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Kaluza-klein MonopoleSakarya, Emre 01 September 2007 (has links) (PDF)
Kaluza-Klein theories generally in $(4+D)$ and more specifically in five dimensions are reviewed. The magnetic monopole solutions found in the Kaluza-Klein theories are generally reviewed and their generalizations to Anti-de Sitter spacetimes are discussed.
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Black holes, instability and scalar-tensor gravity / Buracos negros, instabilidade e gravidade escalar-tensorialConsole, Felipe de Carvalho Ceregatti de 25 February 2019 (has links)
In this work, we review three topics which are relevant on its own but which are also interconnected through the AdS/CFT correspondence: (i) black holes in AdS and its thermodynamics, (ii) nonlinear instability of AdS and (iii) scalar- tensor theory of gravity. Each one of these topics find applications in holography using the above mentioned correspondence. We review the various coordinate systems used to write the AdS metric and discuss the main black holes with AdS asymptotics as well as their thermodynamical properties. We also review current results on linear and nonlinear stability for various spacetimes, presenting a heuristic explanation for the nonlinear instability of AdS. The discussion about alternative theories of gravity is restricted to the case of scalar-tensor theories (Horndeski theories, specially). We study the multipole expansion of the electromagnetic field in the solitonic background of a shift-symmetric scalar-tensor model (up to second order in the scalar field coupling constant with the Gauss-Bonnet term). We find that the multipoles are everywhere regular and finite except for the monopole l = 0, which diverges at the origin of the spacetime coordinates. / Neste trabalho, temos como objetivo fazer uma revisão sobre três temas de grande relevância por si só mas, que também se interligam através da correspondencia AdS/CFT: (i) buracos negros em AdS e sua termodinâmica, (ii) a instabilidade não-linear de AdS e (iii) teorias escalar-tensoriais da gravidade. Cada um destes temas encontram aplicações em holografia usando a correspondencia citada acida. Revisamos as diversas formas de escrever a métrica de AdS e discutimos os principais buracos negros assintóticamentes AdS assim como suas propriedades termodinâmicas. Nós também revisamos os resultados atuais sobre a estabilidade linear e não-linear para diversos espaços-tempos, reproduzindo uma explicação heurísitca sobre a instabilidade não-linear do espaço-tempo AdS. A discussão das teorias alternativas à Relatividade Geral é restrita ao caso das teorias escalar-tensorias da gravidade (a teoria de Horndeski, especialmente). Nós estudamos a expansão multipolar do campo electromagnético em um espaço-tempo que é solução do modelo \"shift-symmetric scalar tensor gravity\" (até segunda ordem na constante de acoplamento do campo escalar com o termo de Gauss-Bonnet) com características solitônicas. Encontramos que os multipolos são regulares e finitos em todo espaço-tempo com exceção do monopolo l = 0, que diverge na origem do sistema de coordenadas.
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Quasinormal modes and holographic QCD in gauge/gravity dualityMamani, Luis Alex Huahuachampi January 2017 (has links)
Orientador: Prof. Dr. Vilson Tonin Zanchin / Tese (doutorado) - Universidade Federal do ABC, Programa de Pós-Graduação em Física, 2017. / Nesta tese exploramos alguns aspectos de teorias de campo fortemente acoplados usando o
respectivo dual gravitacional. Comecamos estudando perturbacoes gravitacionais de cordas
negras em rotacao num espaco-tempo assintoticamente Anti-de Sitter (AdS) em quatro dimensoes.
E apresentado uma analise completa do espectro dos modos quasinormais (QNMs),
interpretacoes na teoria de campos dual, quando possivel, sao exploradas. No setor escalar das perturbacoes obtemos as relacoes de dispersao na aproximacao hidrodinamica seguindo tres abordagens: perturbacoes gravitacionais, flutuacoes hidrodinamicas de um fluido relativista em (2+1) dimensoes e uma analise de vetores de onda relativistas. Os resultados obtidos no limite hodrodinamico mostram efeitos relativistas como a contracao de Lorentz, dilatacao do tempo de amortecimento e o efeito Doppler da frequencia. Os resultados numericos tambem mostram um crossover do regime hidrodinamico para o relativista e do regime nao hidrodinamico para o relativista, o ultimo para o primeiro modo nao hidrodinamico. Adicionalmente reportamos o surgimento de uma nova classe de modos quasinormais. Na segunda parte exploramos modelos fenomenologicos para a cromodinamica quantica (QCD). Primeiramente, exploramos um modelo holografico para mesons vetoriais no contexto do modelo soft-wall, exploramos o derretimento desses estados de quasiparticula quando a temperatura e adicionado atraves de um buraco negro no fundo gravitational. Tambem calculamos os modos quasinormais neste modelo e as relacoes de dispersao neste modelo. Seguimos um procedimento semelhante para explorar o derretimendo dos mesons escalares. A diferencia em relacao aos mesons vetoriais e que pode ser introduzido um dilaton quartico no regime do ultravioleta (UV) para descrever o condensado de gluons, enquanto que o comportamento linear do espectro de massas e confinamento e garantido por um dilaton quadratico no regime do infravermelho (IR). Exploramos os efeitos da escala de energia associado com o condensado de gluons no espectro e derretimento dos mesons escalares.
na ultima parte apresentando um modelo holografico para descrever o setor dos gluons
do Lagrangiano de Yang-Mills implementado atraves do acoplamento do campo dilaton com
a metrica. Neste contexto calculamos o espectro de massas do setor escalar e tensorial do
campo dos gluons. Os resultados obtidos sao consistentes com os resultados da QCD na rede. Tambem calculamos o valor esperado do vacuo (VEV) e a densidade de energia do vacuo
da QCD, ambos os resultados sao resoaveis comparados com os resultados disponiveis na
literatura. No final, e proposto um novo dicionario relacionando a anomalia do traco de teorias 10 de campo conforme deformadas com a anomalia do traco da QCD. Como uma consequencia nao trivial deste dicionario observamos o surgimento de uma funcao-¿À semelhante ao resultado em QCD perturbativa a dois loops. / In this thesis we explore some aspects of strongly coupled field theories using the respective
gravitational duals. We start studying gravitational perturbations of rotating black
strings in asymptotically Anti-de Sitter (AdS) four-dimensional spacetime. A complete analysis
of the spectrum of the quasinormal modes (QNMs) is presented, interpretations in the
dual field theory, when possible, are explored. In the scalar sector of the perturbations we obtain the dispersion relations in the hydrodynamic approximation following three approaches:
gravitational perturbations, hydrodynamic fluctuations of a relativistic fluid in (2+1) dimensions and an analysis of relativistic wave vectors. The results obtained in the hydrodynamic limit show relativistic effects like Lorentz contraction, damping time dilation and Doppler shift of the frequency. The numerical results also show a crossover from the hydrodynamicto- relativistic regimes and from the non-hydrodynamic-to-relativistic regimes, the last for the first non-hydrodynamic quasinormal mode (QNM). Additionally we report the emergence of a new class of QNMs.
In the second part we explore phenomenological models for quantum chromodynamics
(QCD). Firstly we explore a holographic model for vector mesons in the context of the softwall
model. We explore the melting of these quasiparticle states when the temperature is
added via a black hole on the gravitational background. We also calculate the quasinormal
modes and the dispersion relations in this model. We follow a similar procedure to explore the melting of scalar mesons. The difference in relation to the vector mesons case is that a quartic dilaton in the ultraviolet (UV) regime can be introduced to describe the gluon condensate, while the linear behaviour of the mass spectrum and confinement is guaranteed by a quadratic dilaton field infrared (IR) regime. We explore the effects of the energy scale associated with the gluon condensate in the mass spectrum and melting of the scalar mesons.
In the last part we present a holographic model to describe the gluon sector of the Yang-
Mills Lagrangian implemented through the coupling of the dilaton field to the metric. In this
context we calculate the mass spectrum of the scalar and tensor sectors of the gluons field. The results obtained are consistent with lattice QCD. We also calculate the vacuum expectation value (VEV) and the energy density of the QCD vacuum, both results are reasonable compared with results currently available in the literature. At the end a new dictionary is proposed, which relates the trace anomaly of deformed conformal field theories (CFTs) to the trace anomaly of QCD. As a non trivial consequence of this dictionary we observe the emergence of a â function similar to the two loops result in perturbative QCD.
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Studium geometrických a fyzikálních vlastností přesných prostoročasů / Investigation of geometrical and physical properties of exact spacetimesHruška, Ondřej January 2019 (has links)
In this work, we study geometrical and physical properties of exact spacetimes that belong to non-expanding Pleba'nski-Demia'nski class. It is a family of solutions of type D that also belong to the Kundt class, and contain seven arbitrary parameters including a cosmological constant. We present here the results of three extensive articles, each focusing on a different aspect of the problem. In the first article, we investigate the meaning of individual parame- ters in the non-expanding Pleba'nski-Demia'nski metric. First, we set almost all parameters to zero and obtain Minkowski and (anti-)de Sitter backgrounds. Af- terwards, we allow other parameters to be non-zero and we study the B-metrics, non-singular "anti-NUT" solutions and conclude with the full electrovacuum Pleba'nski-Demia'nski metric. In the second article, we focus on the de Sitter and anti-de Sitter backgrounds where we present and analyse 11 new diagonal metric forms of (anti-)de Sitter spacetime. We find five-dimensional parametriza- tions, draw coordinate surfaces and conformal diagrams. In the third article, we show that the AII-metric together with the BI-metric describes gravitational field around a tachyon on both Minkowski and (anti-)de Sitter backgrounds. Fi- nally, in order to better understand the global structure and...
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Influência das Cordas Cósmicas não-Abelianas na Geometria do Espaço-tempoSantos, Antônio de Pádua 25 February 2016 (has links)
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Previous issue date: 2016-02-25 / Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq / In this thesis, we study the influence of gravitating non-Abelian cosmic strings on the spacetime
geomerty. In order to develop this analysis, we constructed a set of coupled non-linear
differential equations. Because there is no closed solution for this set of equations, we solve
it numerically to determine the behaviour for the Higgs, gauge and metric fields. This model
under consideration present two bosonic sectors, besides the non-Abelian gauge field. The two
bosonic sectors may present a direct coupling. So, we investigate the relevance of this coupling
on the system, specifically in the linear energy density of the string and on the planar angle
deficit. We also analyze the behaviors of these quantities as function of the energy scale where
the gauge symmetry is spontaneously broken. We have extented this analysis to de Sitter and
anti-de Sitter spacetimes. In order to do that we construct the complete set of equations of
motion considering the presence of a cosmological constant. By using numerical analysis we
provide the behavior of the Higgs and gauge fields and also for the metric tensor for specific
values of the physical parameters of the theory. For de Sitter case, we find the appearance
of horizons that although being consequence of the presence of the cosmological constant it
strongly depends on the value of the gravitational coupling. In the anti-de Sitter case, we find
that the system does not present horizons. In fact the new feature of this system is related
with the behavior of the (tt) and (zz) components of the metric tensor. They present a strongly
increasing for large distance from the string. / Nesta tese estudamos a influência das cordas cósmicas não-Abelianas na geometria do
espaço-tempo. Para este fim, utilizamos um modelo de Higgs não-Abeliano acoplado com
a gravidade e obtemos um sistema de equações diferenciais não-lineares. Como este sistema
de equações diferenciais não possui solução analítica, realizamos análise numérica para obter
o comportamento dos campos de Higgs, de gauge e métricos em função da distância à
corda cósmica. O modelo considerado apresenta dois campos bosônicos e um campo de gauge
não-Abeliano. Como os dois setores bosônicos podem apresentar um acoplamento direto, investigamos
a relevância deste acoplamento no sistema, especificamente na densidade linear de
energia e no déficit de ângulo planar. Também analisamos o comportamento destas quantidades
como função da escala de energia onde a simetria de gauge é espontaneamente quebrada.
Ampliamos este estudo para as cordas cósmicas não-Abelianas no espaço-tempo de de Sitter
e anti-de Sitter. Para isto, construímos um sistema de equações de campo considerando a presença
da constante cosmológica. Utilizando a análise numérica, fornecemos o comportamento
dos campos de Higgs, de gauge e dos campos métricos para valores específicos dos parâmetros
físicos do modelo. Para o caso do espaço-tempo de de Sitter, salientamos o surgimento do horizonte
cosmológico que, embora seja consequência da constante cosmológica, está fortemente
relacionado ao acoplamento gravitacional. Para o espaço-tempo de anti-de Sitter, encontramos
que o sistema não apresenta horizonte. Esta característica do sistema está relacionada às componentes
(tt) e (zz) do tensor métrico, que divergem para grandes distâncias da corda cósmica.
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Dualities, Symmetries and Unbroken Phases in String Theory : Probing the Composite Nature of the String / Dualiteter, Symmetrier och Obrutna Faser i Strängteori : En Utforskning av Strängens Sammansatta NaturEngquist, Johan January 2005 (has links)
The thesis treats aspects of string/M-theory in anti-de Sitter spacetimes and their supersymmetric completions. By applying the AdS/CFT correspondence, as well as models of spin chains and singletons, we try to attain a better understanding of the underlying symmetries and the unbroken phases of string/M-theory. Tensionless string/M-theory in anti-de Sitter spacetime is argued to imply a higher spin gauge symmetry enhancement and to be described by gauged sigma models of multi-singletons as well as by closed singleton strings. Vasiliev's weakly projected equations of symmetric massless higher spin gauge fields in the vector oscillator formulation is shown to follow from a deformation of the singleton model. Various four dimensional minimal as well as non-minimal supersymmetric higher spin gauge theories in the spinor formulation are examined. The minimal higher spin gauge theory based on the symmetry algebra hs(1|4) is elaborated on in an N=1 superspace, illustrating the remarkable fact that the choice of base manifold is not fixed in unfolded dynamics. The importance of the representations saturating the unitarity bounds in anti-de Sitter spacetime is stressed throughout the thesis, with particular emphasis on the singleton and the massless representations. Singletons, and hence massless states, are shown to appear as bound states on the string or p-brane and are localized at cusps. Furthermore, we examine semiclassical string solutions in Type IIB String Theory in AdS(5) x S(5) and their boundary duals in N=4 Super Yang-Mills Theory in d=4 which are constituted out of thermodynamic composite operators. By using integrable spin chain techniques and Bäcklund transformations in the field theory and in the string theory, respectively, the one-loop anomalous dimensions as well as the tower of conserved charges of the composite operators are shown to be in agreement with the energies and the tower of conserved charges associated with the dual string states.
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