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Search for diphoton resonances in the mass range from 150 to 850 GeV in pp collisions at sqrt(s) = 8 TeV
No full textsee paper for full list of authorsInternational audienceResults are presented of a search for heavy particles decaying into two photons. The analysis is based on a 19.7 inverse femtobarn sample of proton-proton collisions at sqrt(s) = 8 TeV collected with the CMS detector at the CERN LHC. The diphoton mass spectrum from 150 to 850 GeV is used to search for an excess of events over the background. The search is extended to new resonances with natural widths of up to 10% of the mass value. No evidence for new particle production is observed and limits at 95% confidence level on the production cross section times branching fraction to diphotons are determined. These limits are interpreted in terms of two-Higgs-doublet model parameters
Feynman-Kac representation for Hamilton-Jacobi-Bellman IPDE
No full text38 pagesWe aim to provide a Feynman-Kac type representation for Hamilton-Jacobi-Bellman equation, in terms of Forward Backward Stochastic Differential Equation (FBSDE) with a simulatable forward process. For this purpose, we introduce a class of BSDE where the jumps component of the solution is subject to a partial nonpositive constraint. Existence and approximation of a unique minimal solution is proved by a penalization method under mild assumptions. We then show how minimal solution to this BSDE class provides a new probabilistic representation for nonlinear integro-partial differential equations (IPDEs) of Hamilton-Jacobi-Bellman (HJB) type, when considering a regime switching forward SDE in a Markovian framework. Moreover, we state a dual formula of this BSDE minimal solution involving equivalent change of probability measures. This gives in particular an original representation for value functions of stochastic control problems including controlled diffusion coefficient
Pre-processing for approximate Bayesian computation in image analysis
No full text5th IMS-ISBA joint meeting (MCMSki IV)International audienceMost of the existing algorithms for approximate Bayesian computation (ABC) assume that it is feasible to simulate pseudo-data from the model at each iteration. However, the computational cost of these simulations can be prohibitive for high dimensional data. An important example is the Potts model, which is commonly used in image analysis. Images encountered in real world applications can have millions of pixels, therefore scalability is a major concern. We apply ABC with a synthetic likelihood to the hidden Potts model with additive Gaussian noise. Using a pre-processing step, we fit a binding function to model the relationship between the model parameters and the synthetic likelihood parameters. Our numerical experiments demonstrate that the precomputed binding function dramatically improves the scalability of ABC, reducing the average runtime required for model fitting from 71 hours to only 7 minutes. We also illustrate the method by estimating the smoothing parameter for remotely sensed satellite imagery. Without precomputation, Bayesian inference is impractical for datasets of that scale
Stability in the energy space for chains of solitons of the Landau-Lifshitz equation
No full textInternational audienceWe prove the orbital stability of sums of solitons for the one-dimensional Landau-Lifshitz equation with an easy-plane anisotropy, under the assumptions that the (non-zero) speeds of the solitons are different, and that their initial positions are sufficiently separated and ordered according to their speeds
Search for dark matter, extra dimensions, and unparticles in monojet events in proton-proton collisions at sqrt(s) = 8 TeV
No full textSubmitted to Eur. Phys. J. C, see paper for full list of authorsResults are presented from a search for particle dark matter (DM), extra dimensions, and unparticles using events containing a jet and an imbalance in transverse momentum. The data were collected by the CMS detector in proton-proton collisions at the LHC and correspond to an integrated luminosity of 19.7 inverse femtobarns at a centre-of-mass energy of 8 TeV. The number of observed events is found to be consistent with the standard model prediction. Limits are placed on the DM-nucleon scattering cross section as a function of the DM particle mass for spin-dependent and spin-independent interactions. Limits are also placed on the scale parameter M[D] in the ADD model of large extra dimensions, and on the unparticle model parameter Lambda[U]. The constraints on ADD models and unparticles are the most stringent limits in this channel and those on the DM-nucleon scattering cross section are an improvement over previous collider results
Search for quark contact interactions and extra spatial dimensions using dijet angular distributions in proton-proton collisions at sqrt(s) = 8 TeV
No full textSubmitted to Phys. Lett. B ; see paper for full list of authorsInternational audienceA search is presented for quark contact interactions and extra spatial dimensions in proton-proton collisions at sqrt(s) = 8 TeV using dijet angular distributions. The search is based on a data set corresponding to an integrated luminosity of 19.7 inverse femtobarns collected by the CMS detector at the CERN LHC. Dijet angular distributions are found to be in agreement with the perturbative QCD predictions that include electroweak corrections. Limits on the contact interaction scale from a variety of models at next-to-leading order in QCD corrections are obtained. A benchmark model in which only left-handed quarks participate is excluded up to a scale of 9.0 (11.7) TeV for destructive (constructive) interference at 95% confidence level. Lower limits between 6.0 and 8.4 TeV on the scale of virtual graviton exchange are extracted for the Arkani-Hamed--Dimopoulos--Dvali model of extra spatial dimensions
Regional mesoscale air-sea coupling impacts and extreme meteorological events role on the Mediterranean Sea water budget
No full textInternational audienceThe Mediterranean Sea water budget (MWB) is a key parameter, as it controls the Mediterranean Sea water loss and thus the Atlantic Water inflow and the Mediterranean general circulation. More accurately, the MWB controls the net flow through the Strait of Gibraltar, which implies both inflow and outflow. Generally considered at the basin scale and over long-term periods, the MWB is in fact characterized by a large variability in space and time, induced by the complex topography of the region, mesoscale processes and (short) intense events in the ocean and atmosphere compartments. In this study, we use an ocean-atmosphere coupled system at mesoscale able to represent such phenomena, to evaluate the MWB atmospheric components: Evaporation (E) and Precipitation (P). We compare two companion regional simulations: an uncoupled atmospheric run using the ERA-interim Sea Surface Temperature (SST) reanalysis and a coupled run using the MORCE system with the two-way coupling between the NEMO-MED12 eddy-resolving ocean model and the non-hydrostatic Weather Research and Forecasting atmospheric model. We first evaluate the SST validity against satellite data and evidence the coupled system ability in representing SST mesoscale structures, characteristics of the Mediterranean circulation and of small-scale ocean processes, despite a colder mean value and a lower amplitude of the annual cycle. Then, the comparison aims to examine the coupled processes effects (meaning the impacts of the interactive high-resolution and high-frequency SST) on E and P and on their variability. The comparison highlights that the SST is the controlling factor for E and P budgets, with reduction by 6 and 3 % in the coupled run compared to the uncoupled run, respectively. The modifications propagate until 750 km inland far from the Mediterranean coast, as towards the Atlantic Ocean and the Black Sea. This indicates that coupling plays a major role in distributing water at mesoscale. The coupling directly modifies the seasonal variability. It also significantly decreases extreme evaporation and precipitation occurences and intensities. This extreme events mitigation in the coupled run contributes for ~50 % to the decrease in the E and P budgets
Energy release rate for non smooth cracks in planar elasticity
No full textThis paper is devoted to the characterization of the energy release rate of a crack which is merely closed, connected, and with density at the tip. First, the blow-up limit of the displacement is analyzed, and the convergence to the corresponding positively -homogenous function in the cracked plane is established. Then, the energy release rate is obtained as the derivative of the elastic energy with respect to an infinitesimal additional crack increment
Transport dépendant du spin dans les semi-conducteurs: une conséquence du principe de Pauli.
No full textThis thesis is concerned with transport of photoinjected minority spin-polarized electrons in doped semiconductors, as a function of both the density and the temperature of the injected electron gas. In p-GaAs thin films, charge and spin transport is investigated theoretically and experimentally by using a novel polarized microphotoluminescence (µPL) technique which consists in imaging the spatially-resolved PL intensity and polarization under a tightly-focused circularly-polarized CW laser excitation. Study of the experimental profiles at low concentration and under an applied electric field shows that the minority electron mobility is mainly determined by the electron temperature instead of the majority hole statistics, introducing a puzzling piece to the current understanding of scattering processes in semiconductors. At higher densities, this experimental technique has allowed us to explore a novel charge-spin coupling mechanism which modifies electron transport. Under degeneracy of the electron gas (high concentration, low temperature), a dip at the centre of the spin polarization profile appears with a polarization maximum at a distance of about r= 2 µm from the excitation. This counterintuitive result reveals that photoelectron diffusion depends on spin, as a direct consequence of the Pauli principle which causes in general a concentration dependence of the spin stiffness. This results in a novel spin filter effect in an homogeneous material. The other effects which may modify spin transport in a degenerate electron gas are thermoelectric spin currrents (spin Soret currents) and ambipolar coupling with holes. A comparison of the data with a numerical solution of the coupled diffusion equations reveals that ambipolar diffusion increases the steady-state photo-electron density at the centre and therefore the amplitude of the degeneracy-induced spin-dependent diffusion, while the contribution of the spin Soret current is negligible. Coulomb spin drag and bandgap renormalization are negligible due to electrostatic screening by the hole gas. It is expected for degeneracy to have larger effects in confined systems, such as quantum wells, where both the spin stiffness and the mobility can have a much strong spin dependence.Ce travail de thèse est consacré à l'étude du transport des électrons minoritaires dans des semi-conducteurs dopés, en fonction de la densité et de la température du gaz électronique. Dans des couches minces de p-GaAs, le transport de la charge et du spin est étudié par un approche à la fois théorique et expérimental en utilisant une technique de microscopie originale permettant d'imager en régime stationnaire le profil de charge et de spin en fonction de la distance r par rapport à la tache d'excitation lumineuse. L'étude de ces profils a faible concentration et sous l'application d'un champ électrique montre que la mobilité des électrons minoritaires est déterminée principalement par la température des électrons et non pas par la statistique des trous majoritaires, ce qui invite a reformuler les modèles théoriques concernant les processus de diffusion des porteurs minoritaires dans les semi-conducteurs. Notre technique expérimentale a aussi permis d'explorer un nouveau mécanisme de couplage charge-spin lorsque la densité électronique est élevée. En effet, sous l'effet de la dégénérescence du gaz électronique (forte concentration, basse température), une diminution de la polarisation de spin à l'endroit d'excitation apparaît, avec un maximum de polarisation visible à environ r=2 µm. Ce résultat contra intuitif révèle le fait que, à cause du principe de Pauli, la diffusion des photo-électrons dépend du spin, car la raideur de spin devient une fonction de la concentration dans le régime dégénéré. Un nouveau mécanisme de filtre à spin en découle, mais qui ne fait pas intervenir une interface entre deux matériaux. D'autres effets pouvant modifier le transport de spin dans le régime dégénéré sont les courants thermoélectriques de spin (courants de Soret) et le couplage ambipolaire avec les trous. Une comparaison entre les profils expérimentaux et une solution numérique des équations de diffusion couplées montre que le couplage ambipolaire augmente la concentration de photo-électrons dans le régime stationnaire, et donc l'amplitude des effets liées à la dégénérescence, tandis que les courants de Soret de spin sont négligleables. Des effets tels que la renormalisation du gap et le couplage Coulombien entre électrons de spin opposés sont aussi négligeables à cause de l'écrantage des intéractions électron-électron induit par le gaz électronique. On s'attend à que l'effet de la dégénérescence augmente dans des systèmes confinés, tels que les puits quantiques, où la raideur de spin et la mobilité peuvent avoir des dépendances en spin encore plus fortes