Séminaire de l’équipe SD
Responsables : Timothée BENARD, Charles FOUGERON et Mingkun LIU
Mercredi 25 mars 2026
13:30 Seonhee Lim (Seoul National University) 
Résumé
Diophantine approximation on Kleinian circle packings
Salle B405, bâtiment B, LAGA, Institut Galilée, Université Paris 13Kleinian circle packings are circle packings that are the limit sets of discrete subgroups of PSL(2, C). In this talk, we explore the Diophantine approximation of points of a Kleinian circle packing by the tangency points of the circles. For geometrically finite, acylindrical Kleinian circle packings, we establish a structure analogous to Bowen-Series maps. By a proper acceleration, we construct a conformal graph-directed Markov system for such a packing. We show that the quality of approximation is determined by the geometric lengths of cuspidal words, and provide an asymptotic formula for the Hausdorff dimension of the set of epsilon-badly approximable points. Similar questions are open for sphere packings associated with discrete subgroups of SO(n,1). (This talk is based on joint work with Yongquan Zhang and Kangrae Park.)
15:00 Nihar Gargava (Université Paris Saclay) Résumé
Shapes of unit lattices or totally real orders form a dense set of lattices
Salle B405, bâtiment B, LAGA, Institut Galilée, Université Paris 13Given a totally real number field of degree n>2, one can look at the ring of integers and consider the group of units. It is known by a classical theorem of Dirichlet that the group of units is given by a Euclidean lattice in n-1 dimensions. This also holds true if one considers the group of units in an order inside the ring of integers. One can then try to plot these lattices in the appropriate moduli space of Euclidean lattices in n-1 dimensions and ask where the points lie. It was conjectured by David–Shapira that for n=3 these unit lattices generate a dense set of lattices. I will explain the problem for n=3 and sketch the proof. (Joint with Nguyen-Thi Dang and Jialun Li.)
Mercredi 8 avril 2026
13:30 Selim Ghazouani ()
Titre bientôt disponible
Salle B405, bâtiment B, LAGA, Institut Galilée, Université Paris 13
15:00 Florestan Martin-Baillon ()
Titre bientôt disponible
Salle B405, bâtiment B, LAGA, Institut Galilée, Université Paris 13
Mercredi 15 avril 2026
13:30 Jacques Audibert (Leipzig)
Titre bientôt disponible
Salle B405, bâtiment B, LAGA, Institut Galilée, Université Paris 13
15:00 Nicolas Tholozan (ENS Ulm)
Titre bientôt disponible
Salle B405, bâtiment B, LAGA, Institut Galilée, Université Paris 13
Mercredi 20 mai 2026
11:00 Corentin Correia ()
Titre bientôt disponible
Salle B405, bâtiment B, LAGA, Institut Galilée, Université Paris 13
13:30 François Le Maître ()
Titre bientôt disponible
Salle B405, bâtiment B, LAGA, Institut Galilée, Université Paris 13
