GT et PÉC de l'équipe Combinatoire et Interactions
La petite école et le séminaire de l'équipe Combinatoire et Interactions (CI) ont lieu les lundis. Les horaires sont de de 9h30 à 10h30 pour la PÉC et de 10h45 à 11h45 pour le GT. Ils ont lieu dans la salle 076 au rez-de-chaussée du LaBRI (bâtiment A30).
Lorsque l'exposé est filmé il est retransmis via zoom
https://u-bordeaux-fr.zoom.us/j/83326403471?pwd=VLapX1qCOgASs3V8OktWtKEr8dn041.1
Meeting ID: 833 2640 3471
Passcode: 1251442
Contactez le responsable (Vincent Delecroix) si vous voulez proposer un exposé ou recevoir les annonces de la PÉC ou du GT.
Pour l'historique des exposés précédents, voir le menu "GT CI" à droite de la page.
2024-2025
Lundi 19 mai: Sean Raymond (CNRS, Laboratoire d'astrophysique de Bordeaux)
Title: Formation of "super-Earths": breaking the (resonant) chains
Abstract:
The most abundant population of exoplanets found to date are the "super-Earths" and "sub-Neptunes", which have sizes between that of Earth and Neptune and orbital periods shorter than Mercury's around the Sun. I will present the current leading model for the formation of these systems, which involves the inward orbital migration of cohorts of protoplanets during the gaseous protoplanetary disk phase. Migration generically produces chains in which neighboring planets are in mean motion resonance, with orbital periods that form a ratio of small integers (e.g., 2:1, 3:2, 4:3). In the vast majority of cases, these resonant chains are disrupted. However, in rare cases the resonant chains survive -- for instance, the iconic Trappist-1 system contains 7 ~Earth-sized planets in a long resonant chain. Resonant chains naturally encode integer sequences and are therefore of interest from a mathematical point of view.
Lundi 26 mai: Alessandro Giachetto
Title: Resurgence and large genus asymptotics of intersection numbers
Abstract: In this talk, I will present a new approach to the computation of the large genus asymptotics of Witten–Kontsevich intersection numbers. Our technique is based on a resurgent analysis of the n-point function of such intersection numbers, which are computed via determinantal formulae, and relies heavily on the presence of an underlying first-order differential system. With this approach, we are able to extend the recent results of Aggarwal with the computation of subleading corrections, and to obtain completely new results on r-spin and Theta-class intersection numbers. Based on the joint work with B. Eynard, E. Garcia-Failde, P. Gregori, D. Lewański.
Lundi 2 juin: Jarkko Kari
pique-nique d'équipe en 76
Title: Low complexity colorings of the two-dimensional grid
Abstract: A two-dimensional configuration is a coloring of the infinite grid Z^2 using a finite number of colors. For a finite subset D of Z^2, the D-patterns of a configuration are the patterns of shape D that appear in the configuration. The number of distinct D-patterns of a configuration is a natural measure of its complexity. We consider low-complexity configurations where the number of distinct D-patterns is at most |D|, the size of the shape. We use algebraic tools to study periodicity of such configurations. We show, for an arbitrary shape D, that a low-complexity configuration must be periodic if it comes from the well-known Ledrappier subshift, or from a wide family of other similar algebraic subshifts. We also discuss connections to the well-known Nivat's conjecture: In the case D is a rectangle - or in fact any convex shape - we establish that a uniformly recurrent configuration that has low-complexity with respect to shape D must be periodic. This implies an algorithm to determine if a given collection of mn rectangular patterns of size mxn admit a configuration containing only these patterns. Without the complexity bound the question is the well-known undecidable domino problem.
Mercredi 4 juin 14h (dans l'amphi) : Soutenance HDR Sébastien Labbé
Lundi 9 juin: pentecôte
Lundi 16 juin: à saisir
Lundi 23 juin: Raquel Melgar
Lundi 30 juin: à saisir