HAL-Polytechnique
Not a member yet
51406 research outputs found
Sort by
Homotopy type of shellable -complexes and their homology groups
No full text25 pagesThe theory of shellable simplicial complexes brings together combinatorics, algebra, and topology in a remarkable way. Initially introduced by Alder for -simplicial complexes, recent work of Ghorpade, Pratihar, and Randrianarisoa extends the study of shellability to -matroid complexes and determines singular homology groups for a subclass of these -simplicial complexes. In this paper, we determine the homotopy type of shellable -simplicial complexes. Moreover, we establish the shellability of order complexes from lexicographically shellable -simplicial complexes, that include the -matroid complexes. This results in a comprehensive determination of the homology groups for any lexicographically shellable -complexes
Derivation of a 4-moment model for electron transport in Hall thrusters from a gyrokinetic model
No full textWe model the motion of a population of electrons in a strong electromagnetic field undergoing elastic electron/electron collisions. This regime is derived from a dimensional analysis of the electron confinement in Hall-effect thrusters. The electrons exhibit a very high cyclotron frequency and a E × B-drift, modelled by stiff PDEs at the mesoscopic scale. We obtain a gyrokinetic model in which the fastest oscillations of the system are filtered out by averaging the rotation of the electrons around the magnetic field lines. The model is derived in the strong electromagnetic field limit. Based on this gyrokinetic model, we then develop a 10-moment model. The averaging operation performed at the kinetic scale leads to symmetry properties that allow to reduce the 10-moment model to a 4-moment model.</div
The exact Wheeler-DeWitt equation for the scale-factor minisuperspace model
No full textInternational audienceWe consider the classical minisuperspace model describing a closed, homogeneous and isotropic Universe, with a positive cosmological constant. Upon canonical quantization, the infinite number of possible operator orderings in the quantum Hamiltonian leads to distinct Wheeler-DeWitt equations for the wavefunction of the Universe. Similarly, ambiguity arises in the path-integral formulation of , due to the infinite choices of path-integral measures for the single degree of freedom of the model. For each choice of path-integral measure, we determine the correct operator ordering of the quantum Hamiltonian and derive the exact form of the Wheeler-DeWitt equation, including all corrections in . Additionally, we impose Hermiticity of the Hamiltonian to deduce the Hilbert-space measure , which appears in the definition of the Hermitian inner product. Remarkably, all quantum predictions can be expressed through the combination , which satisfies a universal Wheeler-DeWitt equation, independent of the initial path-integral prescription. This result demonstrates that all seemingly distinct quantum theories arising from different quantization schemes of the same classical model are fundamentally equivalent
Small-scale interface dynamic modelling based on the geometric method of moments for a two-scale two-phase flow model with a disperse small scale
No full textInternational audienceIn this contribution, we develop a versatile formalism to derive unified two-phase models describing both the separated and disperse regimes as introduced by Loison et al. (2024). It relies on the stationary action principle and interface geometric variables.This contribution provides a novel method to derive small-scale models for the dynamics of the interface geometry.They are introduced here on a simplified case where all the scales and phases have the same velocity and that does not take into account large-scale capillary forces.The derivation tools yield a proper mathematical framework through hyperbolicity and signed entropy evolution.The formalism encompasses a hierarchy of small-scale reduced-order models based on a statistical description at a mesoscopic kinetic level and is naturally able to include the description of a disperse phase with polydispersity in size. This hierarchy includes both a cloud of spherical droplets and non-spherical droplets experiencing a dynamical behaviour through incompressible oscillations. The associated small-scale variables are moments of a number density function resulting from the geometric method of moments (GeoMOM).This method selects moments as small-scale geometric variables compatible with the structure and dynamics of the interface; they are defined independently of the flow topology and, therefore, this model allows the coupling of the two-scale flow with an inter-scale transfer.It is shown in particular that the resulting dynamics provides partial closures for the interface area density equation obtained from the averaging approach
Steering Laser-Produced THz Radiation in Air with Superluminal Ionization Fronts
No full textInternational audienceWe demonstrate that pulsed THz radiation produced in air by a focused ultrashort laser pulse can be steered to large angles or even in the backward direction with respect to the laser propagation axis. The emission angle is adjusted by the flying focus technique, which determines the speed and direction of the ionization front created by the single-color laser pulse. This easily adjustable THz source, being well separated from the intense laser, opens exciting applications for remote THz spectroscopy
Model-order reduction framework for non-linear dynamics problems involving multiple non-parameterised loading configurations for damage assessment
No full textInternational audienc
Higher derivative couplings with multi-tensor multiplets in 6D supergravity, action and anomalies
No full textInternational audienceWe revisit six-dimensional (1,0) supergravity coupled to nT tensor multiplets and Yang-Mills fields for nT>1 for which no covariant action exists. We construct the action in the Henneaux-Teitelboim approach and in the presence of a gauge anomaly. We moreover obtain the supersymmetric Green-Schwarz counterterm for the gravitational anomaly for arbitrary matter content
Search for meson decays to and final states
No full textInternational audienceA search for meson decays to the and final states is reported using a sample of proton-proton collisions collected by the LHCb experiment at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 6 fb. The decay is observed for the first time when requiring that the two electrons are consistent with coming from the decay of a or meson. The corresponding branching fractions are measured relative to the decay, where the two electrons are consistent with coming from the decay of a or meson. No evidence is found for the decay and world-best limits are set on its branching fraction. The results are compared to, and found to be consistent with, the branching fractions of the and decays recently measured by LHCb and confirm lepton universality at the current precision
Magnetic Anti-de Sitter Wormholes as seeds for Higgs Inflation
No full textInternational audienceWe show how certain types of magnetic asymptotically Anti-de Sitter Euclidean wormholes can catalyze the onset of inflation. These wormholes can be embedded as saddle point solutions of General Relativity coupled to the Standard Model, the inflaton being identified with the Higgs particle. Our scenario is based on the assumption that the quantum effective potential for the Higgs turns negative at a certain high energy window, in line with current measured values for the Higgs and Top quark masses. Within our proposal, we can estimate various parameters and physical quantities of interest, in consistency with current observational bounds
First evidence for direct CP violation in beauty to charmonium decays
No full textInternational audienceThe asymmetry and branching fraction of the CKM-suppressed decay are precisely measured relative to the favoured decay , using a sample of proton-proton collision data corresponding to an integrated luminosity of recorded at center-of-mass energy of during 2016--2018. The results of the asymmetry difference and branching fraction ratio are \begin{align*} \Delta\mathcal{A}^{C\!P} &\equiv \mathcal{A}^{C\!P}(B^+ \to J\mskip -3mu/\mskip -2mu\psi\,\pi^+) - \mathcal{A}^{C\!P}(B^+ \to J\mskip -3mu/\mskip -2mu\psi\,K^+) = (1.29 \pm 0.49 \pm 0.08) \times 10^{-2}, \end{align*}\begin{equation*} \mathcal{R}_{\pi/K} \equiv \frac{\mathcal{B}(B^+ \!\to J\mskip -3mu/\mskip -2mu\psi\,\pi^+)}{\mathcal{B}(B^+ \!\to J\mskip -3mu/\mskip -2mu\psi\,K^+)} = (3.852 \pm 0.022 \pm 0.018) \times 10^{-2}. \end{equation*} where the first uncertainties are statistical and the second systematic. A combination with previous LHCb results based on data collected at and in 2011 and 2012 yields and . The combined value deviates from zero by 3.2 standard deviations, providing the first evidence for direct violation in the amplitudes of beauty decays to charmonium final states