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Spring Semester 2019

Date / Time Speaker Title Location
27 February 2019
15:45-16:45 		Ori Parzanchevski
Hebrew University
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Geometry Seminar

Title Random walks on Ramanujan graphs and complexes
Speaker, Affiliation Ori Parzanchevski, Hebrew University
Date, Time 27 February 2019, 15:45-16:45
Location HG G 43
Abstract Ramanujan graphs are finite graphs which behave (in some sense) like an infinite tree. They have remarkable properties, such as minimal mixing rate and diameter, which found applications both in computer science and in pure mathematics. Ramanujan complexes are finite simplicial complexes which behave like infinite affine buildings, or symmetric spaces for p-adic Lie groups. Random walks on these complexes present a remarkable behavior, which leads to new applications in probability, group theory, and computer science. Based on joint works with M. Chapman, S. Evra, K. Golubev, E. Lubetzky, A. Lubotzky and P. Sarnak.
Random walks on Ramanujan graphs and complexesread_more
HG G 43
6 March 2019
15:45-16:45 		Christoforos Neofytidis
Université de Genève
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Geometry Seminar

Title Self-homeomorphisms of reducible 3-manifolds and applications in topology, geometry and dynamics
Speaker, Affiliation Christoforos Neofytidis, Université de Genève
Date, Time 6 March 2019, 15:45-16:45
Location HG G 43
Abstract We recall the self-homeomorphisms of a closed oriented reducible 3-manifold. Using this description, we discuss various problems in low-dimensional topology and dynamics, such as the existence of Anosov tori in 3-manifolds and the simplicial volume of mapping tori of 3-manifolds. (Based on joint works with Shicheng Wang and Michelle Bucher respectively.)
Self-homeomorphisms of reducible 3-manifolds and applications in topology, geometry and dynamicsread_more
HG G 43
13 March 2019
15:45-16:45
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Geometry Seminar

Title No seminar, ETH hosts Current Trends in Mathematics Symposium
Speaker, Affiliation
Date, Time 13 March 2019, 15:45-16:45
Location HG G 43
No seminar, ETH hosts Current Trends in Mathematics Symposium
HG G 43
20 March 2019
15:45-16:45 		Karin Baur
University of Leeds
Details

Geometry Seminar

Title Cluster structures on Grassmannians: geometry informing algebra
Speaker, Affiliation Karin Baur, University of Leeds
Date, Time 20 March 2019, 15:45-16:45
Location HG G 43
Abstract Algebra, Geometry and Combinatorics are closely linked. Starting from classical theorems by Pythagoras and Ptolemy we will discuss the combinatorics of triangulations of surfaces and of dimer models on disks. This yields a beautiful approach to cluster algebras. Of particular interest are approaches to Grassmannian Cluster algebras with their impact on representation theory.
Cluster structures on Grassmannians: geometry informing algebraread_more
HG G 43
27 March 2019
15:45-16:45 		Adrien Boyer
Université Paris Diderot, Paris 7
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Geometry Seminar

Title Spherical functions on hyperbolic groups and property RD (Rapid Decay)
Speaker, Affiliation Adrien Boyer, Université Paris Diderot, Paris 7
Date, Time 27 March 2019, 15:45-16:45
Location HG G 43
Abstract We investigate properties of some spherical fonctions defined on hyperbolic groups using boundary representations on the Gromov boundary endowed with the Patterson-Sullivan measure class. We prove sharp decay estimates for spherical functions as well as spectral inequalities associated with boundary representations. This point of view on the boundary allows us to view the so-called property RD (Rapid Decay, also called Haagerup's inequality) as a particular case of a more general behavior of spherical functions on hyperbolic groups. If time permits, I will try to explain the idea of a constructive proof using a boundary unitary representation of a result due to de la Harpe and Jolissaint asserting that hyperbolic groups satisfy property RD.
Spherical functions on hyperbolic groups and property RD (Rapid Decay)read_more
HG G 43
17 April 2019
15:45-16:45 		Laszlo Marton Toth
EPF Lausanne
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Geometry Seminar

Title Invariant Schreier Structures on Unimodular Random Graphs
Speaker, Affiliation Laszlo Marton Toth, EPF Lausanne
Date, Time 17 April 2019, 15:45-16:45
Location HG G 43
Abstract It is a nice exercise in combinatorics to show that all finite 2d-regular graphs are Schreier graphs of the free group on d generators. We will consider the analogous question in the world of Benjamini-Schramm convergence of sparse graphs. We show that any 2d-regular unimodular random network can be given an invariant random Schreier structure. Connections to Borel combinatorics, measured group theory and Invariant Random Subgroups will also be explored. The talk aims to be self-contained, all important notions will be properly introduced.
Invariant Schreier Structures on Unimodular Random Graphsread_more
HG G 43
24 April 2019
15:45-16:45
Details

Geometry Seminar

Title Easter Break
Speaker, Affiliation
Date, Time 24 April 2019, 15:45-16:45
Location HG G 43
Easter Break
HG G 43
1 May 2019
15:45-16:45
Details

Geometry Seminar

Title Tag der Arbeit
Speaker, Affiliation
Date, Time 1 May 2019, 15:45-16:45
Location HG G 43
Tag der Arbeit
HG G 43
8 May 2019
15:45-16:45 		Roberto Frigerio
University of Pisa
Details

Geometry Seminar

Title Gromov's original approach to bounded cohomology
Speaker, Affiliation Roberto Frigerio, University of Pisa
Date, Time 8 May 2019, 15:45-16:45
Location HG G 43
Abstract In his pioneering paper "Volume and bounded cohomology"  (1982), Gromov introduced the notion of multicomplex in order to study  the bounded cohomology of topological spaces. Multicomplexes are  simplicial structures that generalize simplicial complexes without  allowing all the degeneracies appearing in simplicial sets. After developing the general homotopy theory of multicomplexes, I will  describe how multicomplexes can be exploited in the context of the  bounded cohomology. In particular, I will discuss Gromov's Mapping  Theorem (which implies that the bounded cohomology of a space only  depends on its fundamental group) and of Gromov's Vanishing Theorem,  which ensures the vanishing of the simplicial volume of closed manifolds  admitting an amenable cover of small multiplicity. If time is left, I will briefly describe further applications to the  study of the simplicial volume of open manifolds.
Gromov's original approach to bounded cohomologyread_more
HG G 43
15 May 2019
15:45-16:45 		Nora Szöke
EPF Lausanne
Details

Geometry Seminar

Title Extensive amenability and a Tits alternative for topological full groups
Speaker, Affiliation Nora Szöke, EPF Lausanne
Date, Time 15 May 2019, 15:45-16:45
Location HG G 43
Abstract A group action is called amenable if there exists an invariant mean on the space. In this talk I will present a stronger property, namely the extensive amenability of group actions. This property was introduced by Juschenko and Monod. They proved that the topological full group of a minimal Cantor Z-action is always amenable, giving the first examples of finitely generated infinite amenable simple groups. I will talk about the generalization of this result to virtually Z groups, and how it leads to a Tits alternative for topological full groups of finitely generated groups.
Extensive amenability and a Tits alternative for topological full groupsread_more
HG G 43
22 May 2019
15:45-16:45 		Virginie Charette
Université de Sherbrooke
Details

Geometry Seminar

Title Title T.B.A.
Speaker, Affiliation Virginie Charette, Université de Sherbrooke
Date, Time 22 May 2019, 15:45-16:45
Location HG G 43
Title T.B.A. (CANCELLED)
HG G 43

Organisers: Marc Burger, Manfred Einsiedler, Peter Feller, Alessandra Iozzi, Urs Lang, Viktor Schröder, Alessandro Sisto

Archive: AS 24 SS 24 AS 23 SS 23 AS 22 SS 22 AS 21 AS 20 SS 20 AS 19 SS 19 AS 18 SS 18 AS 17 SS 17 AS 16 SS 16 AS 15 SS 15 AS 14 SS 14 AS 13 SS 13 AS 12 SS 12 AS 11 SS 11 AS 10 SS 10 AS 09 SS 09

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