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2y

Automorphisms of hyperbolic groups and growth - Horbez, Camille (Author of the conference) | CIRM H

Post-edited

Let $G$ be a torsion-free hyperbolic group, let $S$ be a finite generating set of $G$, and let $f$ be an automorphism of $G$. We want to understand the possible growth types for the word length of $f^n(g)$, where $g$ is an element of $G$. Growth was completely described by Thurston when $G$ is the fundamental group of a hyperbolic surface, and can be understood from Bestvina-Handel's work on train-tracks when $G$ is a free group. We address the general case of a torsion-free hyperbolic group $G$; we show that every element in $G$ has a well-defined exponential growth rate under iteration of $f$, and that only finitely many exponential growth rates arise as $g$ varies in $G$. In addition, we show the following dichotomy: every element of $G$ grows either exponentially fast or polynomially fast under iteration of $f$.
This is a joint work with Rémi Coulon, Arnaud Hilion and Gilbert Levitt.[-]
Let $G$ be a torsion-free hyperbolic group, let $S$ be a finite generating set of $G$, and let $f$ be an automorphism of $G$. We want to understand the possible growth types for the word length of $f^n(g)$, where $g$ is an element of $G$. Growth was completely described by Thurston when $G$ is the fundamental group of a hyperbolic surface, and can be understood from Bestvina-Handel's work on train-tracks when $G$ is a free group. We address the ...[+]

57M07 ; 20E06 ; 20F34 ; 20F65 ; 20E36 ; 20F67

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2y
Pants complexes of large surfaces were proved to be vigid by Margalit. We will consider convergence completions of curve and pants complexes and show that some weak four of rigidity holds for the latter. Some key tools come from the geometry of Deligne Mumford compactification of moduli spaces of curves with level structures.

57M10 ; 20F34 ; 14D23

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y

Spaces of cubulations - Fioravanti, Elia (Author of the conference) | CIRM H

Virtualconference

The theory of group actions on CAT(0) cube complexes has exerted a strong influence on geometric group theory and low-dimensional topology in the last two decades. Indeed, knowing that a group G acts properly and cocompactly on a CAT(0) cube complex reveals a lot of its algebraic structure. However, in general, "cubulations'' are non-canonical and the group G can act on cube complexes in many different ways. It is thus natural to try and formulate a good notion of "space of all cubulations of G'', which would prove useful in the study of Out(G) for quite general groups G. I will describe some results in this direction, based on joint works with J. Beyrer and M. Hagen.[-]
The theory of group actions on CAT(0) cube complexes has exerted a strong influence on geometric group theory and low-dimensional topology in the last two decades. Indeed, knowing that a group G acts properly and cocompactly on a CAT(0) cube complex reveals a lot of its algebraic structure. However, in general, "cubulations'' are non-canonical and the group G can act on cube complexes in many different ways. It is thus natural to try and ...[+]

20F65 ; 20F67 ; 20F34 ; 57-XX

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y

Spin mapping class groups and curve graphs - Hamenstädt, Ursula (Author of the conference) | CIRM H

Virtualconference

A spin structure on a closed surface $S$ of genus $g \geq 2$ is a covering of the unit tangent bundle of $S$ witch restricts to a standard covering of the fiber. Such a spin structure has a parity, even or add. The spin mapping class is the stabilizer of such a spin structure in the mapping class group of $S$. We use a subgraph of the curve graph to construct an explicit generating set of the spin mapping class group consisting of Dehn twists about a system of $2g-1$ simple closed curves.[-]
A spin structure on a closed surface $S$ of genus $g \geq 2$ is a covering of the unit tangent bundle of $S$ witch restricts to a standard covering of the fiber. Such a spin structure has a parity, even or add. The spin mapping class is the stabilizer of such a spin structure in the mapping class group of $S$. We use a subgraph of the curve graph to construct an explicit generating set of the spin mapping class group consisting of Dehn twists ...[+]

20F65 ; 20F34 ; 20F28

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