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The cone topology on masures. With an appendix by Auguste Hébert (Université de Lyon). (English) Zbl 1433.51008

Summary: Masures are generalizations of Bruhat-Tits buildings and the main examples are associated with almost split Kac-Moody groups \(G\) over non-Archimedean local fields. In this case, \(G\) acts strongly transitively on its corresponding masure \(\Delta\) as well as on the building at infinity of \(\Delta \), which is the twin building associated with \(G\). The aim of this article is twofold: firstly, to introduce and study the cone topology on the twin building at infinity of a masure. It turns out that this topology has various favorable properties that are required in the literature as axioms for a topological twin building. Secondly, by making use of the cone topology, we study strongly transitive actions of a group \(G\) on a masure \(\Delta \). Under some hypotheses, with respect to the masure and the group action of \(G\), we prove that \(G\) acts strongly transitively on \(\Delta\) if and only if it acts strongly transitively on the twin building at infinity \(\partial \Delta \). Along the way a criterion for strong transitivity is given and the existence and good dynamical properties of strongly regular hyperbolic automorphisms of the masure are proven.

MSC:

51E24 Buildings and the geometry of diagrams
20E42 Groups with a \(BN\)-pair; buildings
20G44 Kac-Moody groups
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