In this thesis we study second-order relativistic hydrodynamics particularly in the context of quantum field theory and AdS/CFT. The theory of hydrodynamics can be thought of as an effective theory in derivative expansion. At first order in derivatives, the result is the equations of motion generally known as the Navier-Stokes equations. But the relativistic Navier-Stokes equations are acausal and numerically unstable. The solution was to extend the derivative expansion to second order. With this generalization we can have more terms with independent coefficients. The main method to obtain information and formally define these viscosities is to derive a set of Kubo formulae for each of these parameters. Kubo formulae are defined in terms of the limit of zero frequency and momentum of the correlation functions of currents or energy-momentum tensors. At first-order hydrodynamics, they are written in terms of two-point functions. We showed that at second order they are defined by generalized three-point Green's functions. Along the way in this thesis, we show that in general, properties of hydrodynamic systems can be classified as thermodynamical and dynamical. Based on the recent and ongoing experiments from RHIC (Relativistic Heavy Ion Collider) and the LHC (Large Hadron Collider), the relevance of these effects are shown. A through examination of the thermodynamical parameters is given in perturbative quantum field theory, non-perturbative lattice field theory and also in the AdS/CFT context. We give a complete calculation of thermodynamical parameters for a generic free field theory and study the coupling power of different orders of perturbation. Using the AdS/CFT correspondence, we calculate them again in the limit of infinite t'Hooft coupling; furthermore the effect of next-to-leading-order terms will be addressed. Since they haven't been computed using lattice field theory techniques, we develop a general picture for the calculation of these Euclidean transport parameters. Next, we show that one of the primary dynamical features of viscosities are the presence of long-time tails. These tails in 3 + 1 dimensions exhibit certain diffusional effects on momentum density and they will give corrections to viscosities. We also clarify the non-linear nature of the outcome. We hope that this thesis sheds light on nature of the matter produced in RHIC and the LHC. / Dans cette thèse, nous étudions l'hydrodynamique relativiste de second ordre en mettant un accent particulier sur sa relation avec la théorie des champs quantiques et l'AdS/CFT. La théorie de l'hydrodynamique peut etre vue comme la théorie efficace d'une expansion en gradients d'une autre théorie. Au premier ordre de cette expansion en gradients, les équations du mouvement de cette théorie efficace correspondent aux équations de Navier-Stokes. Il est cependent connu que la version relativiste des équations de Navier-Stokes n'est ni causale, ni stable numériquement. L'approche utilisée pour corriger ce problème est d'aller à l'ordre supérieur, le second ordre, de l'expansion en gradients. Cette généralisation introduit de nouveaux degrées de libertées, et donc de nouveaux paramètres de transport. La principale méthode pour obtenir de l'information sur ces paramètres est de dériver un ensemble de formules de Kubo pour chacun de ces paramètres. Ces formules sont définies en fonction de la limite zéro fréquence et impulsion de fonctions de corrélations de courants ou de tenseurs d'energie-impulsion. Pour la théorie hydrodynamique au premier ordre, leur expressions prennent la forme de fonctions à deux points. Nous montrons qu'au second ordre, ces formules sont définies comme comme des fonctions de Green généralisées à trois points. Plus spécifiquement, nous montrons dans cette thèse qu'en général, les propriétés de systèmes hydrodynamiques peuvent etre classifiées en propriétés soient dynamiques, soient thermodynamiques. À l'aide des expériences ayant présentement lieu au RHIC (Relativistic Heavy Ion Collider) et au LHC (Large Hadron Collider), l'importance de ces effets est démontrée. Un examen approfondi des paramètres thermodynamiques est donné en théorie des champs perturbatives, en théorie des champs sur réseaux, ainsi qu'en AdS/CFT. Nous donnons un calcul complet des paramètres thermodynamiques pour le cas générique d'un champ libre, et discutons des effets des corrections perturbatives d'ordres supérieurs. En utilisant la correspondance AdS/CFT, nous calculons à nouveau ces coefficients dans la limite d'un couplage de t'Hooft infini, en commentant sur l'effet de l'ordre supérieur sur le calcul. Une approche générale pour le calcul de ces paramètres de transport euclidiens est d'eveloppée pour pallier l'absence de tels résultats dans l'approche des champs sur réseaux. Ensuite, nous démontrons que l'une des principales caractéristiques dynamiques des viscosités est la présence de longues queues temporelles. En 3+1 dimensions, ces queues montrent certains effets de diffusions sur la densité d'impulsion, et elles apportent des corrections aux coefficients. Nous clarifions la nature non-linéaire du résultat. Nous espèrons que cette thèse contribuera à élucider la nature de la matière produite au RHIC et au LHC.

No description available.

This thesis describes an experimental investigation of semileptonic B meson decays with a D and pi mesons in the final state: B- &rarr; D+pi -e-nu e. The data for the analysis were collected with the CLEO II detector at the Cornell Electron-positron Storage Ring. The D meson is reconstructed in the D+ &rarr; K-pi+pi+ channel. The advantage of using this particular B decay mode is that there is no contribution from the D* due to phase space exclusion. This analysis is the first attempt at measuring non-resonant decays semileptonic decays with the CLEO II detector. Even though we do not distinguish between higher order D resonances and the so called non-resonant decays, measuring this decay channel reveals useful information about the deficit observed in inclusive charm semileptonic B decays. We present the full neutrino reconstruction method used in extracting this decay channel from our data sample. The main difficulty comes in understanding combinatoric backgrounds and we develop two methods to solve this problem. After extensive study, no statistically significant signal is observed. So an upper limit is extracted. The result we obtain is B (B- &rarr; D +pi-e- nue) < 0.71% at 90% C.L. This is consistent with the expected amount of B - &rarr; D+pi- e-nu e events predicted by the current models.

Recent developments in string theory have led to the understanding that many physical systems posses multiple equivalent, or dual, descriptions which are distinguished by their usefulness in differing regions of parameter space. Dualities of this type often relate theories which exist in different numbers of space-time dimensions and it is the purpose of this thesis to examine several examples of this phenomenon. It is well known that the low energy dynamics of D3-branes is well described by N = 4 super-Yang-Mills theory in 3 + 1 dimensions. In the first part of this thesis it will be shown how the physics of magnetic monopole solutions of this theory is often best described by a 1 + 1 dimensional quantum field theory. In particular it is found that near the core of the monopole the most appropriate description of the physics is in terms of a particular version of non-commutative geometry arising from the non-abelian nature of the 1 + 1 dimensional field theory. The second part of this thesis discusses the duality between Anti de-Sitter Space and Conformal Field Theory (the AdS/CFT correspondence) which states that at strong coupling N = 4 Super-Yang-Mills theory is actually best described by type IIB superstring theory in 9 + 1 dimensions. The implications of this conjecture as applied to non-supersymmetric field theories are explored and it is found that many properties of quantum-chromo-dynamics (QCD) such as confinement and mass gaps can effectively be studied using string theory techniques. It is also shown how the mass spectra of glueballs in QCD-like theories can be computed. These techniques are then turned around to deduce from the field theory a perturbative proof of a positive energy conjecture for asymptotically AdS spaces.

In this thesis, a method for calculating the decay rates and branching ratios using perturbative QCD and QED is proposed. Among the assumptions used are that heavy mesons are non-relativistic quark/anti-quark bound states and that light mesons can be treated as quarks in a bag. The method will be applied to the $ eta sb{c} to phi phi$ decay and to 1-loop contributions to the leptonic widths of mesons.

<p> Experimental high energy physics (HEP) techniques are applied to accurate simulated collider data in search for existence or exclusion of supersymmetric (SUSY) particles. Supersymmetry is a leading candidate to resolve the hierarchy problem in particle physics as well as offer a stable dark matter candidate. Techniques and practices are explored and applied to the leptonic decay process production followed by and where is the proton, is the chargino, , are neutralinos and , are the standard model W and Higgs Bosons respectively. Signal yields are in general agreement with other researchers and ranged from 0.5 to 62.6 events. Reduction in the background to signal ratio is demonstrated through isolating the SUSY process and applying theoretical knowledge of the signal and associated dominant backgrounds. Results from this study establish procedures for future work with actual data, offer a benchmark for this specific leptonic decay process and may motivate variable selection and cut criteria choices in future analysis of similar signal processes.</p>

Cosmic strings are linear concentrations of energy of macroscopic size. Cosmic superstrings come from string theory and can form junctions. In the introduction, we define more precisely the strings, their formation and the main properties of single straight cosmic strings or superstrings. Then, we focus on those latter and study some major properties of junctions. As a first step, we find the metric close to a junction of strings in the weak-field approximation. We then find some signatures that would reveal their presence : Namely, the lensing that they create and the shift in photon wavelength passing through (leading to the Kaiser-Stebbins effect) in chapter 2, and the gravitational radiation they can emit in chapter 3. / Les supercordes cosmiques correspondent a des concentrations linaires d'energieemprisonnee de taille macroscopique. Les supercordes cosmiques, sont celles resultant de la theorie des cordes et peuvent former des jonctions. L'introduction definit plus precisement les cordes, leur formation et les principales proprietes des cordes ou des supercordes droites. Ensuite, on se focalise sur ces dernieres en etudiant les principales proprietes des jonctions. Un premier pas consiste a trouver la metrique proched'une jonction de cordes dans l'approximation de champ faible. Ensuite on trouverades possibles signatures qui reveleraient leur presence : L'effet de lentilles qu'ellescreent et le decalage dans la longueur d'onde des photons passant aux alentours(ce qui mene a l'effet Kaiser-Stebbins) au chapitre 2, et la radiation gravitationellequ'elles peuvent emettre au chapitre 3.

In ultra-relativistic heavy ion collisions, the centrality of a collision is measured by the total charged particle multiplicity while the distribution of these particles in rapidity space is a reflection of the thermodynamical conditions and the hadronization processes in the collision volume. As one of the R & D projects for the PHENIX experiment at RHIC, a double-sided Si $p sp+nn sp+$ junction pad detector is developed. One side of the detector measures the particle distribution and the other side the total multiplicity. A prototype detector made of 7.6 cm diameter, 300 $ mu$m thick Si wafer with 512 pads on one side and 16 larger pads (petals) on the opposite side has been successfully developed, constructed and tested, both in-beam and off-beam at the Brookhaven National Laboratory. The detector, the results as well as the Monte-Carlo simulation comparisons are presented.

We present a study of the properties of the nuclear matter under extreme conditions of density and temperature, using collisions of heavy-nuclei measured in the experiment NA34. The emphasis is given to the study of the variation of the properties of average central collisions with the sizes of the colliding nuclei. The projectiles used are 200 GeV protons, 60 and 200 GeV/nucleon $ sp{16}$O nuclei, and 200 GeV/nucleon $ sp{32}$S nuclei. The targets are thin disks of aluminium, copper, silver, tungsten, platinum, lead and uranium nuclei. The energy density achieved in these collisions, of the order of 10 GeV/fm$ sp3$, is a necessary (but not sufficient) condition to create a plasma of quarks and gluons. We investigate whether an hydrodynamic description is appropriate for our data, in which case, from the observation of the work done by the hydrodynamic forces, constraints are obtained on the properties of the hypothetical plasma.

The photoproduction of D+/-s mesons has been measured with the ZEUS detector at HERA. The data sample corresponds to an integrated luminosity of 121.6 pb-1 . The total and differential cross-sections as functions of the Ds transverse momentum, pseudorapidity and photon-proton center-of-mass energy are measured for 3 < pt( Ds) < 12 GeV, |eta(Ds)| < 1.5 and 130 < W < 280 GeV. The total measured cross-section is sep→DsX = 3.869+/-0.286+0.134-0.150 nb. The measurements are compared with leading-order Monte Carlo simulations as well as next-to-leading order perturbative QCD calculations. / The ratio of D+/-s to D*+/- mesons cross-sections was used to measure the strangeness suppression factor gamma s within the Lund string fragmentation model. Using PYTHIA and CASCADE Monte Carlo simulations, the obtained values are gamma s = 0.281+/-0.205+0.0096-0.0116 and gammas = 0.263+/-0.0189+0.0081-0.0133 , respectively, which are in good agreement with previous measurements and with e+e- annihilations.