Géométrie et Théorie des Modèles

Zoé Chatzidakis, co-organiser and co-founder (together with François Loeser, in 2006) of the GTM seminar, passed away on the 22nd of January 2025 in Paris. Zoé had been for years the life and soul of the scientific life in model theory, in Paris and abroad; this was an immense loss for the mathematical community and for her many friends.

Fondateurs : Zoé Chatzidakis (vous trouverez ici un lien vers le prix de thèse décerné à sa mémoire) et François Loeser.

Organisateurs : Raf Cluckers, Georges Comte, Antoine Ducros, Tamara Servi.

Vous pourrez également trouver les informations relatives au GTM sur sa page dédiée du site des évènements co-organisés par l'IMJ-PRG.

Pour s'abonner à la liste de diffusion de nos messages, consultez https://listes-lm.math.univ-paris-diderot.fr/sympa/help/user-subscribe.html.

Les vidéos des exposés passés sont accessibles ici.

PROCHAINE SÉANCE

Vendredi 2 octobre 2026 (salle Pierre Grisvard, IHP, 3ème étage du bâtiment Borel).

11h00. François Loeser (SU). Nash structure of curves over a valued field and tame henselian rationality.

In joint work with Antoine Ducros we provide a new proof, model-theoretic and geometric in nature, of the tame henselian rationality theorem of Kuhlmann. The proof takes place within the framework of stable completions of algebraic varieties over a valued field. It relies on two main results of independent interest: a Nash structure theorem for the stable completion of an algebraic curve and a tame descent theorem for abstract open polydiscs.

14h15. Antonio Lerario (Trieste). Titre et résumé à venir.

16h00. Isaac Goldring (UC Irvine). On the undecidability of the QWEP for C*-algebras.

In his landmark 1993 paper, Kirchberg introduced a property of C*-algebras called the QWEP, which stands for “quotient of the weak expectation property”. As the name suggests, the property is defined by the fact that the algebra is a quotient of a C*-algebra with the weak expectation property, which was a property introduced by Lance years earlier in connection with the theory of tensor products of C*-algebras. While at first glance this seems to be a strange property, Kirchberg showed that whether or not every C*-algebra has the QWEP is equivalent to the famous Connes Embedding Problem (CEP) from von Neumann algebra theory. The CEP remained open for nearly 50 years until its recent refutation in 2020 via a result in quantum complexity theory (as well as the equivalence with Kirchberg’s QWEP conjecture). Several years ago, I showed that the QWEP is an axiomatizable property of C*-algebras. In this talk, I will present joint work with Aruseelan and Hart where we show that the QWEP does not have an effective axiomatization and, in fact, there can be no effectively axiomatizable satisfiable theory of C*-algebras all of whose models have the QWEP (modulo some nontrivially conditions). The proofs uses the connection with the quantum complexity results mentioned above as well as other techniques from C*-algebra theory. No prior knowledge of continuous logic, operator algebras, or quantum complexity will be assumed.

SÉANCES ULTÉRIEURES

Programme des séances passées : 2006-07, 2007-08, 2008-09, 2009-10, 2010-11, 2011-12, 2012-13, 2013-14, 2014-15, 2015-16, 2016-17, 2017-18, 2018-19, 2019-20, 2020-21, 2021-22, 2022-23, 2023-24, 2024-25, 2025-26.

Ce séminaire est subventionné par : l'IMJ-PRG, UPCité (APPR), le GDR EFI, et la bourse KU Leuven Grant IF C16/23/010.