Algèbre et géométrie

14.00 - 14.45 : Naomi Andrew (Laboratoire de Mathématiques d'Orsay)Title: Automorphisms behaving badlyAbstract: Baumslag–Solitar groups are HNN extensions of the infinite cyclic group, whose isomorphism type is controlled by two integers giving the two embeddings. They have provided many counterexamples over the years: for example, they include groups which are not Hopfian and groups which are Hopfian but not residually finite. Later, Collins and Levin showed that there are Baumslag–Solitar groups that do not have finitely generated automorphism group. Moving this construction to higher rank, one can study "Leary–Minasyan groups": these are […]

14.00 - 14.45 : Jean Lécureux (Université de Bordeaux)Title: A simple lattice in an affine building Abstract: Affine buildings appear naturally in the study of algebraic groups over local fields: the first example is the tree on which acts SL_2(Q_p). Lattices in these algebraic groups are, in higher rank, arithmetic, and in every case, residually finite (hence never simple). Nevertheless, the main result that I will present implies that there exists a simple group which acts properly discontinuously and cocompactly on an affine building. The construction of this group is due to Titz-Mite […]

14.00 - 14.45 : Xenia Flamm (MPI Leipzig - IHES)  Title: Positive representations and non-Archimedean ordered fields Summary: Positive representations were introduced by Olivier Guichard and Anna Wienhard in their foundational work on higher Teichmüller theory. In this talk, we propose a notion of positive representation from the fundamental group of a (possibly non-closed) hyperbolic surface into the k-points of a reductive algebraic group, where k is an ordered field. Our approach provides a common framework that simultaneously extends the classical theory for closed surfaces and real Lie groups. We focus on the non-Archimedean case, […]

14:00-14:45 Adrien Boyer (IMJ-PRG): Property RD and Boundary Representations for A2 Buildings 15:00-15:45 Julien Marché (ENS – PSL): Action of endomorphisms of free groups on their SL_2-character varieties 16:15-17:00 Greg Patchell (University of Oxford): Selfless Inclusions of C*-Algebras and Quantum Groups Abstracts: Greg Patchell: Selfless Inclusions of C*-Algebras and Quantum Groups Recently, strong asymptotic freeness, or selflessness, in C-algebras has emerged as a powerful technique to prove important regularity properties including simplicity, unique trace, stable rank 1, and strict comparison. In particular, in Fall 2024, Amrutam, Gao, Kunnwalkam Elayavalli, and […]

14.00 - 14.45   Elia Fioravanti (KIT - Karlsruhe) "Generators for automorphisms of special groups"15.00 - 15.45   Enrico Le Donne (University of Fribourg) "Asymptotic geometry of Riemannian nilpotent groups"16.15 - 17.00   Catherine Pfaff (Queen's University) "A "cubist" decomposition of the Handel-Mosher axis bundle" Abstracts: Elia Fioravanti: Generators for automorphisms of special groups  Given a family F of finitely generated groups, do all groups in F have “tame” automorphisms, or can there be “wild” examples? More concretely, is Out(G) finitely generated for all groups G in the family F? Rips and Sela showed in the 90s […]