Bootstrapping in convergence groups.
We prove that the boundary of a right-angled hyperbolic building is a universal Menger space. As a consequence, the 3-dimensional universal Menger space is the boundary of some Gromov-hyperbolic group.
We prove that the natural map from bounded to usual cohomology is injective if is an irreducible cocompact lattice in a higher rank Lie group. This result holds also for nontrivial unitary coefficients, and implies finiteness results for : the stable commutator length vanishes and any –action on the circle is almost trivial. We introduce the continuous bounded cohomology of a locally compact group and prove our statements by relating to the continuous bounded cohomology of the ambient group...
We give homological conditions on groups such that whenever the conditions hold for a group G, there is a bound on the orders of finite subgroups of G. This extends a result of P. H. Kropholler. We also suggest a weaker condition under which the same conclusion might hold.
On étudie les morphismes d’un groupe infini discret dans un groupe de Lie contenu dans le groupe des difféomorphismes de la droite réelle. À un tel morphisme , on associe deux ensembles de “bouts” de “dans la direction” . On calcule le nombre de bouts dans plusieurs situations. Dans le cas particulier où est de type fini et où est le groupe des translations, n’a qu’un bout dans la direction si, et seulement si, ils vérifient la propriété de Bieri-Neumann-Strebel.