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CHABAUTY LIMITS OF SIMPLE GROUPS ACTING ON TREES

  • Pierre-Emmanuel Caprace (a1) and Nicolas Radu (a1)
Abstract

Let $T$ be a locally finite tree without vertices of degree  $1$ . We show that among the closed subgroups of $\text{Aut}(T)$ acting with a bounded number of orbits, the Chabauty-closure of the set of topologically simple groups is the set of groups without proper open subgroup of finite index. Moreover, if all vertices of $T$ have degree ${\geqslant}3$ , then the set of isomorphism classes of topologically simple closed subgroups of $\text{Aut}(T)$ acting doubly transitively on $\unicode[STIX]{x2202}T$ carries a natural compact Hausdorff topology inherited from Chabauty. Some of our considerations are valid in the context of automorphism groups of locally finite connected graphs. Applications to Weyl-transitive automorphism groups of buildings are also presented.

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F.R.S.-FNRS Senior Research Associate, supported in part by the ERC (grant no. 278469).

F.R.S.-FNRS Research Fellow.

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Journal of the Institute of Mathematics of Jussieu
  • ISSN: 1474-7480
  • EISSN: 1475-3030
  • URL: /core/journals/journal-of-the-institute-of-mathematics-of-jussieu
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