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Topological Properties of Photonic Bands with Synthetic Momentum
No full textInternational audienceWe investigate topological aspects of photonic crystal bands in a hybrid momentum space consisting of a genuine momentum and a synthetic one. The system is realised by a one-dimensional system of bilayer photonic grating, with the translational displacement between the two layers naturally taking the role of the synthetic momentum. Remarkably, the unconventional behaviour of the synthetic momentum allows for the existence of non-trivial topological phases of the system associated with a non-zero total Berry flux without breaking the time-reversal symmetry. Moreover, the resulting band structure in the hybrid momentum space realises the interesting dynamics of merging and splitting of twin Dirac points, as well as gap opening as the system parameters vary. Introducing a simple topological argument, we explain all the changes of the total Berry flux associated with the topological phase transitions. As a signature of different topological phases, edge states at their interface are calculated and analysed in detail. The optomechanical nature of the system also allows for the investigation of the adiabatic evolution of the edge states. Our results pave the way to the paradigm of rich topological phenomena of photonic systems with hybrid momentum space
"Creoles in the Diaspora or Diasporic Creoles: Rethinking language emergence, patterns of (de-)creolization and normativity".
No full textLe laboureur et ses outils dans le glossaire gréco-copte de Dioscore d’Aphrodité (VIe siècle apr. J.-C.) : une source retrouvée, Hésiode, Les travaux et les jours, 427-439 et 467-469
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Level order of quark systems: The puzzle of the Roper resonance, and related questions
No full textInternational audienceThe problem of ordering of radial vs. orbital excitations is reviewed. It is shown that the current quark models cannot explain the location of the Roper resonance which is slightly lower than the lowest negative-parity excitations. We also study some related spectral problems, such as the dependence of the energies on the quark masses, and the possibility of bound states in simple chromelectric models
Measurements of the inclusive W and Z boson production cross sections and their ratios in proton-proton collisions at = 13.6 TeV
No full textInternational audienceMeasurements are presented of the W and Z boson production cross sections in proton-proton collisions at a center-of-mass energy of 13.6 TeV. Data collected in 2022 and corresponding to an integrated luminosity of 5.01 fb with one or two identified muons in the final state are analyzed. The results for the products of total inclusive cross sections and branching fractions for muonic decays of W and Z bosons are 11.93 0.08 (syst) 0.17 (lumi) (acc) nb for W boson production, 8.86 0.06 (syst) 0.12 (lumi) (acc) nb for W boson production, and 2.021 0.009 (syst) 0.028 (lumi) (acc) nb for the Z boson production in the dimuon mass range of 60-120 GeV, all with negligible statistical uncertainties. Furthermore, the corresponding fiducial cross sections, as well as cross section ratios for both fiducial and total phase space, are provided. The ratios include charge-separated results for W boson production (W and W) and the sum of the two contributions (W), each relative to the measured Z boson production cross section. Additionally, the ratio of the measured cross sections for W and W boson production is reported. All measurements are in agreement with theoretical predictions, calculated at next-to-next-to-leading order accuracy in quantum chromodynamics
Spatially-Controlled Planar Guided Crystallization of Low-Loss Phase Change Materials for Programmable Photonics
No full textInternational audiencePhotonic integrated devices are progressively evolving beyond passive components into fully programmable systems, notably driven by the progress in chalcogenide phase-change materials (PCMs) for non-volatile reconfigurable nanophotonics. However, the stochastic nature of their crystal grain formation results in strong spatial and temporal crystalline inhomogeneities. Here, we propose the concept of spatially-controlled planar Czochralski growth, a novel method for programming the quasi-monocrystalline growth of low-loss Sb2S3 PCM, leveraging the seeded directional and progressive crystallization within confined channels. This guided crystallization method is experimentally shown to circumvent the current limitations of conventional PCM-based nanophotonic devices, including a multilevel non-volatile optical phase-shifter exploiting a silicon nitride-based Mach-Zehnder interferometer, and a programmable metasurface with spectrally reconfigurable bound state in the continuum. Precisely controlling the growth of PCMs to ensure uniform crystalline properties across large areas is the cornerstone for the industrial development of non-volatile reconfigurable photonic integrated circuits
The Velocity Field Olympics: Assessing velocity field reconstructions with direct distance tracers
No full textInternational audienceThe peculiar velocity field of the local Universe provides direct insights into its matter distribution and the underlying theory of gravity, and is essential in cosmological analyses for modelling deviations from the Hubble flow. Numerous methods have been developed to reconstruct the density and velocity fields at , typically constrained by redshift-space galaxy positions or by direct distance tracers such as the Tully-Fisher relation, the fundamental plane, or Type Ia supernovae. We introduce a validation framework to evaluate the accuracy of these reconstructions against catalogues of direct distance tracers. Our framework assesses the goodness-of-fit of each reconstruction using Bayesian evidence, residual redshift discrepancies, velocity scaling, and the need for external bulk flows. Applying this framework to a suite of reconstructions -- including those derived from the Bayesian Origin Reconstruction from Galaxies (BORG) algorithm and from linear theory -- we find that the non-linear BORG reconstruction consistently outperforms others. We highlight the utility of such a comparative approach for supernova or gravitational wave cosmological studies, where selecting an optimal peculiar velocity model is essential. Additionally, we present calibrated bulk flow curves predicted by the reconstructions and perform a density-velocity cross-correlation using a linear theory reconstruction to constrain the growth factor, yielding . This result is in significant tension with Planck but agrees with other peculiar velocity studies
Development of an experimental method for the characterization of kinetic constants of hydrogenotrophic methanogenesis in mixed cultures: Overcoming mass-transfer limitations
No full textInternational audienceHydrogenotrophic methanogenesis is a key reaction in biological methanation processes. This reaction is known to be driven by both dynamics: the biological reaction itself, and the gas-to liquid mass transfer. Consequently, identifying biokinetic parameters of hydrogenotrophic methanogenesis is challenged by gas-liquid mass transfer limitations. To overcome this issue, an experimental setup was designed to operate at high pressure. Working at a high H2 partial pressure and at low biomass concentration enabled biologically driven dynamics to be observed, followed by mass transfer limitation. The transition towards the mass transfer regime was characterized by analyzing pressure dynamics. A numerical model was used to confirm this transition and to identify the biological kinetic parameters. The maximal growth rate in thermophilic mixed culture was between 0.18 and 0.22 h - 1
Convergence analysis of semi-smooth Newton method for mixed FEM approximations of dynamic two-body contact and crack problems
No full textInternational audienceA class of elastodynamic problems describing contact between two deformable bodies as well as non-penetrating cracks in a single body is considered in the framework of FEM approximation. For time discretization, the Hilber-Hughes-Taylor (HHT-alpha) method extending Newmark schemes is incorporated. Using mixed variational formulation of the fully discrete contact problem, a semi-smooth Newton method of solution is provided with the locally super-linear convergence. An equivalent primal-dual active set algorithm validates monotone properties of global convergence for the Newton iterates provided by M-matrix property. Numerical solution of the Signorini contact with rigid obstacle is presented for isotropic body in 2D using benchmark and moving load experiment
