Stability issues in the quasineutral limit of the one-dimensional Vlasov-Poisson equation

This work is concerned with the quasineutral limit of the one-dimensional Vlasov-Poisson equation, for initial data close to stationary homogeneous profiles. Our objective is threefold: first, we provide a proof of the fact that the formal limit does not hold for homogeneous profiles that satisfy the Penrose instability criterion. Second, we prove on the other hand that the limit is true for homogeneous profiles that satisfy some monotonicity condition, together with a symmetry condition. We handle the case of well-prepared as well as ill- prepared data. Last, we study a stationary boundary-value problem for the formal limit, the so-called quasineutral Vlasov equation. We show the existence of numerous stationary states, with a lot of freedom in the construction (compared to that of BGK waves for Vlasov-Poisson): this illustrates the degeneracy of the limit equation.Comment: 50 page

Exactly marginal deformations from exceptional generalised geometry

We apply exceptional generalised geometry to the study of exactly marginal deformations of $\mathcal{N}=1$ SCFTs that are dual to generic AdS$_5$ flux backgrounds in type IIB or eleven-dimensional supergravity. In the gauge theory, marginal deformations are parametrised by the space of chiral primary operators of conformal dimension three, while exactly marginal deformations correspond to quotienting this space by the complexified global symmetry group. We show how the supergravity analysis gives a geometric interpretation of the gauge theory results. The marginal deformations arise from deformations of generalised structures that solve moment maps for the generalised diffeomorphism group and have the correct charge under the generalised Reeb vector, generating the R-symmetry. If this is the only symmetry of the background, all marginal deformations are exactly marginal. If the background possesses extra isometries, there are obstructions that come from fixed points of the moment maps. The exactly marginal deformations are then given by a further quotient by these extra isometries. Our analysis holds for any $\mathcal{N}=2$ AdS$_5$ flux background. Focussing on the particular case of type IIB Sasaki-Einstein backgrounds we recover the result that marginal deformations correspond to perturbing the solution by three-form flux at first order. In various explicit examples, we show that our expression for the three-form flux matches those in the literature and the obstruction conditions match the one-loop beta functions of the dual SCFT.Comment: 52 page

High-redshift galaxies and black holes in the eyes of JWST: a population synthesis model from infrared to X-rays

The first billion years of the Universe is a pivotal time: stars, black holes (BHs) and galaxies form and assemble, sowing the seeds of galaxies as we know them today. Detecting, identifying and understand- ing the first galaxies and BHs is one of the current observational and theoretical challenges in galaxy formation. In this paper we present a population synthesis model aimed at galaxies, BHs and Active Galactic Nuclei (AGNs) at high redshift. The model builds a population based on empirical relations. Galaxies are characterized by a spectral energy distribution determined by age and metallicity, and AGNs by a spectral energy distribution determined by BH mass and accretion rate. We validate the model against observational constraints, and then predict properties of galaxies and AGN in other wavelength and/or luminosity ranges, estimating the contamination of stellar populations (normal stars and high-mass X-ray binaries) for AGN searches from the infrared to X-rays, and vice-versa for galaxy searches. For high-redshift galaxies, with stellar ages < 1 Gyr, we find that disentangling stellar and AGN emission is challenging at restframe UV/optical wavelengths, while high-mass X-ray binaries become more important sources of confusion in X-rays. We propose a color-color selection in JWST bands to separate AGN vs star-dominated galaxies in photometric observations. We also esti- mate the AGN contribution, with respect to massive, hot, metal-poor stars, at driving high ionization lines, such as C IV and He II. Finally, we test the influence of the minimum BH mass and occupa- tion fraction of BHs in low mass galaxies on the restframe UV/near-IR and X-ray AGN luminosity function.Comment: Accepted for publication in the Astrophysical Journa

AdS_5 Solutions of Type IIB Supergravity and Generalized Complex Geometry

We use the formalism of generalized geometry to study the generic supersymmetric AdS_5 solutions of type IIB supergravity that are dual to N=1 superconformal field theories (SCFTs) in d=4. Such solutions have an associated six-dimensional generalized complex cone geometry that is an extension of Calabi-Yau cone geometry. We identify generalized vector fields dual to the dilatation and R-symmetry of the dual SCFT and show that they are generalized holomorphic on the cone. We carry out a generalized reduction of the cone to a transverse four-dimensional space and show that this is also a generalized complex geometry, which is an extension of Kahler-Einstein geometry. Remarkably, provided the five-form flux is non-vanishing, the cone is symplectic. The symplectic structure can be used to obtain Duistermaat-Heckman type integrals for the central charge of the dual SCFT and the conformal dimensions of operators dual to BPS wrapped D3-branes. We illustrate these results using the Pilch-Warner solution.Comment: 56 pages; v2: minor changes, version to be published in Commun. Math. Phy

INTERETS ET LIMITES DU REGISTRE PARCELLAIRE GRAPHIQUE (RPG) POUR L'ANALYSE DU PROCESSUS D'AGRANDISSEMENT DES EXPLOITATIONS AGRICOLES

International audienceEntre 1970 et 2010, les deux tiers des exploitations agricoles ont cessé leur activité, alors que, dans le même temps, la taille moyenne des structures a quadruplé. Ce processus d’agrandissement des exploitations agricoles s’inscrit pleinement dans la « modernisation » de l’agriculture française et européenne à l’œuvre depuis les années 1960. En Basse-Normandie, région fortement spécialisée dans l’élevage laitier et marquée par la prédominance des paysages de bocage, la transformation des structures agricoles bouleverse les modèles d’organisation spatiale des exploitations laitières et imprime sa marque dans les paysages. Cette communication s’appuie sur la présentation d’un outil de suivi à haute fréquence du processus d’agrandissement des exploitations agricoles construit à partir des données du registre parcellaire graphique (RPG) de 2007, 2009 et 2011 en Basse-Normandie. L’exhaustivité spatiale et la finesse de résolution de cette base de données nous permettent en effet d’envisager la mise en place d’un observatoire multi-échelles de l’évolution des structures spatiales des exploitations agricoles. Ainsi, à l’échelle régionale, l’agrégation des données du registre parcellaire graphique permet d’analyser les transformations des systèmes de production et des structures paysagères. A l’échelle du bassin de production agricole, cette méthodologie permet de mieux comprendre le jeu complexe des recompositions du maillage d’exploitations agricoles et d’en décrypter les logiques spatiales. Des indicateurs statistiques cartographiables à une échelle fine sont ainsi proposés. Enfin, à l’échelle locale, un suivi dans le temps de la transformation des structures agricoles est mis en place. Le but est ici de retracer l’évolution de l’organisation spatiale des exploitations sur quatre ans au moyen d’indicateurs de statistiques spatiales (distance des parcelles au siège, pulvérisation et morcellement parcellaire...

Le rôle de la distance dans l'organisation des pratiques et des paysages agricoles : l'exemple du fonctionnement des exploitations laitières dans l'arc atlantique

International audienceIn the areas with a dairy production and in a hedgerow landscape surrounding, the farms appear as the elementary units of the structuration of rural spaces and landscape. The study of the logics of organization of the farmers' practices thus appears as a pertinent grid to analyse the dynamics of the transformations of agricultural spaces and landscapes. For the dairy farms of the Western Atlantic Europe, the factors linked to the morphology of the fields play a dominating part (plots pulverization, acreage of the farm). From this angle, the analysis of the part played by the distance of the fields from the farm buildings itself as far as the organization of the farmers' practices is concerned, takes on a central place. How can we take this distance into account and measure it too?The methods coming from the development of the Geographical Information Systems bring along, in this field, interesting advances. Making a grid based on distance criteria to read farmers' practices highlights the diversity of land use organization of dairy farms in various agricultural and spatial contexts (Galicia, Normandy and England). This diversity then sends back to the dynamics of changes of agricultural systems relating to the land concentration (increase of the farms' size, land consolidation), relating to the production system (specialization, intensification) and relating to the farms functioning (mechanization, automation, development of cooperative societies).Dans les régions laitières et bocagères, les exploitations agricoles sont souvent considérées comme les unités élémentaires de structuration de l'espace et du paysage rural. L'étude des logiques d'organisation des pratiques des agriculteurs apparaît ainsi comme une grille d'analyse pertinente des dynamiques de transformation de ces espaces et de ces paysages. Dans les exploitations laitières de l'Ouest Atlantique, les facteurs liés à la morphologie parcellaire (pulvérisation spatiale des parcelles, surface de l'exploitation) jouent un rôle prépondérant. Dans cette perspective, l'analyse du rôle de l'éloignement des parcelles par rapport au siège d'exploitation dans l'organisation des pratiques des agriculteurs revêt une place centrale. Comment prendre alors en compte et mesurer cet éloignement ? Les méthodes issues du développement des systèmes d'information géographique apportent, dans ce domaine, d'intéressantes avancées. La construction d'une grille de lecture des pratiques des agriculteurs, suivant le critère de la distance, permet en effet de mieux comprendre la diversité des modes d'organisation spatiale des exploitations laitières, et ce, dans des contextes agricoles et territoriaux très variés (Galice, Normandie et Angleterre). Cette diversité renvoie enfin aux dynamiques de transformation foncières (agrandissement, remembrement), productives (spécialisation, intensification) et fonctionnelles (mécanisation, automatisation, développement des organisations sociétaires) des systèmes agricoles

Orientational wetting and topological transitions in confined solutions of semi-flexible polymers

Despite their considerable practical and biological applications, the link between molecular properties, assembly conditions and self-organized structure in confined polymer solutions remains elusive. Here, we explore the lyotropic nematic ordering of semi-flexible chains in spherical confinement for multiple contour lengths across a wide regime of concentrations. We uncover an original crossover from two distinct quadrupolar states, both characterized by regular tetrahedral patterns of surface topological defects, to either longitudinal, latitudinal or spontaneously-twisted bipolar structures with increasing densities. These transitions, along with the intermediary arrangements that they involve, are attributed to the combination of orientational wetting with subtle variations in their liquid-crystal (LC) elastic anisotropies. Our molecular simulations are corroborated by density functional calculations, and are quantified through the introduction of several order parameters as well as an unsupervised learning scheme for the localization of topological defects. Our results agree quantitatively with the predictions of continuum nematic elasticity theories, and evidence the extent to which the folding of macromolecules and the self-assembly of low-molecular-weight LCs may be guided by the same, universal principles.Comment: arXiv admin note: substantial text overlap with arXiv:2107.0259