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Comparison of real-time refractivity measurements by radar with automatic weather stations, AROME-WMED and WRF forecast simulations during SOP1 of the HyMeX campaign
No full textInternational audienceWeather radars, originally designed to detect and quantify precipitation, can be used to estimate and map the refractivity at low level, a proxy for humidity. As highlighted by previous studies, this presents a definite meteorological interest, both for numerical weather prediction and for atmospheric process studies. Recent works have given keys to perform high-accuracy measurements over operational radar without decreasing the quality of reflectivity and Doppler wind classical measurements, and the retrieval of radar refractivity is now performed in real time with the Météo-France ARAMIS (Application Radar à la Météorologie Infra-Synoptique) operational network.Taking advantage of the Hydrological cycle in Mediterranean eXperiment (HyMeX) field campaign (September-November 2012), refractivity measured by a few radars located in South-East France has been compared with in-situ measurement by Automatic Weather Stations (AWSs), and correlation between these two independent observations is quite good, in particular with a high quality of the diurnal cycle and during the pre-convection period measurement by the radar.To go further in the evaluation of the usefulness of such product, we compared refractivity derived from radar measurements and from two different kinds of models: the numerical prediction model Applications de la Recherche à l'Opérationnel à Méso-Echelle – Western MEDiterranean (AROME-WMED) using a 2.5 km resolution grid mesh over southern France and a coarser resolution simulation (54x54 km) performed with the Weather Research and Forecasting (WRF) model which both ran in a forecasting mode during the HYMEX Special Observing Period 1. These two models give access to the variability of the modeling and thus enable to quantify the uncertainty of the refractivity modeling. The result of this comparison is generally fairly good, with a pattern of refractivity field similar to observations (AWS and radar), although obviously with locally strong differences.We finally illustrate the usefulness of refractivity mapping by radar by investigating a typical meteorological situation of a convective system observed during the HyMeX campaign
Bifurcation of magnetic island saturation controlled by plasma viscosity
No full textInternational audienceTwo nonlinear regimes, depending on the magnetic Prandtl number Prm, are identified for magnetic islands described by resistive MHD equations. The frontier between these two regimes is sharp, and has the characteristics of a phase transition controlled by plasma viscosity. In the low Prm regime, a new form of the so-called flip instability, consisting of a sudden change of the island phase, is identified. Already known in the context of a forcing by external magnetic perturbations and localized current drive, it occurs spontaneously at low Prm. The main characteristics of this new structural instability are described. The low Prm regime is well described by the slab visco-resistive model in the linear phase, and is characterized by both a large saturation of the island and strong nonlinearly driven zonal flows (that do not impact significantly the island dynamics however), while curvature physics strongly impacts the viscous regime
Search for new physics with the MT2 variable in all-jets final states produced in pp collisions at sqrt(s) = 13 TeV
No full textSubmitted to JHEP ; see paper for full list of authorsInternational audienceA search for new physics is performed using events that contain one or more jets, no isolated leptons, and a large transverse momentum imbalance, as measured through the MT2 variable, which is an extension of the transverse mass in events with two invisible particles. The results are based on a sample of proton-proton collisions collected at a center-of-mass energy of 13 TeV with the CMS detector at the LHC, and that corresponds to an integrated luminosity of 2.3 inverse femtobarns. The observed event yields in the data are consistent with predictions for the standard model backgrounds. The results are interpreted using simplified models of supersymmetry and are expressed in terms of limits on the masses of potential new colored particles. Assuming that the lightest neutralino is stable and has a mass less than about 500 GeV, gluino masses up to 1550-1750 GeV are excluded at 95% confidence level, depending on the gluino decay mechanism. For the scenario of direct production of squark-antisquark pairs, top squarks with masses up to 800 GeV are excluded, assuming a 100% branching fraction for the decay to a top quark and neutralino. Similarly, bottom squark masses are excluded up to 880 GeV, and masses of light-flavor squarks are excluded up to 600-1260 GeV, depending on the degree of degeneracy of the squark masses
Y(nS) polarizations versus particle multiplicity in pp collisions at sqrt(s) = 7 TeV
No full textSubmitted to Phys. Lett. B ; see paper for full list of authorsInternational audienceThe polarizations of the Y(1S), Y(2S), and Y(3S) mesons are measured as a function of the charged particle multiplicity in proton-proton collisions at sqrt(s) = 7 TeV. The measurements are performed with a dimuon data sample collected in 2011 by the CMS experiment, corresponding to an integrated luminosity of 4.9 inverse femtobarns. The results are extracted from the dimuon decay angular distributions, in two ranges of Y(nS) transverse momentum (10-15 and 15-35 GeV), and in the rapidity interval abs(y)<1.2. The results do not show significant changes from low- to high-multiplicity pp collisions, although large uncertainties preclude definite statements in the Y(2S) and Y(3S) cases
Search for s channel single top quark production in pp collisions at sqrt(s) = 7 and 8 TeV
No full textSubmitted to JHEP ; see paper for full list of authorsInternational audienceA search is presented for single top quark production in the s channel in proton-proton collisions with the CMS detector at the CERN LHC in decay modes of the top quark containing a muon or an electron in the final state. The signal is extracted through a maximum-likelihood fit to the distribution of a multivariate discriminant defined using boosted decision trees to separate the expected signal contribution from background processes. Data collected at centre-of-mass energies of 7 and 8 TeV yield cross sections of 7.1 +/- 8.1 pb and 13.4 +/- 7.3 pb, respectively, and a best fit value of 2.0 +/- 0.9 for the combined ratio of the measured and expected values. The signal significance is 2.5 standard deviations, and the upper limit on the rate relative to the standard model expectation is 4.7 at 95% confidence level
On magnetic monopoles, the anomalous g-factor of the electron and the spin-orbit coupling in the Dirac Theory
No full text38 pagesWe discuss the algebra and the interpretation of the anomalous Zeeman effect and the spin-orbit coupling within the Dirac theory. Whereas the algebra for the anomalous Zeeman effect is impeccable and therefore in excellent agreement with experiment, the physical interpretation of that algebra uses images that are based on macroscopic intuition but do not correspond to the meaning of this algebra. The interpretation violates the Lorentz symmetry. We therefore reconsider the interpretation to see if we can render it consistent also with the symmetry. The results confirm clearly that the traditional physical interpretation of the anomalous Zeeman effect is not correct. We give an alternative intuitive description of the meaning of this effect, which respects the symmetry and is exact. It can be summarized by stating that a magnetic field makes any charged particle spin. This is even true for charged particles " without spin ". Particles " with spin " acquire additional spin in a magnetic field. This additional spin must be combined algebraically with the pre-existing spin. We show also that the traditional discussion about magnetic monopoles confuses two issues, viz. the symmetry of the Maxwell equations and the quantization of charge. These two issues define each a different concept of magnetic monopole. They cannot be merged together into a unique all-encompassing issue. We also generalize the minimal substitution for a charged particle, and provide some intuition for the magnetic vector potential. We finally explore the algebra of the spin-orbit coupling, which turns out to be badly wrong. The traditional theory that is claimed to reproduce the Thomas half is based on a number of errors. An error-free application of the Dirac theory cannot account for the Thomas precession, because it only accounts for the instantaneous local boosts, not for the rotational component of the Lorentz transformation. This runs contrary to established beliefs, but can be understood in terms of the Berry phase on a path through the Lorentz group manifold. These results clearly reveal the limitations of the prevailing working philosophy to " shut up and calculate "
Counting, generating and sampling tree alignments
No full textInternational audiencePairwise ordered tree alignment are combinatorial objects that appear in RNA secondary structure comparison. However, the usual representation of tree alignments as supertrees is ambiguous, i.e. two distinct supertrees may induce identical sets of matches between identical pairs of trees. This ambiguity is uninformative, and detrimental to any probabilistic analysis.In this work, we consider tree alignments up to equivalence. Our first result is a precise asymptotic enumeration of tree alignments, obtained from a context-free grammar by mean of basic analytic combinatorics. Our second result focuses on alignments between two given ordered trees and . By refining our grammar to align specific trees, we obtain a decomposition scheme for the space of alignments, and use it to design an efficient dynamic programming algorithm for sampling alignments under the Gibbs-Boltzmann probability distribution. This generalizes existing tree alignment algorithms, and opens the door for a probabilistic analysis of the space of suboptimal RNA secondary structures alignments
TRIQS/CTHYB: A continuous-time quantum Monte Carlo hybridization expansion solver for quantum impurity problems
No full textInternational audienceWe present TRIQS/CTHYB, a state-of-the art open-source implementation of the continuous-time hybridisation expansion quantum impurity solver of the TRIQS package. This code is mainly designed to be used with the TRIQS library in order to solve the self-consistent quantum impurity problem in a multi-orbital dynamical mean field theory approach to strongly-correlated electrons, in particular in the context of realistic calculations. It is implemented in C++ for efficiency and is provided with a high-level Python interface. The code is ships with a new partitioning algorithm that divides the local Hilbert space without any user knowledge of the symmetries and quantum numbers of the Hamilto-nian. Furthermore, we implement higher-order configuration moves and show that such moves are necessary to ensure ergodicity of the Monte Carlo in common Hamiltonians even without symmetry-breaking
Self-organized arrays of dislocations in thin smectic liquid crystal films
No full textInternational audienceCombining optical microscopy, synchrotron X-ray diffraction and ellipsometry, we studied the internal structure of linear defect domains (oily streaks) in films of smectic liquid crystal 8CB with thickness 100-300 nm confined between air and a rubbed PVA polymer substrate which impose hybrid anchoring conditions (normal and unidirectional planar, respectively). We show how the presence or absence of dislocations control the structure of highly deformed thin smectic films. Each domain contains smectic layers curved in the shape of flattened hemicylinders to satisfy both anchoring conditions, together with grain boundaries whose size and shape are controlled by the presence of dislocation lines. A flat grain boundary normal to the interface connects neighboring hemicylinders, while a rotating grain boundary (RGB) is located near the axis of curvature of the cylinders. The RGB shape appears such that dislocation lines are concentrated at its summit close to the air interface. The smectic layers reach the polymer substrate via a transition region where the smectic layer orientation satisfies the planar anchoring condition over the entire polymer substrate and whose thickness does not depend on the one of the film. The strength of the planar anchoring appears to be high, larger than 10 −2 J/m 2 , compensating for the high energy cost of creating an additional 2D defect between an horizontal smectic layer and perpendicular ones. This 2D defect may be melted, in order to avoid the creation of a transition region structure composed of a large number of dislocations. As a result, linear defect domains can be considered as arrays of oriented defects, straight dislocations of various Burger vectors, whose location is now known and 2D nematic defects. The possibility of easy variation between the present structure with a moderate amount of dislocations and a structure with a large number of dislocations is also demonstrated
Search for a low-mass pseudoscalar Higgs boson produced in association with a b-bbar pair in pp collisions at sqrt(s) = 8 TeV
No full textSee paper for full list of authors - Submitted to Phys. Lett. BInternational audienceA search is reported for a light pseudoscalar Higgs boson decaying to a pair of tau leptons, produced in association with a b-bbar pair, in the context of two-Higgs-doublet models. The results are based on pp collision data at a centre-of-mass energy of 8 TeV collected by the CMS experiment at the LHC and corresponding to an integrated luminosity of 19.7 inverse-femtobarns. Pseudoscalar boson masses between 25 and 80 GeV are probed. No evidence for a pseudoscalar boson is found and upper limits are set on the production cross section times branching fraction to tau pairs between 7 and 39 pb at the 95% confidence level. This search excludes a pseudoscalar Higgs boson with mass below 80 GeV, in Type II two-Higgs-doublet models with a negative coupling of standard model-like Higgs boson to down-type fermions