Foi analisada, através de simulação Monte Carlo, a probabilidade de que um gap de rapidez seja observado na produção do boson de Higgs por fusão de bosons vetoriais com massa (W), no LHC (Large Hadron Collider). Foi analisada, também através do uso de Monte Carlo, a possibilidade de que a existência ou não de um gap de rapidez seja usada na distinção de um Higgs produzido por fusão de bosons vetoriais W de outro produzido por fusão de gluons. Os diferentes modelos para tratamento de processos não perturbativos dos códigos Monte Carlo DTUJET e PYTHIA foram comparados. / The gap survival probability for a higgs boson produced by W fusion at the LHC (Large Hadron Collider) is analyzed through Monte Carlo simulation. The possibility of distinguishing between two higgs production mechanisms, W and gluon fusion is studied using Monte Carlo simulation. The two different models for non pertubative processes, used by DTUJET and PYTHIA are compared.

Foi analisada, através de simulação Monte Carlo, a probabilidade de que um gap de rapidez seja observado na produção do boson de Higgs por fusão de bosons vetoriais com massa (W), no LHC (Large Hadron Collider). Foi analisada, também através do uso de Monte Carlo, a possibilidade de que a existência ou não de um gap de rapidez seja usada na distinção de um Higgs produzido por fusão de bosons vetoriais W de outro produzido por fusão de gluons. Os diferentes modelos para tratamento de processos não perturbativos dos códigos Monte Carlo DTUJET e PYTHIA foram comparados. / The gap survival probability for a higgs boson produced by W fusion at the LHC (Large Hadron Collider) is analyzed through Monte Carlo simulation. The possibility of distinguishing between two higgs production mechanisms, W and gluon fusion is studied using Monte Carlo simulation. The two different models for non pertubative processes, used by DTUJET and PYTHIA are compared.

Large amplitude internal solitary waves in the coastal ocean are commonly modelled with the Korteweg-de Vries (KdV) equation or a closely related evolution equation. The characteristic feature of these models is the solitary wave solution, and it is well documented that these provide the basic paradigm for the interpretation of oceanic observations. However, often internal waves in the ocean survive for several inertial periods, and in that case, the KdV equation is supplemented with a linear non-local term representing the effects of background rotation, commonly called the Ostrovsky equation. This equation does not support solitary wave solutions, and instead a solitary-like initial condition collapses due to radiation of inertia-gravity waves, with instead the long-time outcome typically being an unsteady nonlinear wave packet. The KdV equation and the Ostrovsky equation are formulated on the assumption that only a single vertical mode is used. In this thesis we consider the situation when two vertical modes are used, due to a near-resonance between their respective linear long wave phase speeds. This phenomenon can be described by a pair of coupled Ostrovsky equations, which is derived asymptotically from the full set of Euler equations and solved numerically using a pseudo-spectral method. The derivation of a system of coupled Ostrovsky equations is an important extension of coupled KdV equations on the one hand, and a single Ostrovsky equation on the other hand. The analytic structure and dynamical behaviour of the system have been elucidated in two main cases. The first case is when there is no background shear flow, while the second case is when the background state contains current shear, and both cases lead to new solution types with rich dynamical behaviour. We demonstrate that solitary-like initial conditions typically collapse into two unsteady nonlinear wave packets, propagating with distinct speeds corresponding to the extremum value in the group velocities. However, a background shear flow allows for several types of dynamical behaviour, supporting both unsteady and steady nonlinear wave packets, propagating with the speeds which can be predicted from the linear dispersion relation. In addition, in some cases secondary wave packets are formed associated with certain resonances which also can be identified from the linear dispersion relation. Finally, as a by-product of this study it was shown that a background shear flow can lead to the anomalous version of the single Ostrovsky equation, which supports a steady wave packet.

Cette thèse présente la conception et l'implémentation d'une nouvelle génération de puces à atomes, ouvrant de nouvelles perspectives expérimentales dans des micropièges magnétiques très anisotropes. Les propriétés thermiques des puces en nitrure d'aluminium sont étudiées en détail. Le dispositif a été optimisé pour piéger de plus grands nombres d'atomes et améliorer la qualité de l'imagerie, notamment en fabriquant un miroir de planéité sub-λ/10 à la surface de la puce.Nous étudions des gaz quasi-1D grâce à des images in situ de profils fluctuants et des méthodes précises de calibration et d'analyse statistique. Nous mesurons des fluctuations non-gaussiennes, ce qui permet de tester sensiblement la thermodynamique du gaz et donne une mesure de corrélations à trois corps. Nous étudions précisément la transition de quasicondensation et mesurons pour la première fois sa loi d'échelle. En régime 3D, c'est une condensation transverse qui déclenche la quasicondensation longitudinale, tandis qu'en régime 1D, la formation d'un quasicondensat est gouvernée par les interactions répulsives et non par la dégénérescence quantique.Obtenant des températures record pour des gaz 1D, nous observons des fluctuations subpoissoniennes lorsque les corrélations atomiques sont déterminées, au moins localement, par les fluctuations quantiques qui dominent les fluctuations thermiques. Nous discutons également la thermalisation étonnamment rapide mesurée en régime 1D profond qui suggère que des collisions effectives à 3 corps brisent l'intégrabilité du système. / This thesis presents the design and implementation of a new generation of atom chips, that open novel experimental possibilities with very anisotropic magnetic microtraps. The thermal properties of aluminum nitride atom chips are studied in detail. We have optimized the set-up in order to trap more atoms and image the clouds as precisely as possible. In particular we have fabricated a miror of sub-λ/10 planeity on top of the chip surface.We study quasi-1D gases using in situ pictures of the fluctuating density pro_les and precise methods for their calibration and statistical analysis. We measure non-gaussian fluctuations, which provides a sensitive test of the thermodynamics of the system and gives a measure of three-body correlations. We study precisely the quasicondensation transition, measuring its scaling for the first time. In the 3D regime, a transverse condensation triggers the longitudinal quasicondensation. In the 1D regime, on the contrary, the appearance of a quasicondensate is governed by repulsive interactions only, and not by quantum degeneracy.Reaching record temperatures for 1D gases, we observe subpoissonian fluctuations which indicate that atomic correlations are determined at least locally by quantum rather than thermal fluctuations. We also discuss our observation of surprizingly e_fficient thermalization deep in the 1D regime, suggesting that e_ffective 3-body collisions break the integrability of the system.

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