The AdS/CFT correspondence and its extensions to more general gauge/gravity dualities have provided a powerful framework for the study of strongly coupled gauge theories. This thesis explores properties of a large class of thermal strongly coupled gauge theories using the gravity dual. In order to bring the holographic framework closer to Quantum Chromodynamics (QCD), we study theories with matter in the fundamental representation. In particular, we focus on the holographic dual of SU(Nc) supersymmetric Yang-Mills theory coupled to Nf<<Nc flavours of fundamental matter at finite temperature, which is realised as Nf Dq-brane probes in the near horizon (black hole) geometry of Nc black Dp-branes. We explore many aspects of these Dp/Dq brane systems, often focussing on the D3/D7 brane system which is dual to a four dimensional gauge theory. We study the thermodynamics of the Dq-brane probes in the black hole geometry. At low temperature, the branes sit outside the black hole and the meson spectrum is discrete and possesses a mass gap. As the temperature increases, the branes approach a critical solution. Eventually, they fall into the horizon and a phase transition occurs. At large Nc and large 't Hooft coupling, we show that this phase transition is always first order. We calculate the free energy, entropy and energy densities, as well as the speed of sound in these systems. We compute the meson spectrum for brane embeddings outside the horizon and find that tachyonic modes appear where this phase is expected to be unstable from thermodynamic considerations. We study the system at non-zero baryon density nb and find that there is a line of phase transitions for small nb, terminating at a critical point with finite nb. We demonstrate that, to leading order in Nf/Nc, the viscosity to entropy density ratio in these theories saturates the conjectured universal bound. Finally, we compute spectral functions and diffusion constants for fundamental matter in the high temperature phase of the D3/D7 theory.

In the following thesis, I will conduct a thermodynamic analysis of the Taub-NUT spacetime in various dimensions, as well as show uses for Taub-NUT and other Hyper-Kahler spacetimes. <br /><br /> Thermodynamic analysis (by which I mean the calculation of the entropy and other thermodynamic quantities, and the analysis of these quantities) has in the past been done by use of background subtraction. The recent derivation of the (A)dS/CFT correspondences from String theory has allowed for easier and quicker analysis. I will use Taub-NUT space as a template to test these correspondences against the standard thermodynamic calculations (via the N&ouml;ether method), with (in the Taub-NUT-dS case especially) some very interesting results. <br /><br /> There is also interest in obtaining metrics in eleven dimensions that can be reduced down to ten dimensional string theory metrics. Taub-NUT and other Hyper-Kahler metrics already possess the form to easily facilitate the Kaluza-Klein reduction, and embedding such metrics into eleven dimensional metrics containing M2 or M5 branes produces metrics with interesting Dp-brane results.

The AdS/CFT correspondence and its extensions to more general gauge/gravity dualities have provided a powerful framework for the study of strongly coupled gauge theories. This thesis explores properties of a large class of thermal strongly coupled gauge theories using the gravity dual. In order to bring the holographic framework closer to Quantum Chromodynamics (QCD), we study theories with matter in the fundamental representation. In particular, we focus on the holographic dual of SU(Nc) supersymmetric Yang-Mills theory coupled to Nf<<Nc flavours of fundamental matter at finite temperature, which is realised as Nf Dq-brane probes in the near horizon (black hole) geometry of Nc black Dp-branes. We explore many aspects of these Dp/Dq brane systems, often focussing on the D3/D7 brane system which is dual to a four dimensional gauge theory. We study the thermodynamics of the Dq-brane probes in the black hole geometry. At low temperature, the branes sit outside the black hole and the meson spectrum is discrete and possesses a mass gap. As the temperature increases, the branes approach a critical solution. Eventually, they fall into the horizon and a phase transition occurs. At large Nc and large 't Hooft coupling, we show that this phase transition is always first order. We calculate the free energy, entropy and energy densities, as well as the speed of sound in these systems. We compute the meson spectrum for brane embeddings outside the horizon and find that tachyonic modes appear where this phase is expected to be unstable from thermodynamic considerations. We study the system at non-zero baryon density nb and find that there is a line of phase transitions for small nb, terminating at a critical point with finite nb. We demonstrate that, to leading order in Nf/Nc, the viscosity to entropy density ratio in these theories saturates the conjectured universal bound. Finally, we compute spectral functions and diffusion constants for fundamental matter in the high temperature phase of the D3/D7 theory.

The low-energy supersymmetry phenomenology for specific classes of string compactifications is investigated given that the low-energy physics may provide a clue as to the structure of the fundamental theory at high energy scales. The one-parameter model (OPM), a highly constrained subset of minimal Supergravity where all the soft-supersymmetry breaking terms may be fixed in terms of the gaugino mass, is studied, in addition to a three-family Pati-Salam model constructed from intersecting D6-branes. Furthermore, the phenomenology of gravity mediated supersymmetry breaking F-theory SU(5) and SO(10) models, as well as F-SU(5) models with vector- like particles, are examined. We determine the viable parameter space that satisfies all the latest experimental constraints, including the most recent WMAP relic neutralino abundance observations, and find it to be consistent with the CDMS II and other concurrent direct-detection experiments. Moreover, we compute the gamma-ray flux and cross-sections of neutralino annihilations into gamma-rays and compare to the published Fermi-LAT satellite telescope measurements. In F-theory SU(5) and SO(10) models, we predict the exact small deviation of the gaugino mass relation at two-loop level near the electroweak scale, which can be tested at the colliders. More- over, in F-SU(5), we predict the precise deviations from the mSUGRA gaugino mass relations due to the presence of the vector-like particles, also testable at the colliders. The compilation of all these results form a comprehensive collection of predictions with which to evaluate these string models alongside anticipated experimental dis- coveries in the coming decade.

Dans cette thèse nous étudions la théorie des cordes en présence de<br />D-branes et éventuellement d'orientifolds dans des espaces courbes ou dépendants du temps. Notre étude vise à comprendre certains aspects des espaces courbes et dépendant du temps, notamment à cause de leur importance en cosmologie.<br /><br />Le premier chapitre introduit quelques bases de la théorie des cordes.<br /><br />Le deuxième chapitre étudie les cordes non orientées sur les groupes compacts SU(2) et SO(3) : après un rappel des résultats connus sur les D-branes dans ces espaces, nous présentons nos résultats sur la position des orientifolds et leur interaction avec les cordes ouvertes et fermées.<br /><br />Le troisième chapitre étudie les D-branes dans certains fonds de type Ramond-Ramond, en utilisant la S-dualité qui les relie à des fonds de type Neveu-Schwarz, où on sait faire les calculs.<br /><br />Le dernier chapitre considère les cordes sur une D-brane parcourue par une onde plane, et introduit les outils y permettant l'étude des interactions.

Η παρούσα διπλωματική εργασία αποτελεί μια σύντομη εισαγωγή στη θεωρία των Χορδών, ενώ ιδιαίτερη έμαφαση έχει δοθεί στις D-Branes. Αρχικά παρουσιάζεται η κλασική μποζονική χορδή, καθώς και η κβάντωσή της. Στη συνέχεια περιγράφεται ο Τ-δυϊσμός και εισάγονται οι D-Branes στη θεωρία, των οποίων και αναλύονται τα βασικά χαρακτηριστικά, ενώ παρουσιάζεται και η δράση κοσμικού όγκου για την περιγραφή τους. Ακολουθεί μια συνοπτική περιγραφή των υπερσυμετρικών χορδών και των διαφορετικών θεωριών χορδών που προκύπτουν. Τέλος, παρουσιάζεται η γεωμετρία που παράγουν οι D-Branes, σε αναλογία με την αντίστοιχη των μελανών οπών, και περιγράφεται ο τρόπος με τον οπίο κατασκευάζονται extremal μελανές οπές στη θεωρία χορδών καθώς και η μικροσκοπική περιγραφή τους μέσω κατάλληλων διατάξεων από D-Branes. / This thesis consists of a short introduction to string theory, while emphasis has been given on D-Branes. First, the classical bosonic string is presented, and its quantization. T-duality is described and D-Branes are introduced in the theory, the basic properties of which are analyzed. A short discussion of supersymmetric strings follows. Finally, the geometry of D-branes is presented, with respect to the geometry of black holes, and the way that extremal black holes are constructed in string theory, while also their microscopic describtion in terms of D-branes.

Thesis (M.S.)--Brigham Young University. Dept. of Physics and Astronomy, 2007. / Includes bibliographical references (p. 96-98).

ARAÚJO, Júlio César Brasil de. Extensões de cenários de Branas com defeitos do tipo corda em seis dimensões. 2012. 52 f. Dissertação (Mestrado em Física) - Programa de Pós-Graduação em Física, Departamento de Física, Centro de Ciências, Universidade Federal do Ceará, Fortaleza, 2012. / Submitted by francisco lima (admir@ufc.br) on 2014-07-02T17:02:38Z No. of bitstreams: 1 2012_dis_jcdearaujo.pdf: 375967 bytes, checksum: 01abb06adcc382168180a8e7c755d8fc (MD5) / Approved for entry into archive by Edvander Pires(edvanderpires@gmail.com) on 2014-08-06T20:43:37Z (GMT) No. of bitstreams: 1 2012_dis_jcdearaujo.pdf: 375967 bytes, checksum: 01abb06adcc382168180a8e7c755d8fc (MD5) / Made available in DSpace on 2014-08-06T20:43:37Z (GMT). No. of bitstreams: 1 2012_dis_jcdearaujo.pdf: 375967 bytes, checksum: 01abb06adcc382168180a8e7c755d8fc (MD5) Previous issue date: 2012 / The purpose of this work is to show an expanse about Gherghetta-Shaposhnikov (GS) scenery through the introduction of a dimensionless parametric in the warped geometry in six dimensions, we suppose which our universe the way that we watch is stood for minkowsk’s 3-brane and the two other are additional dimensions and one of them is compact. In that new model, we are able to achieve the linear process about Einstein’s equation. In order to achieve a perturbation in the metric, so that we are able to locate the equation of motion, consequently finding the massless gravity model. Through these procedures, we have new results about the geometry and physics states in that new scenery. In that new scenery we order the gravity location in a 6-dimensinal geometry, in order to showing an instant where we can find the gravity location, then we get this type of location through an expansion of the GS’s model. / O objetivo deste trabalho é apresentar uma extensão do cenário Gherghetta-Shaposhnikov (GS) através da introdução de um parâmetro adimensional em uma geometria não-fatorizável em seis dimensões, onde supomos que o nosso universo observável é representado por uma 3-brana minkowskiana e as outras duas são dimensões extras, com uma delas compacta. Neste modelo, realizamos o processo de linearização das equações de Einstein fazendo uso de um método perturbativo, a fim de encontrarmos as equações de movimento para em seguida localizarmos o modo-zero gravitacional. A partir desses procedimentos, novos resultados foram obtidos no tocante as propriedades físicas e geométricas desse novo cenário. Com este novo modelo sistematizamos a localização de gravidade em uma geometria 6-dimensional, exibindo um exemplo onde ocorre localização de gravidade e obtendo esse resultado através de uma extensão do modelo GS.

ARAÚJO, Júlio César Brasil de. Extensões de cenários de Branas com defeitos do tipo corda em seis dimensões. 2012. 52 f. Dissertação (Mestrado em Física) - Programa de Pós-Graduação em Física, Departamento de Física, Centro de Ciências, Universidade Federal do Ceará, Fortaleza, 2012. / Submitted by Edvander Pires (edvanderpires@gmail.com) on 2015-10-20T17:55:03Z No. of bitstreams: 1 2012_dis_jcbaraujo.pdf: 397232 bytes, checksum: 9f930f4809299b920bbd8ba8bb7f7fa3 (MD5) / Approved for entry into archive by Edvander Pires(edvanderpires@gmail.com) on 2015-10-20T21:03:03Z (GMT) No. of bitstreams: 1 2012_dis_jcbaraujo.pdf: 397232 bytes, checksum: 9f930f4809299b920bbd8ba8bb7f7fa3 (MD5) / Made available in DSpace on 2015-10-20T21:03:04Z (GMT). No. of bitstreams: 1 2012_dis_jcbaraujo.pdf: 397232 bytes, checksum: 9f930f4809299b920bbd8ba8bb7f7fa3 (MD5) Previous issue date: 2012 / The purpose of this work is to show an expanse about Gherghetta-Shaposhnikov (GS) scenery through the introduction of a dimensionless parametric in the warped geometry in six dimensions, we suppose which our universe the way that we watch is stood for minkowsk’s 3-brane and the two other are additional dimensions and one of them is compact. In that new model, we are able to achieve the linear process about Einstein’s equation. In order to achieve a perturbation in the metric, so that we are able to locate the equation of motion, consequently finding the massless gravity model. Through these procedures, we have new results about the geometry and physics states in that new scenery. In that new scenery we order the gravity location in a 6-dimensinal geometry, in order to showing an instant where we can find the gravity location, then we get this type of location through an expansion of the GS’s model. / O objetivo deste trabalho é apresentar uma extensão do cenário Gherghetta-Shaposhnikov (GS) através da introdução de um parâmetro adimensional em uma geometria não-fatorizável em seis dimensões, onde supomos que o nosso universo observável é representado por uma 3-brana minkowskiana e as outras duas são dimensões extras, com uma delas compacta. Neste modelo, realizamos o processo de linearização das equações de Einstein fazendo uso de um método perturbativo, a fim de encontrarmos as equações de movimento para em seguida localizarmos o modo-zero gravitacional. A partir desses procedimentos, novos resultados foram obtidos no tocante as propriedades físicas e geométricas desse novo cenário. Com este novo modelo sistematizamos a localização de gravidade em uma geometria 6-dimensional, exibindo um exemplo onde ocorre localização de gravidade e obtendo esse resultado através de uma extensão do modelo GS.

Este é um trabalho de revisão. Os principais formalismos no desenvolvimento da teoria de cordas são introduzidos e discutidos: a corda bosônica e as supercordas no formalismo de Ramond-Neveu-Schwarz e no formalismo de Green-Schwarz. São introduzidas também as açôes efetivas no limite de baixas energias das D-branas (ação DBI) e das teorias de supergravidade (D=10,11). Por fim, são analisados alguns aspectos da correspondência AdS/CFT, enunciando a conjectura e introduzindo algumas das entradas do dicionário. Os apêndices contêm tópicos de grande relevância para o texto e podem ajudar a esclarecer vários raciocínios e passagens ao longo do mesmo. / This is a review work. The main formalisms on the development of string theory are introduced and discussed: the bosonic string and the superstrings formalisms of Ramond-Never-Schwarz and Green-Schwarz. The effective actions in the low energy limit of the D-branes (DBI action) and supergravity theories (D=10,11) are introduced as well. Finally, some aspects of the AdS/CFT correspondence are analised, enunciating the conjecture and introducing some entries of the dictionary. The appendices contains some topics that are highly relevant for the whole text and may help clarify several ideas and arguments through it.