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Generative Models of 21cm EoR Lightcones with 3D Scattering Transforms
No full textInternational audienceThe 21cm signal from the Epoch of Reionization (EoR) is observed as a three-dimensional data set known as a lightcone, consisting of a redshift (frequency) axis and two spatial sky plane axes. When observed by radio interferometers, this EoR signal is strongly obscured by foregrounds that are several orders of magnitude stronger. Due to its inherently non-Gaussian nature, the EoR signal requires robust statistical tools to accurately separate it from these foreground contaminants, but current foreground separation techniques focus primarily on recovering the EoR power spectrum, often neglecting valuable non-Gaussian information. Recent developments in astrophysics, particularly in the context of the Galactic interstellar medium, have demonstrated the efficacy of scattering transforms - novel summary statistics for highly non-Gaussian processes - for component separation tasks. Motivated by these advances, we extend the scattering transform formalism from two-dimensional data sets to three-dimensional EoR lightcones. To this end, we introduce a 3D wavelet set from the tensor product of 2D isotropic wavelets in the sky plane domain and 1D wavelets in the redshift domain. As generative models form the basis of component separation, our focus here is on building and validating generative models that can be used for component separation in future projects. To achieve this, we construct maximum entropy generative models to synthesise EoR lightcones, and statistically validate the generative model by quantitatively comparing the synthesised EoR lightcones with the single target lightcone used to construct them, using independent statistics such as the power spectrum and Minkowski Functionals. The synthesised lightcones agree well with the target lightcone both statistically and visually, opening up the possibility of developing for component separation methods using 3D scattering transforms
The Schouten-Nijenhuis bracket, codifferential of products and generalized interior products of p-forms
No full textInternational audienceIdentities pertaining to the de Rham codifferential δ in differential geometry are scattered in the literature. This article gathers such formulas involving usual differential operators (Lie derivative, Schouten-Nijenhuis bracket, etc.), while adding some new ones using a natural extension of the interior product, to provide a compact handy summary
Particle acceleration signatures in the time-dependent one-zone synchrotron self-Compton model of blazar flares
No full textInternational audienceThe study of multiwavelength flux and spectral variations during rapid flares from blazars provides strong constraints on the physical parameters of the compact emission regions responsible for these still poorly understood events. Although a full description of the continuous and transient emission from blazars seems to require more sophisticated scenarios, particle acceleration and loss mechanisms can be approximately described within the simple leptonic one-zone framework, enabling a systematic study of their impact on the observable properties of multiwavelength flare light curves. Our goal is to identify characteristic signatures in these light curve profiles that permit one to discriminate between the main physical processes situated inside the relativistic jet and commonly invoked to explain blazar flares. The present study exclusively focuses on modeling rapid flares from BL Lac type objects, which can be described within the synchrotron self-Compton (SSC) emission scenario. Combinations of several commonly employed mechanisms to describe the gain and loss of energetic particles in onezone models during flaring events are studied in a systematic way: particle injection; diffusive shock and stochastic acceleration and reacceleration; particle escape; adiabatic losses; radiative losses through synchrotron and inverse-Compton radiation. The current study is limited to the case of "hard-sphere" scattering. A large variety of light curve shapes arises from the different scenarios under study. Characteristic signatures, in particular energy-dependent time delays and differences in the shapes of the rising part of the flare, should allow the distinction to be made between different injection and acceleration scenarios, given the availability of sufficiently high-quality multiwavelength data sets. This is illustrated with a simplified application to a flare event from the blazar Mrk 421
Transition 1point5, the platform for French academic research laboratories engaged in their environmental transition
No full textThis article presents an analysis, quantitative and qualitative, of the actions shared by French laboratories on the Transition 1point5 platform. This is an open-source web application, developed by the French research group Labos 1point5, that allows volunteer French laboratories to share the measures -the actions-they have taken to reduce their environmental footprint. We present the analysis of the 274 actions shared by 69 laboratories on the platform on 11 June 2025, addressing the following questions. What measures are research laboratories implementing to adopt sustainable practices? Is there a single transition path that applies to all laboratories? What role do awareness-raising initiatives play in this process? Can participatory workshops add value to the transition process? Have laboratories undergoing transition effectively reduced their GHG (greenhouse gases) emissions?The main result of this study is that, rather than a single transition pathway, the platform's laboratories employ various approaches depending on their specific characteristics. These approaches share common features, such as the use of awareness-raising activities, the creation of working groups dedicated to environmental issues, and increasingly participatory workshops to discuss and implement transition actions. Another key finding is that it is too early to measure the effectiveness of the implemented measures in terms laboratories' GHG (greenhouse gas) reductions, since most of the laboratories only implemented their actions in 2024 or early 2025.Nevertheless, the platform provides valuable insights into how research laboratories are engaging in the transition, revealing organizational processes and demonstrating that another way to do research is explored.Cet article présente une analyse quantitative et qualitative des actions partagées par les laboratoires français sur la plateforme Transition 1point5. Il s'agit d'une application web open source, développée par le GDR Labos 1point5, qui permet aux laboratoires français volontaires de partager les mesures - les actions- qu'ils ont prises pour réduire leur empreinte environnementale. Nous présentons l'analyse des 274 actions partagées par 69 laboratoires sur la plateforme au 11 juin 2025, en abordant les questions suivantes. Quelles mesures les laboratoires de recherche mettent-ils en œuvre pour adopter des pratiques durables ? Existe-t-il une trajectoire de transition unique qui s'applique à tous les laboratoires ? Quel rôle jouent les initiatives de sensibilisation dans ce processus ? Les ateliers participatifs peuvent-ils apporter une valeur ajoutée au processus de transition ? Les laboratoires en transition ont-ils effectivement réduit leurs émissions de GES (gaz à effet de serre) ?Le principal résultat de cette étude est que, plutôt qu'une trajectoire de transition unique, les laboratoires de la plateforme emploient diverses approches en fonction de leurs caractéristiques spécifiques. Ces approches partagent des caractéristiques communes, telles que le recours à des activités de sensibilisation, la création de groupes de travail dédiés aux questions environnementales et des ateliers participatifs pour discuter et mettre en œuvre des actions de transition.Une autre conclusion importante est qu'il est trop tôt pour mesurer l'efficacité des mesures mises en œuvre en termes de réduction des émissions de gaz à effet de serre (GES) des laboratoires, car la plupart d'entre eux n'ont mis en œuvre leurs actions qu'en 2024 ou au début de 2025.Néanmoins, la plateforme fournit des informations importantes sur la manière dont les laboratoires de recherche s'engagent dans la transition, en révélant les processus organisationnels et en démontrant qu'une autre façon de mener des recherches est explorée
Massless Representations in Conformal Space and Their de Sitter (dS) Restrictions. The Split-Octonionic Fabric of Inflationary Field Dynamics
No full textInternational audienceThe monograph develops a self-contained, mathematically rigorous framework for massless representations of the conformal group U(2,2) and their restriction to the de Sitter group Sp(2,2). It systematically constructs ladder (massless) representations, computes invariant bilinear forms and Casimir operators, and provides explicit constructions of vertex operators and two-point functions for low-helicity fields. The monograph employs a novel Clifford-split-octonion approach, embedding 8-component Majorana spinors within an alternative composition algebra, which allows for fully explicit algebraic, spinorial, and geometric constructions. The text bridges foundational representation theory, explicit computational methods, and physical applications in quantum field theory and cosmology. While targeted at researchers in mathematical physics, quantum cosmology, and quantum field theory, the exposition is pedagogically structured to guide advanced graduate students through subtle algebraic and representation-theoretic ideas, making complex constructions accessible without sacrificing rigor
Magnetic reversals in a geodynamo model with a stably–stratified layer
No full textInternational audienceWe study the process of magnetic reversals in the presence of a stably-stratified layer below the core-mantle boundary using direct numerical simulations of the incompressible magnetohydrodynamics equations under the Boussinesq approximation in a spherical shell. We show that the dipolar-multipolar transition shifts to larger Rayleigh numbers in the presence of a stably-stratified layer, and that the dipolar strength of the magnetic field at the core-mantle boundary increases due to the skin effect. By imposing an heterogeneous heat flux at the outer boundary, we break the equatorial symmetry of the flow, and show that different heat flux patterns can trigger different dynamo solutions, such as hemispheric dynamos and polarity reversals. Using kinematic dynamo simulations, we show that the stably-stratified layer leads to similar growth rates of the dipole and quadrupole components of the magnetic field, playing the role of a conducting boundary layer, favouring magnetic reversals, and a dynamics predicted by low-dimensional models
Search for dimuon resonance in the 35 to 75 GeV mass range using 140 fb of 13 TeV collisions with the ATLAS detector
No full textInternational audienceA model-independent search for low-mass resonances decaying into pairs of oppositely charged muons is presented. The analysis uses proton-proton collision data corresponding to an integrated luminosity of 140 fb, recorded by the ATLAS detector at the Large Hadron Collider between 2015 and 2018. The search targets hypothetical dimuon resonances in the invariant mass range from 35 GeV to 75 GeV. The modelling of this mass region is particularly challenging for conventional analytic background parameterisations. To address this, a Gaussian process regression technique is used to model the background. The dimuon mass spectrum is analysed for potential signals, and no statistically significant excess is observed. Upper limits at the 95% confidence level are set on the fiducial production cross-section of new resonances decaying promptly into muons, ranging from 20 fb to 110 fb, depending on the resonance mass. These results are further interpreted in the context of dark-photon and dark-matter-mediator models, leading to new constraints on their parameter spaces
GWTC-4.0: Constraints on the Cosmic Expansion Rate and Modified Gravitational-wave Propagation
No full textInternational audienceWe analyze data from 142 of the 218 gravitational-wave (GW) sources in the fourth LIGO-Virgo-KAGRA Collaboration (LVK) Gravitational-Wave Transient Catalog (GWTC-4.0) to estimate the Hubble constant jointly with the population properties of merging compact binaries. We measure the luminosity distance and redshifted masses of GW sources directly; in contrast, we infer GW source redshifts statistically through i) location of features in the compact object mass spectrum and merger rate evolution, and ii) identifying potential host galaxies in the GW localization volume. Probing the relationship between source luminosity distances and redshifts obtained in this way yields constraints on cosmological parameters. We also constrain parameterized deviations from general relativity which affect GW propagation, specifically those modifying the dependence of a GW signal on the source luminosity distance. Assuming our fiducial model for the source-frame mass distribution and using GW candidates detected up to the end of the fourth observing run (O4a), together with the GLADE+ all-sky galaxy catalog, we estimate km s Mpc. This value is reported as a median with 68.3% (90%) symmetric credible interval, and includes combination with the measurement from GW170817 and its electromagnetic counterpart. Using a parametrization of modified GW propagation in terms of the magnitude parameter , we estimate , where recovers the behavior of general relativity
Quelques modes d'ondes stationnaires : cordes, membrane rectangulaire et circulaire, cavité cylindrique, cavité sphérique, modes transverses électriques et magnétiques
No full textMasterNous présentons dans ce cours de niveau variable selon les parties traitées (L2 à M1) quelques modes d'ondes stationnaires pouvant survenir au sein de structures à 1 dimension (cordes, modes électromagnétiques TEM), 2 dimensions (membranes rectangulaires ou circulaires) ou 3 dimensions (cavités cylindriques ou sphériques, mode transverse électrique TE ou magnétique TM au sein d'une cavité). Les modes d'ondes stationnaires sont présents dans la vie courante (vibration des cordes), dans l'enveloppe des étoiles comme le Soleil ou encore dans les cavités laser et accélératrices. Leur étude met en jeu l'équation d'Helmoltz et des outils nombreux de fonctions spéciales (Bessel, Legendre, harmoniques sphériques) dont les propriétés sont détaillées en annexes, et s'applique aux vibrations de quantités scalaires (élongation, pression) ou vectorielles (champs électromagnétiques)
The MeerKLASS L-band On-the-Fly Continuum Survey: Data Release 1
No full textInternational audienceThe MeerKAT Large Area Synoptic Survey (MeerKLASS) collaboration has acquired multiple passes of L-band (856-1712 MHz) scanning observations over a 268 deg sky region. This scanning enables efficient, large-area sky surveys by continuously scanning the MeerKAT array back and forth at fixed elevation while recording data at 2 sec intervals, progressively covering the survey region as the Earth rotates. We employ a novel on-the-fly (OTF) interferometric imaging technique to construct continuum images and catalogs from 16 hours of scan data. These data products, constituting the first MeerKLASS L-band data release (DR1), consist of high-fidelity radio continuum images and a catalogue of 34,874 radio sources detected with a SNR9. The resulting Stokes I images achieve a median noise level of 33 Jy beam and a median angular resolution of approximately . Cross-comparisons with previous surveys confirm the consistency of our flux density scale within 5% and astrometric precision within . Additionally, flux densities measured across the seven sub-bands enable in-band spectral-index estimates for the detected sources, providing insights into their physical properties and the broader source population. We compute the differential source counts, finding good agreement with existing measurements and validating our end-to-end processing. This data release demonstrates the effectiveness of scanning surveys when combined with OTF interferometric imaging. Commensal intensity mapping and interferometric imaging offers a dramatic enhancement of survey science per invested hour of observations and could therefore be an appealing option for next generation facilities like SKA-Mid