In this thesis we consider the quantum measurement properties of a driven cavity with a Kerr-type nonlinearity where the signal to be measured is a dispersively coupled qubit. Focusing on an operating regime that is near a bifurcation point,we calculate analytic expressions for the backaction dephasing rate and measurement rate beyond leading-order perturbation theory. This is done by using a phase-space approach which accounts for cavity noise squeezing. We consider two different methods to obtain an analytic result: the first is using an approximation common in the literature, the cavity dynamics are linearized with respect to the average photon number of the uncoupled cavity. With this linearization the physics of the nonlinear cavity maps to that of a degenerate parametric amplifier (DPA) with a detuned pump. The second method takes into account the displacement of the average cavity state when the qubit is in one of its eigenstates. Linearizing the cavity with respect to this {\it displaced} state takes this method beyond the DPA approach. Surprisingly, we find that increasing the coupling strength beyond the regime described by leading-order perturbation theory (i.e. linear response) allows one to come significantly closer to the quantum limit on the measurement efficiency. Moreover, we show that the approach which includes this displacement effect results in different behavior when evaluating how close one can approach the quantum limit. This provides a general framework for investigating quantum measurement with driven nonlinear systems beyond weak coupling. Finally, we interpret these results in terms of the non-Gaussian photon number fluctuations of the nonlinear cavity. Our results are relevant to recent experiments using superconducting microwave circuits to study quantum measurement. / Dans cette thèse nous abordons des questions relatives à une cavité resonante nonlinéaire couplée à un qubit en régime dispersif. Nous nous concentrons sur un regime qui est proche d'un point de bifurcation et nous calculons des expressions analytiques pour le taux de mesures et le taux du déphasage. Nos calculs sont fait au-delà de la théorie de la perturbation et sont valides pour des couplages généraux. Nous utilisons une méthode qui tient en compte du resserrement du bruit dans la cavité.Nous considerons deux façons differentes pour obtenir un résultat analaytique. La première est une approximation courante qui consiste à linéariser les équations du mouvement grâce à un nombre élevé de photons dans la cavité. Avec cette approximation la dynamique du systeme devient celle d'un amplificateur parametrique dégeneré (DPA) avec pompe desaccordée.La deuxième façon tient compte de la modification de l'état moyen de la cavité en fonction de l'état propre du qubit. La cavité est linéarizée en funtion de ce nouvel état, ce qui rend la méthode plus précis que la première. Étonnamment, ces méthodes nous indiquent qu'il est préférable d'avoir un couplage plus élevé que celui permit par la théorie des perturbations afin de s'approcher de la limite quantique. Cette façon nous donne un cadre général pour étudier des systems quantiques nonlinéares.Finalement, nous interprètons nos résultats en termes des fluctuations non-Gaussiens du nombre de photons dans la cavité. Nos résultats sont pertinents dans le cadre d'expériences récentes, en particulier pour des circuits supraconducteurs.

We give an overview of flux compactification and a brief introduction to the present challenges in embedding inflation into string theory. With these challenges in mind, we suggest a novel string theory setup in which to study brane inflation. We construct a deformation of the warped resolved conifold background with supersymmetry breaking ISD (1,2) fluxes by adding D7--branes. We find spontaneous supersymmetry breaking without generating a bulk cosmological constant. In the compactified form, our background will no longer be a Calabi--Yau manifold. In the presence of D7--branes, the (1,2) fluxes can give rise to non-trivial D-terms. We study the Ouyang embedding of D7--branes and find that in this case the D--terms are indeed non-zero. In the limit when we approach the singular conifold, the D--terms vanish for Ouyang's embedding, although supersymmetry is broken. We discuss the puzzle of determining the correct 4D supergravity superpotential and suggest an approach to study the inflationary dynamics in this background. / Nous donnons un survol de la compactification des flux dans la théorie des supercordes, ainsi qu'une brève introduction aux défis présents dans la réalisation de l'inflation par le biais de la théorie des cordes. Nous proposons ainsi une concrétisation originelle de l'inflation due aux branes. En ajoutant des branes D7 à la théorie de type IIB, nous construisons une modification d'un fond de variété conique déformée à l'aide de flux auto-duaux imaginaires ISD(1,2) brisant la supersymmétrie, sans toutefois générer de constante cosmologique dans le volume. Dans sa forme compactifiée notre fond ne sera plus une variété Calabi-Yau, puisqu'une classe de Chern non-nulle sera permise. En présence des branes D7, les flux (1,2) peuvent de plus générer des termes D non-triviaux. Nous étudions le plongement Ouyang de branes D7 et trouvons que dans ces cas, les termes D sont effectivement non-nuls. Dans la limite de la variété conique singulière, les termes D deviennent zéro pour le plongement de Ouyang, alors que la supersymmétrie paraît être brisée. Nous discutons du problème de la détermination du superpotentiel effectif en 4 dimensions, et suggérons une approche pour l'étude de la dynamique de l'inflation dans ce contexte.

<p> The kinematics and dynamics for plane wave optics are derived for a massive electrodynamic field by utilizing Proca's theory. Atomic spectroscopy is also examined, with the focus on the 21 cm radiation due to the hyperfine structure of hydrogen. The modifications to Snell's Law, the Fresnel formulas, and the 21 cm radiation are shown to reduce to the familiar expressions in the limit of zero photon mass.</p>

<p> In this dissertation, scenarios where strong conformal dynamics constitutes the ultraviolet completion of the physics that drives electroweak symmetry breaking are considered. It is shown that in theories where the operator responsible for the breaking of conformal symmetry is close to marginal at the breaking scale, the dilaton mass can naturally lie below the scale of the strong dynamics. However, in general this condition is not satisfied in the scenarios of interest for electroweak symmetry breaking, and so the presence of a light dilaton in these theories is associated with mild tuning. The effective theory of the light dilaton is constructed in this framework, and the form of its couplings to Standard Model states are determined. It is shown that corrections to the form of the dilaton interactions arising from conformal symmetry violating effects are suppressed by the square of the ratio of the dilaton mass to the strong coupling scale, and are under good theoretical control. These corrections are generally subleading, except in the case of dilaton couplings to marginal operators, when symmetry violating effects can sometimes dominate. Phenomenological implications of these results are investigated for models of technicolor, and for models of the Higgs as a pseudo-Nambu-Goldstone boson, that involve strong conformal dynamics in the ultraviolet.</p><p> Using AdS/CFT correspondence, a holographic realization of this scenario is obtained by constructing the effective theory of the graviscalar radion in the Randall-Sundrum models, taking stabilization into account. The conditions under which the radion can remain light are explored, and the corrections to its couplings to Standard Model (SM) states localized on the visible brane are determined. It is shown that in the theories of interest for electroweak symmetry breaking that have a holographic dual, the presence of a light radion requires mild tuning. Corrections to the form of the radion coupling to SM states arising from effects associated with brane stabilization are also calculated. These corrections scale as the square of the ratio of the radion mass to the Kaluza-Klein scale, and are generally subleading, except in the case of gluons and photon, when they can sometimes dominate. These results are in agreement with and lend robustness to the conclusions for the dilaton.</p>

Dark Matter: The evidence for the existence of Dark Matter is compelling based on observations in Astrophysics and Cosmology, while the nature of Dark Matter in Particle Physics is still unclear. Direct Detection is a promising method to detect the recoil energy of nucleons from the scattering of Dark Matter, and indirect searches for Dark Matter put constraints on Dark Matter annihilation and decay, and they give hints about the properties of Dark Matter. We proposed a Millicharged Atomic Dark Matter model, in which the dark constituents of the hidden sector are bound into dark atoms by an unbroken hidden U(1) gauge field. This model is consistent with cosmological and astrophysical constraints, it has the potential to explain the results from the CoGeNT experiment, and it relaxes some tensions from other direct search experiments.UV/IR Divergences in Inflation: Studying the quantum corrections to the two point correlation function of curvature perturbations is an essential step to understand perturbation theory in curved space time. IR divergences may lead to possibly observable consequences in cosmology. By finding the correct way to impose UV and IR cutoffs, we manage to reach a consistent result that all three regularization schemes commonly used -- brute-force cutoff, dimensional regulation, and Pauli-Villars regularization -- all give the same quantum correction to the correlation function. By considering the IR divergences from entropy fields, we explore the effective field theory of inflation in the presence of such fields. / Matière Noire:Les observations actuelles en astrophysique et en cosmologie semblent démontrer l'existence de matière noire dans notre univers. Néanmoins, du point de vue des intéractions fondamentales en physique des particules, les propriétés d'une telle matière ne sont pas encore complètement établies. Les méthodes de détection directe et indirecte apportent de nouvelles limites sur les modes de desintégration de la matière noire et améliorent notre compréhension de celle-ci. Cette thèse propose un modèle de matière noire atomique millichargée, dans lequel l'atome est consitué de particules sombres fondamentales liées par une force de jauge invisible aux particules du modèle standard. Ce modèle est ensuite comparé aux contraintes mentionnées, et en particulier aux résultats de l'expérience CoGeNT, permettant ainsi une meilleure intégration des differentes données experimentales. Divergences ultraviolette et infrarouge dans l'inflation cosmologique:L'étude des corrections quantiques dans la fonction de corrélation de deux perturbations de la courbure spatiale est un ingrédient essentiel a la compréhension de la théorie des perturbations dans un espace-temps courbe. Les divergences infrarouge peuvent causer des effets mesurables en cosmologie. En choisissant de manière appropriée les bornes d'intégration d'énergie, les corrections de la fonction de corrélation sont calculées dans les trois grands procédures de régularisation. La théorie effective de l'inflation cosmologique est ensuite présentée avec les effets des divergences infrarouges des champs d'entropie.

<p> Spin networks arise in many areas of physics and are a key component in both the canonical formulation (loop quantum gravity) and the path-integral formulation (spin-foam gravity) of quantum gravity. In loop quantum gravity the spin networks are used to construct a countable basis for the physical Hilbert space of gravity. The basis states may be interpreted as gauge-invariant wavefunctionals of the connection. Evaluating the wavefunctional on a specific classical connection involves embedding the spin network into a spacelike hypersurface and finding the holonomy around the network. This is equivalent to evaluating a ''<i>g</i>-inserted'' spin network (a spin network with a group action acting on all of the edges of the network). The spin-foam approach to quantum gravity is a path-integral formulation of loop quantum gravity in which the paths are world-histories of embedded spin networks. Depending on the spin-foam model under consideration the vertex amplitude (the contribution a spin-foam vertex makes to the transition amplitude) may be represented by a specific simple closed spin network. The most important examples use the 6<i>j</i>-symbol, the 15<i>j</i>-symbol, and the Riemannian 10<i>j</i>-symbol. The semiclassical treatment of spin networks is the main theme of this dissertation. </p><p> To show that classical solutions of general relativity emerge in the appropriate limits of loop quantum gravity or spin-foam gravity requires knowledge of the semiclassical limits of spin networks. This involves interpreting the spin networks as inner products and then treating the inner products semiclassically using the WKB method and the stationary phase approximation. For any given spin network there are many possible inner product models which correspond to how the spin network is ''split up'' into pieces. For example the 6<i> j</i>-symbol has been studied in both a model involving four angular momenta (Aquilanti et al 2012) and a model involving twelve angular momenta (Roberts 1999). Each of these models offers advantages and disadvantages when performing semiclassical analyses. Since the amplitude of the stationary phase approximation relies on determinants they are easiest to calculate in phase spaces with the fewest dimensions. The phase, on the other hand, is easiest to compute in cases where all angular momenta are treated on an equal footing, requiring a larger phase space. </p><p> Surprisingly, the different inner product models are <i>not</i> related by symplectic reduction (the removal of a symmetry from a Hamiltonian system). There <i>is</i> a connection between the models, however. On the level of linear algebra the connection is made by considering first not inner products but matrix elements of linear operators. A given matrix element can then be interpreted as an inner product in two different Hilbert spaces. We call the connection between these two inner product models the ''remodeling of an inner product.'' The semiclassical version of an inner product remodeling is a generalization of the idea that the phase space manifold that supports the semiclassical approximation of a unitary operator may be considered the graph of a symplectomorphism. We use the manifold that supports the semiclassical approximation of the linear map to ''transport'' features from one space to another. Using this transport procedure we can show that the amplitude and phase calculations in the phase spaces for the two models are identical. The asymptotics of a complicated spin network, and thus the fundamental amplitudes of loop quantum gravity and spin-foam gravity, may be computed by first setting up an inner product remodeling and then picking and choosing which features of the calculation to perform in which space. </p><p> In this dissertation we first introduce the remodeling of an inner product and the semiclassical features of the remodeling. We then apply the remodeling to the well-studied cases of the 3<i>j</i>-symbol and the 6<i> j</i>-symbol. Finally we explore how the remodel procedure applies to more complicated spin networks such as the 15<i>j</i>-symbol and the <i>g</i>-inserted spin networks of loop quantum gravity.</p>

Following the holographic QCD model of Sakai and Sugimoto, we analyze the mesonic spectrum of a large N thermal QCD model in the dual string theory. After a T-dual transformation, the background of the ten-dimensional spacetime contains N D4-branes and $N_f$ D6/D6-branes and the internal manifold consists of a resolved-deformed conifold whose $\psi$ direction is the analogue of the compact cycle of the Sakai-Sugimoto's geometry. Using the probe approximation, we study the DBI action of the D6-branes and, by restricting the coordinate dependence of the ten-dimensional gauge flux components $A_M$, we recover a four-dimensional QCD-like action. In particular, this reduced action contains mass terms of vector mesons, which are related to the Minkowski components of the gauge flux. We calculate the values of these masses and our predictions find good agreement with the experimental values. / Inspiré par le modèle de mécanique chromodynamique (QCD) holographique de Sakai et Sugimoto, nous analysons, dans la limite où N est grand, le spectre mésonique d'un modèle de QCD à température finie à partir de la théorie des cordes correspondante. Après une transformation de dualité T, l'espace-temps de dix dimensions contient N D4-branes et $N_f$ D6/D6-branes et les dimensions enroulées consistent en une variété conique dont la dimension $\psi$ est l'analogue de la dimension enroulée de la géométrie de Sakai-Sugimoto. En utilisant l'approximation de sonde, nous étudions l'action DBI des D6-branes et, en restreignant la dépendance des composantes du flux de jauge $A_M$ de dix dimensions sur les coordonnées Minkowskiennes et $\psi$, nous retrouvons une action à quatre dimensions semblable à celle de QCD. Entre autres, cette action réduite contient des termes de masse de mésons vectoriels lesquels sont reliés aux composantes du flux de jauge. Nous calculons les valeurs de ces masses et nos prédictions sont comparables aux valeurs expérimentales.

We develop a mesoscopic theoretical framework to study viscoelastic response of block copolymers in the vicinity of their order-disorder transition point. We use it to study orientation selection of lamellar phases of diblock copolymers under oscillatory shears. We examine the effect of hydrodynamics on the relaxation of lamellar phases, and include anisotropic viscous stresses that follow from the uniaxial nature of the phase. We also introduce network viscoelastic effects that model chain entanglements, also made consistent with the symmetry of the phase. A numerical algorithm has been developed to solve the governing equations, which has been implemented on a parallel computer architecture. Simple cases involving the relaxation of small transverse perturbations, or viscoelasticity arising from diffusive relaxation of the order parameter have been investigated, and used to validate the numerical code. We also address the issue of spontaneous orientation selection from an initially disordered state due to an imposed oscillatory shear. In the absence of hydrodynamic coupling, we observe that the so called parallel orientation is selected for small shear frequency and amplitude, crossing over to a perpendicular orientation at higher shear frequencies and amplitudes. Hydrodynamic effects are seen to shift this crossover region. We have also examined the effect of network entanglement at finite frequencies. We find that network entanglement can lead to faster alignment, and that anisotropic network stresses can significantly influence the orientation selection process. / Nous developpons un cadre theorique propre a l'echelle me oscopique dans le but d'etudier la reponse viscoelastique des blocs de copolymeres pres du point de transition entre leur etat ordonne et desordonne. Nous utilisons cette theorie pour e tudier la selection de l'orientation des phases de lamelles des blocs de copolymeres subissant des cisaillements oscillatoires. Nous examinons les effets hydrodynamiques de la relaxation des phases lamellaires et nous incluons les stress visqueux anisotropes, dues a la nature uniaxiale des phases. Nous introduisons aussi les effets viscoelastique relatifs aux r eseaux modelisant l'enchevetrement des chaines dans une approche consistante avec la symetrie des phases. Un algorithme nume rique sous implementation parallele a ete developpe pour resoudre les equations relatives a cette etude. Des cas simples impliquant la relaxation diffuse du parametre relatif a l'ordre ont ete examines et utilises pour verifier le code numerique. Nous adressons aussi la question de la selection de l'orientation spontane d'un etat initialement desordonne due a un cisaillement oscillatoire impose au systeme. Dans l'absence d'interaction hydrodynamique, nous observons que l'orientation denomme e parallele est selectionnee pour des petites frequences et amplitudes de cisaillement mais adopte une orientation perpendiculaire pour de grandes frequences et amplitudes de cisaillement. Les effets hydrodynamiques changent la region de transition. Nous avons aussi examin e l'effet d'enchevetrement du reseau pour des frequences finies. Nous trouvons que l'enchevetrement du reseau mene a un alignement plus rapide et que les stress des reseaux anisotropes peuvent influencer de maniere significative le processus de se lection d'orientation.

In this thesis we study higher spin theories in three dimensional gravity with a negative cosmological constant based on the gauge group SL(N,R)xSL(N,R). First we introduce the topic of semi-classical gravity in three dimensional anti de Sitter space andits conjectured duality with a two dimensional conformal field theory. We study black hole solutions for the case of N=3 characterized by their holonomies around the non-contractible cycles of space-time. The black hole solutions are shown to be gauge equivalent to a BTZ black hole which is charged under a set of U(1) Chern-Simons fields. Nevertheless, depending on the choice of embedding of the gravitational gauge group, the space-time geometry may be non-trivial. We also investigate in detail the physical sensibility of non principal embeddings of the gravitational SL(2,R) in SL(N,R) and we conclude that theonly embedding with a positive definite spectrum is the principal one. / Cette thèse s'intéresse aux théories gravitationnelles couplées à des spins entiers avec une constante cosmologiquenégative, dont l'origine provient de l'étude du groupe de jauge sl_N. La gravitation dans l'espace tridimensionnel anti de Sitter est d'abord décrite de manière semi-classique et la dualité avec la théorie conforme de champs en deux dimensions est ensuite présentée. L'exposition des solutions de la théorie N=3 permet la caractérisation des trous noirs par les propriétés des holonomies autour de boucles non-contractiles. L'invariance de jauge rapproche alors ces solutions aux trous noirs BTZ avec une charge d'un champ Chern-Simons. Néanmoins, la géometrie de l'espace-temps dépend du plongement des symétries gravitationnelles SL(2,R) dans le groupe de jauge SL(N,R). Le spectre des solutions est calculé pour tous ces plongements, et la condition de positivité exclut alors tous les cas sauf le plongement principal.

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. / 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. / 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 &sim; 10-6 M4Planck . / 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. / 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 &sim; 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 &sim; (10-3eV)4 due to loops because the supersymmetry-breaking scale in the bulk is MSUSY &sim; r-1; although there remains a great deal of work to be done. We comment on recent extensions to cosmological backgrounds. / 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.