Séminaire : Stephan Tornier (The University of Newcastle, Australia)

Monday 18 Nov 2019, 14:00 → 16:00 Europe/Brussels

B203-05 (MdeHemptinne)

Titre: On the k-closures of locally transitive groups acting on trees

Résumé: We develop a generalisation of Burger-Mozes universal groups, acting on the d-regular tree T_d, by prescribing the local action on vertex neighbourhoods of a given radius k. In the locally transitive case, these groups are precisely the Banks-Elder-Willis k- closures of subgroups of Aut(T_d) which contain an edge inversion of order 2. As an application, we show that the simple groups associated to certain groups with pairwise distinct k-closures are pairwise non-isomorphic as topological groups.