Commability of groups quasi-isometric to trees
Annales de l'Institut Fourier, Volume 68 (2018) no. 4, p. 1365-1398
Commability is the finest equivalence relation between locally compact groups such that G and H are equivalent whenever there is a continuous proper homomorphism GH with cocompact image. Answering a question of Cornulier, we show that all non-elementary locally compact groups acting geometrically on locally finite simplicial trees are commable, thereby strengthening previous forms of quasi-isometric rigidity for trees. We further show that 6 homomorphisms always suffice, and provide the first example of a pair of locally compact groups which are commable but without commation consisting of less than 6 homomorphisms. Our strong quasi-isometric rigidity also applies to products of symmetric spaces and Euclidean buildings, possibly with some factors being trees.
La commabilité est la relation d’équivalence entre groupes localement compacts la plus fine telle que G et H sont équivalents dès qu’il existe un homomorphisme GH continu, propre et d’image cocompacte. Répondant à une question de Cornulier, nous montrons que tous les groupes localement compacts non-élémentaires agissant sur des arbres simpliciaux localement finis sont commables, renforçant les formes précédentes de rigidité quasi-isométrique pour les arbres. De plus, nous montrons que 6 homomorphismes suffisent toujours, et donnons le premier exemple d’une paire de groupes localement compacts qui sont commables mais n’ayant pas de commation constituée de moins de 6 homomorphismes. Notre rigidité quasi-isométrique forte s’applique également à des produits d’espace symétriques et d’immeubles euclidiens, dont certains facteurs sont éventuellement des arbres.
Received : 2013-11-28
Accepted : 2014-09-30
Published online : 2018-11-23
Classification:  22D05,  20F65,  20E08,  20E42
Keywords: Commability, groups acting on trees, quasi-isometric rigidity
     author = {Carette, Mathieu},
     title = {Commability of groups quasi-isometric to trees},
     journal = {Annales de l'Institut Fourier},
     publisher = {Association des Annales de l'institut Fourier},
     volume = {68},
     number = {4},
     year = {2018},
     pages = {1365-1398},
     doi = {10.5802/aif.3190},
     language = {en},
     url = {}
Commability of groups quasi-isometric to trees. Annales de l'Institut Fourier, Volume 68 (2018) no. 4, pp. 1365-1398. doi : 10.5802/aif.3190.

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