. Escolhemos uma estrutura finsleriana recentemente proposta, chamada bipartite, onde o comprimento dos eventos é calculado não somente com a métrica Lorentziana mas também com uma outra forma bilinear simétrica. O cone de luz desta geometria é deformado para um cone elíptico cujas inclinações das geratrizes dependem dos autovalores do tensor bipartite. Outra propriedade deste espaço-tempo é a de modificar a relação entre o 4-momentum e a 4-velocidade gerando um tensor de inércia. Através de uma ação de Einstein-Hilbert finsleriana em um limite de baixa dependência direcional, encontramos uma analogia entre essa geometria e os modelos bumblebee e aether, que descrevem efetivamente a quebra da simetria de Lorentz em espaços curvos.
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Young, Stephen Christopher. "Stability issues in Kalb-Ramond/dilaton braneworld scenarios." Thesis, 2009. http://hdl.handle.net/2152/ETD-UT-2009-12-699.
Full textAbstract:
I summarize the Randall-Sundrum braneworld scenario, and its application to solving the hierarchy problem in the Standard Model of elementary particles. A generalized Randall-Sundrum scenario is presented, which includes the presence of string-inspired massless Kalb-Ramond and dilaton fields, and includes their backreaction on the metric. It is shown that in such a scenario, solutions exist which can achieve the desired warping on the Standard Model brane, and which stabilize the modulus corresponding to the radius of the extra dimension.<br>text