Institut de recherche mathématique avancée

Résumé : The exploration of the Low Surface Brightness (LSB) Universe currently motivates several surveys across the world, carried out with a number of instruments, and provides observational constrains for numerical simulations. It impacts multiple scientific fields, including the structure of the interstellar matter, galaxy archeology, galaxy evolution and cosmology, and has generated passionate debates, for instance regarding the very existence, nature and properties of the so called Ultra-Diffuse-Galaxies. Meanwhile the community prepares for the exploitation of next generation surveys, including Euclid and LSST. Detecting, identifying and characterising the faint, diffuse and extended optical light of the LSB structures on very wide areas on the sky raises a number of technical difficulties and challenges, that will be presented during the seminar. The first attempts to use artificial intelligence, and in particular deep learning techniques, to deal with these issues will be addressed. About the speaker: Pierre-Alain Duc is CNRS research director at the Observatoire Astronomique de Strasbourg and director of the observatory since 2017. He defended his PhD thesis in 1994 at CEA Saclay on the formation of dwarf galaxies in interacting systems before moving to ESO Garching and the university of Cambridge for postdoctoral studies. He joined the CNRS in 1999 at CEA Saclay before moving to Strasbourg to take charge of the observatory. Among his numerous research topics, he is particularly interested in the study of environmental effects on the formation and evolution of galaxies. Pierre-Alain is the PI of the MATLAS large program at CFHT and member of the Euclid and Rubin/LSST consortiums.

Résumé : Dans cet exposé je présenterai une nouvelle construction à « l’infini temporel » d’une variété lorentzienne asymptotiquement plate et donnerai des arguments en faveur de son application à l’analyse du comportement asymptotique de solutions de l’équation de Klein-Gordon sur une telle variété.

Résumé : The study of the maximum displacement of branching particle systems have seen some remarkable progress in the past decade. In this talk, I will consider a variant of the branching Brownian motion in dimension 2 for which the branching rate depends on the direction of the particles. Together with David Geldbach and Michel Pain, we show that this type of space inhomogeneities can yield some extra polynomial lag terms compared to the homogeneous case.

Résumé : Let $X$ be a smooth projective integral variety over a finitely generated field $k$ of characteristic $p>0$. We show that the finiteness of the exponent of the $p$-primary part of $Br(X_{k^s})^{G_k}$ is equivalent to the Tate conjecture for divisors, generalizing D'Addezio's theorem for abelian varieties to arbitrary smooth projective varieties. In combination with the Leray spectral sequence for rigid cohomology derived from the Berthelot conjecture recently proved by Ertl-Vezzani, we show that the cokernel of $Br_{nr}(K(X)) \rightarrow Br(X_{k^s})^{G_k}$ has finite exponent. This completes the $p$-primary part of the generalization of Artin-Grothendieck's theorem on relations between Brauer groups and Tate-Shafarevich groups to higher relative dimensions. This is joint with Zhenghui Li

Résumé : Lien pour la visio-conférence : https://bbb.unistra.fr/b/fre-cjl-bda-dum