The tree lattice existence theorems
[Les théorèmes d'existence de réseaux associés aux arbres]
Comptes Rendus. Mathématique, Tome 335 (2002) no. 3, pp. 223-228.

Soit X un arbre localement fini, et soit G=Aut(X). Alors G est un groupe localement compact. Par analogie avec les groupes de Lie, Bass et Lubotzky ont conjecturé que G contient des réseaux, c'est-à-dire des sous-groupes discrets dont le quotient porte une mesure invariante finie. Bass et Kulkarni ont montré que G contient des réseaux uniformes si et seulement si G est unimodulaire et GX est fini. Nous décrivons les conditions nécessaires et suffisantes pour que G contienne des réseaux, non seulement uniformes mais aussi non-uniformes, prouvant ainsi complètement les conjectures de Bass et Lubotzky.

Let X be a locally finite tree, and let G=Aut(X). Then G is a locally compact group. In analogy with Lie groups, Bass and Lubotzky conjectured that G contains lattices, that is, discrete subgroups whose quotient carries a finite invariant measure. Bass and Kulkarni showed that G contains uniform lattices if and only if G is unimodular and GX is finite. We describe the necessary and sufficient conditions for G to contain lattices, both uniform and non-uniform, answering the Bass–Lubotzky conjectures in full.

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DOI : 10.1016/S1631-073X(02)02474-3
Carbone, Lisa 1

1 Department of Mathematics, Rutgers, The State University of New Jersey, 110 Frelinghuysen Rd, Piscataway, NJ 08854-8019, USA
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Carbone, Lisa. The tree lattice existence theorems. Comptes Rendus. Mathématique, Tome 335 (2002) no. 3, pp. 223-228. doi : 10.1016/S1631-073X(02)02474-3. http://archive.numdam.org/articles/10.1016/S1631-073X(02)02474-3/

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[9] L. Carbone, G. Rosenberg, Lattices on non-uniform trees, Geom. Dedicate (2002), to appear

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