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In these lectures, we will report on some properties of the space of actions of a left-orderable group on the real line. We will notably describe the almost-periodic actions, the harmonic actions and their spaces.

20F60 ; 22F50 ; 37B05 ; 37E10 ; 57R30

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For a class of fundamental groups of closed oriented hyperbolic 3-manifolds acting on their Gromov boundary, we compute the K-theory of the associated crossed products in terms of the first homology group of the manifold. Using classification results of purely infinite C*-algebras, we conclude that there exist infinitely many pairwise nonisomorphic torsion-free hyperbolic groups acting on their boundary, for which all crossed products are isomorphic. As in all these cases the boundary is homeomorphic to the 2-sphere, we find infinitely many pairwise non-conjugate Cartan subalgebras with spectrum $S^2$ in such crossed products. This is joint work with Johannes Ebert and Julian Kranz.[-]

For a class of fundamental groups of closed oriented hyperbolic 3-manifolds acting on their Gromov boundary, we compute the K-theory of the associated crossed products in terms of the first homology group of the manifold. Using classification results of purely infinite C*-algebras, we conclude that there exist infinitely many pairwise nonisomorphic torsion-free hyperbolic groups acting on their boundary, for which all crossed products are ...[+]

46L35 ; 37B05

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Irreducible lattices in semi-simple Lie groups of higher rank are not left-orderable I'll report on the problem of the left orderability of lattices in semi-simple Lie groups, and give some insight of our joint proof with Bertrand Deroin that in rank at least two, an irreducible lattice is not left-orderable. The proof will make use of the tools developed in the minicourse of Bertrand.

20F60 ; 37B05 ; 22F50 ; 37E10 ; 57R30

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A (pseudo)-Anosov flow on a 3-manifold can be understood through its orbit space, a bifoliated plane with a natural action of the fundamental group of the manifold. In this minicourse, we will describe techniques to study the dynamics of these orbit space actions as a means to understand the topological theory and the classification of (pseudo)Anosov flows in dimension 3. This leads to a more general theory of 'Anosov-like' actions on bifoliated planes, which form a rich class of discrete dynamical systems including but not limited to the orbit space actions from flows.[-]

A (pseudo)-Anosov flow on a 3-manifold can be understood through its orbit space, a bifoliated plane with a natural action of the fundamental group of the manifold. In this minicourse, we will describe techniques to study the dynamics of these orbit space actions as a means to understand the topological theory and the classification of (pseudo)Anosov flows in dimension 3. This leads to a more general theory of 'Anosov-like' actions on bifoliated ...[+]

37D40 ; 57S25 ; 37B05 ; 37C10 ; 37C27 ; 37D20

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I will present results of three studies, performed in collaboration with M.Benli, L.Bowen, A.Dudko, R.Kravchenko and T.Nagnibeda, concerning the invariant and characteristic random subgroups in some groups of geometric origin, including hyperbolic groups, mapping class groups, groups of intermediate growth and branch groups. The role of totally non free actions will be emphasized. This will be used to explain why branch groups have infinitely many factor representations of type $II_1$.[-]

I will present results of three studies, performed in collaboration with M.Benli, L.Bowen, A.Dudko, R.Kravchenko and T.Nagnibeda, concerning the invariant and characteristic random subgroups in some groups of geometric origin, including hyperbolic groups, mapping class groups, groups of intermediate growth and branch groups. The role of totally non free actions will be emphasized. This will be used to explain why branch groups have infinitely ...[+]

20E08 ; 20F65 ; 37B05

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Sixty years ago Paul Halmos concluded his Lectures on Ergodic Theory with a chapter Unsolved Problems which contained a list of ten problems. I will discuss some of these and some of the work that has been done on them. He considered actions of $\mathbb{Z}$ but I will also widen the scope to actions of general countable groups.

37Axx ; 37B05

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We will show how minimal dynamical systems and etale groupoids can be used to construct finitely generated simple groups with prescribed properties. For example, one can show that there are uncountably many different growth types (in particular quasi-isometry classes) among finitely generated simple groups, or embed the Grigorchuk group into a simple torsion group of intermediate growth. Other properties like torsion and amenability will be also discussed.[-]

We will show how minimal dynamical systems and etale groupoids can be used to construct finitely generated simple groups with prescribed properties. For example, one can show that there are uncountably many different growth types (in particular quasi-isometry classes) among finitely generated simple groups, or embed the Grigorchuk group into a simple torsion group of intermediate growth. Other properties like torsion and amenability will be also ...[+]

22A22 ; 37B05 ; 20E32 ; 20L05

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A subgroup of a group is confined if the closure of its conjugacy class in the Chabauty space does not contain the trivial subgroup. Such subgroups arise naturally as stabilisers for non-free actions on compact spaces. I will explain a result establishing a relation between the confined subgroup of a group with its highly transitive actions. We will see how this result allows to understand the highly transitive actions of a class of groups of dynamical origin. This is joint work with Adrien Le Boudec.[-]

A subgroup of a group is confined if the closure of its conjugacy class in the Chabauty space does not contain the trivial subgroup. Such subgroups arise naturally as stabilisers for non-free actions on compact spaces. I will explain a result establishing a relation between the confined subgroup of a group with its highly transitive actions. We will see how this result allows to understand the highly transitive actions of a class of groups of ...[+]

20B22 ; 37B05 ; 22F05

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We say a pointed dynamical system is asymptotically nilpotent if every point tends to zero. We study group actions whose endomorphism actions are nilrigid, meaning that for all asymptotically nilpotent endomorphisms the convergence to zero is uniform. We show that this happens for a large class of expansive group actions on a large class of groups. The main examples are cellular automata on subshifts of finite type.

37B05 ; 37B15 ; 54H15

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A (pseudo)-Anosov flow on a 3-manifold can be understood through its orbit space, a bifoliated plane with a natural action of the fundamental group of the manifold. In this minicourse, we will describe techniques to study the dynamics of these orbit space actions as a means to understand the topological theory and the classification of (pseudo)Anosov flows in dimension 3. This leads to a more general theory of 'Anosov-like' actions on bifoliated planes, which form a rich class of discrete dynamical systems including but not limited to the orbit space actions from flows.[-]

A (pseudo)-Anosov flow on a 3-manifold can be understood through its orbit space, a bifoliated plane with a natural action of the fundamental group of the manifold. In this minicourse, we will describe techniques to study the dynamics of these orbit space actions as a means to understand the topological theory and the classification of (pseudo)Anosov flows in dimension 3. This leads to a more general theory of 'Anosov-like' actions on bifoliated ...[+]

37D40 ; 57S25 ; 37B05 ; 37C10 ; 37C27 ; 37D20

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Documents 37B05 13 résultats

Space of actions of groups on the real line - Deroin, Bertrand (Auteur de la Conférence) | CIRM H Nouveau

C*-algebras associated with boundary actions of certain torsion-free hyperbolic groups - Geffen, Shirly (Auteur de la Conférence) | CIRM H Nouveau

Irreducible lattices in semi-simple Lie groups of higher rank are not left-orderable - Hurtado Salazar, Sebastian (Auteur de la Conférence) | CIRM H Nouveau

Anosov flows in 3 dimensions and Anosov-like actions - Part 1 - Mann, Kathryn (Auteur de la Conférence) ; Barthelmé, Thomas (Auteur de la Conférence) | CIRM H Nouveau

Random subgroups, totally non free actions and factor representations - Grigorchuk, Rostislav (Auteur de la Conférence) | CIRM H Nouveau

The unsolved problems of Halmos - Weiss, Benjamin (Auteur de la Conférence) | CIRM H Nouveau

Constructing simple groups using dynamical systems - Nekrashevych, Volodymyr (Auteur de la Conférence) | CIRM H Nouveau

Confined subgroups and high transitivity - Matte Bon, Nicolás (Auteur de la Conférence) | CIRM H Nouveau

Nilpotent endomorphisms of expansive group actions - Salo, Ville (Auteur de la Conférence) | CIRM H Nouveau

Anosov flows in 3 dimensions and Anosov-like actions - Part 2 - Mann, Kathryn (Auteur de la Conférence) ; Barthelmé, Thomas (Auteur de la Conférence) | CIRM H Nouveau