Measurement of event-plane correlations in √s_NN=2.76 TeV lead-lead collisions with the ATLAS detector

A measurement of event-plane correlations involving two or three event planes of different order is presented as a function of centrality for 7 μb −1 Pb+Pb collision data at √s NN =2.76 TeV, recorded by the ATLAS experiment at the Large Hadron Collider. Fourteen correlators are measured using a standard event-plane method and a scalar-product method, and the latter method is found to give a systematically larger correlation signal. Several different trends in the centrality dependence of these correlators are observed. These trends are not reproduced by predictions based on the Glauber model, which includes only the correlations from the collision geometry in the initial state. Calculations that include the final-state collective dynamics are able to describe qualitatively, and in some cases also quantitatively, the centrality dependence of the measured correlators. These observations suggest that both the fluctuations in the initial geometry and the nonlinear mixing between different harmonics in the final state are important for creating these correlations in momentum space.

Flexibility Properties in Complex Analysis and Affine Algebraic Geometry

In the last decades affine algebraic varieties and Stein manifolds with big (infinite-dimensional) automorphism groups have been intensively studied. Several notions expressing that the automorphisms group is big have been proposed. All of them imply that the manifold in question is an Oka–Forstnerič manifold. This important notion has also recently merged from the intensive studies around the homotopy principle in Complex Analysis. This homotopy principle, which goes back to the 1930s, has had an enormous impact on the development of the area of Several Complex Variables and the number of its applications is constantly growing. In this overview chapter we present three classes of properties: (1) density property, (2) flexibility, and (3) Oka–Forstnerič. For each class we give the relevant definitions, its most significant features and explain the known implications between all these properties. Many difficult mathematical problems could be solved by applying the developed theory, we indicate some of the most spectacular ones.

Blackfolds, plane waves and minimal surfaces

Minimal surfaces in Euclidean space provide examples of possible non-compact horizon geometries and topologies in asymptotically flat space-time. On the other hand, the existence of limiting surfaces in the space-time provides a simple mechanism for making these configurations compact. Limiting surfaces appear naturally in a given space-time by making minimal surfaces rotate but they are also inherent to plane wave or de Sitter space-times in which case minimal surfaces can be static and compact. We use the blackfold approach in order to scan for possible black hole horizon geometries and topologies in asymptotically flat, plane wave and de Sitter space-times. In the process we uncover several new configurations, such as black helicoids and catenoids, some of which have an asymptotically flat counterpart. In particular, we find that the ultraspinning regime of singly-spinning Myers-Perry black holes, described in terms of the simplest minimal surface (the plane), can be obtained as a limit of a black helicoid, suggesting that these two families of black holes are connected. We also show that minimal surfaces embedded in spheres rather than Euclidean space can be used to construct static compact horizons in asymptotically de Sitter space-times.

"Montrer au linguiste ce qu'il fait". Une analyse épistémologique du structuralisme européen (Hjelmslev, Jakobson, Martinet, Benveniste) dans sa filiation saussurienne

Cette thèse consiste en une analyse épistémologique comparée et très détaillée de l’ensemble du corpus saussurien publié ainsi que d’une portion très significative des oeuvres de Hjelmslev, Jakobson, Martinet et Benveniste. Il s’agit de montrer qu’en dépit d’une filiation revendiquée le structuralisme européen n’est pas saussurien, et par là de faire apparaître, par contrecoup, la spécificité de la problématique saussurienne, ainsi que ses enjeux pour la linguistique et plus largement pour les sciences de l’humain. La problématique saussurienne avait permis, pour la première fois dans l’histoire de la linguistique, une appréhension théorique de la langue. La problématique structuraliste est en revanche entièrement empirique, de sorte que sa scientificité relève en réalité d’une idéologie scientifique, au sens de Georges Canguilhem. Le point nodal de cette radicale différence de problématique est l’absence de théorisation structuraliste du rapport son/sens, et corrélativement la mécompréhension du concept saussurien de système. Celui-ci devient alors structure, c’est-à-dire, comme nous tentons de le faire apparaître, appréhension structurale d’un objet dont la définition commune et évidente (celle de la langue comme instrument de communication) n’est pas remise en cause. A la problématique étiologique saussurienne, constitutive du concept de langue, répond ainsi une problématique analytique qui conduit quant à elle à la construction d’un objet (forme ou structure) en lieu et place d’un concept. Plus précisément, la problématique structuraliste est idiomologique. Elle manque ainsi la distinction entre langue et idiome dont nous tentons dès lors de démontrer la nécessité et le caractère constitutif de la théorisation de la langue et, au-delà, du langage, notamment dans le cadre d’une articulation entre linguistique et psychanalyse.

On the Closure of the Tame Automorphism Group of Affine Three-Space

We provide explicit families of tame automorphisms of the complex affine three-space which degenerate to wild automorphisms. This shows that the tame subgroup of the group of polynomial automorphisms of C3 is not closed, when the latter is seen as an infinite-dimensional algebraic group.