Invitations
When  What / Where  Title of Talk 

01/2019  MiniWorkshop on "Geometric Group Theory in Bonn" MPI für Mathematik, Bonn 
Sofic approximations  what’s the problem 
When  What / Where  Title of Talk 

11/2018  Mathematisches Kolloquium Universität Regensburg 
Finitary approximations of groups and their applications 
09/2018  Summer School on Logic and Algorithms in Group Theory Hausdorff Center for Mathematics Bonn 
Stability and invariant random subgroups 
08/2018  ICM 2018  International Congress of Mathematicians Rio de Janeiro 
Finitary approximations of groups and their applications (Invited Talk  Section Topology) 
07/2018  Ktheory School Universidad Nacional de La Plata, Argentina 
Course: Algebraic Ktheory for rings of functional analytic type 
06/2018  International Conference on Manifolds, Groups and Homotopy Isle of Skye, Scotland 
Topological methods to solve equations over groups 
04/2018  "Arithmetic and Analysis" A conference on the occasion of Christopher Deninger's 60th birthday WWU Münster 
Stability, cohomology vanishing, and nonapproximable groups 
When 
What / Where 
Title of talk 


11/2017 
Action Now Wandering Seminar! 
Stability of asymptotic representations, cohomology vanishing, and nonapproximable groups 

11/2017 
Colloquium 
Topological methods to solve equations over groups 

11/2017 
Midrasha Weizmann Institute 
Laws for finite groups 

11/2017 
Lecture Course 
C*algebras and group theory 

11/2017 
Seminar Algebra 
Short laws for finite groups 

10/2017 
RTG Colloquium 
Stability of asymptotic representations, cohomology vanishing, and nonapproximable groups 

09/2017 
Workshop on Operator Algebras, Geometry, and Actions 
Stability of asymptotic representations, cohomology vanishing, and nonapproximable groups 

08/2017 
Sums of Squares  Real Algebraic Geometry and its Applications 
Positive definite functions with symmetry 

07/2017 
Von Neumann algebras and measured group theory 
Groups of finite type 

06/2017 
Summer School on KTheory and Related Fields, 
Algebraic vs. topological Ktheory 

06/2017 
Groups, Manifolds and Ktheory 
The algebraic theory of L2invariants 

05/2017 
Workshop “Approximation, deformation, quasification” 
On finitarily approximable groups 

03/2017 
Séminaire d’Algèbres d’Opérateurs, Paris, France 
L2Betti numbers of totally disconnected groups and their approximation by Betti numbers of lattices 

01/2017 
Kolloquium, TU Darmstadt, Germany 
Topological methods to solve equations over groups 
When  What / Where  Title of talk  

11/2016 
Seminar Algebra (invited by Tim Netzer) 
Topological methods to solve equations over groups  
10/2016 
Seminar Nonlinear algebra MPIMIS Leipzig, Germany (invited by Bernd Sturmfels) 
Topological methods to solve equations over groups 

07/2016 
XXI Coloquio Latinoamericano de Álgebra 
Topological methods to solve equations over groups 

06/2016 
Symposium: The mathematical legacy of Uffe Haagerup 
Groups of finite type 

06/2016 
Polish groups and geometry 
Groups of finite type 

01/2016 
Workshop Model Theory: groups, geometry, and combinatorics Oberwolfach, Germany 
Laws for finite groups 
When  What / Where  Title of talk  

11/2015 
Scottish Operator Algebras Research meeting 
1) Bounded normal generation and automatic invariant continuity 2) Quasiisometry and topological orbit equivalence of groups 

10/2015 
Arbeitsgemeinschaft: Mathematical Quasicrystals 
Danzer' Problem and topological dynamics 

08/2015 
Conference on Topology and Geometry 
Topological methods to solve equations over groups  
06/2015 
Workshop "Noncommutative Geometry" 
Noncommutative Real Algebraic Geometry 

06/2015 
Hausdorff Kolloquium 
Determinants, Entropy, and L²Torsion  
06/2015 
Growth, Symbolic Dynamics and Combinatorics of Words in Groups 
Asymptotic properties of word maps on compact simple groups 

05/2015 
Workshop on NonLinear Algebra 
Hilbert's 17th Problem 

05/2015 
NCGOA Spring Institute 2015 
Bounded normal generation and invariant automatic continuity  
05/2015 
NCGOA Spring Institute 2015 
Lecture Series: Finitedimensional approximation properties of groups and their applications  
04/2015 
Asymptotic invariants of groups 
Approximation theorems for totally disconnected groups  
03/2015 
Spring school on Algebraic Ktheory of topological algebras 
Lecture Series: Algebraic vs. topological Ktheory 

02/2015 
Generalized Cohomology 
Lecture Series: L2cohomology for locally compact groups  
01/2015 
Workshop "Geometric Topology" 
Divisibility and group laws for finite simple groups 
When  What / Where  Title of talk  

12/2014  Gruppen, Geometrie und Dynamik Gießen, Germany 
Divisibility and group laws for finite simple groups  
11/2014  Colloquium; invited by Dieter Kotschick LMU München, Germany 
Divisibility and group laws for finite simple groups  
10/2014  Arbeitsgemeinschaft: Totally Disconnected Groups Oberwolfach, Germany 
Transformation groups  
09/2014  Invited lecture series ICMAT; Madrid, Spain 
Lecture Series: Finitedimensional approximation properties of groups and their applications  
09/2014  Workshop "Topologie" Oberwolfach, Germany 
Equations over groups  
07/2014  Operator Theory 25 Timisoara, Romania 
Random walks and random invariant forests  
06/2014  Workshop on Graphs, Groups, and Probability Renyi Institute, Budapest, Hungary 
Divisibility and group laws for finite simple groups  
06/2014  Summer School on Graphs, Groups, and Probability Renyi Institute, Budapest, Hungary 
Lecture Series: Graph limits and applications to groups and group rings  
04/2014  Workshop Real Algebraic Geometry With A View Toward Systems Control and Free Positivity Oberwolfach, Germany 
NC real algebraic geometry and applications to group rings  
04/2014  Arbeitsgemeinschaft: Superrigidity Oberwolfach, Germany 
NC real algebraic geometry and applications to group rings  
02/2014  Groups acting on rooted trees and around (Conference as part of the IHP trimester on Random Walks and Asymptotic Geometry of Groups) IHP, Paris, France 
Random walks and invariant random forests  
02/2014  Séminaire Algèbres d'opérateurs JussieuPRG, Paris, France 
Determinants, Entropy, and l²Torsion  
01/2014  Algebra Seminar Glasgow, Scotland 
Equations over groups  
01/2014  Analysis Seminar Glasgow, Scotland 
Determinants, Entropy, and l²Torsion 
When  What / Where  Title of talk  

12/2013  Oberseminar Analysis, invited by Elmar Schrohe Hannover, Germany 
Determinants and Entropy  
12/2013  Colloquium, invited by Bernhard KrötzPaderborn, Germany  Determinants and Entropy  
11/2013  NRW Topologie Tagung Bonn, Germany 
Entropy, Determinants, and L2Torsion  
10/2013  Arbeitsgemeinschaft: Sofic Entropy Oberwolfach, Germany 
Sofic groups  
08/2013  Workshop "C*Algebren" Oberwolfach, Germany 
Ultraproducts of compact simple groups  
08/2013  Concentration week in Dynamics, Geometry, and Operator Algebras Texas A&M, USA 
Character rigidity and its consequences  
07/2013  Dynamical systems of algebraic origin Seattle, USA 
von Neumann algebras, Determinants, and l2Torsion  
07/2013  Von Neumann algebras and measurable group theory Leuven, Belgium 
Determinants, Entropy, and l2Torsion  
06/2013  Noncommutative Geometry and Quantum Groups at the Fields Institute Toronto, Canada 
Determinants, Entropy, and l2Torsion  
06/2013  Colloquium, invited by Martin Henk Magdeburg, Germany 
Groups and their characters  
05/2013  GeometrieSeminar, invited by Ulrich Brehm Dresden, Germany 
Was ist der Limes einer Folge von Graphen?  
04/2013  Word maps and stability of representations ESI, Vienna, Austria 
Ulam stability and character rigidity  
04/2013  Arbeitsgemeinschaft: Limits of Structures Oberwolfach, Germany 
Sofic groups and unimodular random networks 
When  What / Where  Title of talk  

11/2012  Masterclass on Sofic groups and applications to operator algebras Copenhagen, Denmark 
Lecture Series: Finitedimensional approximation properties of groups and their applications  
10/2012  Action Now, group actions, their dynamics and geometry Berlin, Germany 
Determinants, Entropy, and l2Torsion  
08/2012  GolodShafarevich Groups and Algebras and Rank Gradient ESI, Vienna, Austria 
Normal generation of groups and l²invariants  
07/2012  Colloquium of the RTG "Mathematical structures in Quantum Physics" Göttingen, Germany 
Determinants, Entropy, and l2Torsion  
05/2012  Colloquium, invited by Ulrich BrehmDresden, Germany  Determinants and Entropy  
04/2012  Geometric and Analytic Aspects of Group TheoryInstitut MittagLeffler, Stockholm, Sweden  Determinants, Entropy, and l2Torsion  
03/2012  Dynamics Seminar, invited by Alex Lubotzky and Elon Lindenstrauss Jerusalem, Israel 
Determinants, Entropy, and l2Torsion  
02/2012  Invariant random subgroups Sde Boker, Israel 
Determinants, Entropy, and l2Torsion  
02/2012  Positivity, Convexity, NCGeometry, Optimization Magdeburg, Germany 
Determinants, Entropy, and l2Torsion 
When  What / Where  Title of talk  

12/2011 
Infinite monster groups ESI, Vienna, Austria 
1) von Neumann algebras and l2invariants 2) Determinants, Entropy, and l2Torsion 

12/2011 
Sächsischer Geometrietag Chemnitz, Germany 
Hilberts 17th problem and its descendants  
11/2011 
Talk at the Institute of Mathematics Münster, Germany 
Determinants, Entropy, and l2Torsion  
11/2011 
Colloquium Regensburg, Germany 
Determinants, Entropy, and l2Torsion  
11/2011 
Noncommutative Geometry Seminar of the Mathematical Institute of the Polish Academy of Sciences Warsaw, Poland 
1) Convergent sequences in discrete groups 2) Algebraic Geometry of topological spaces 

11/2011 
Workshop on the occasion of Eberhard Kirchberg's 65th birthday Copenhagen, Denmark 
Determinants, Entropy, and l²Torsion 

09/2011 
DMV Tagung Köln, Germany 
l2Betti numbers for groups and manifolds  
09/2011 
AIM Workshop: L2 invariants and their relatives for finitely generated groups AIM, Palo Alto, California 
l2invariants and their approximation properties 

09/2011 
Conference on C*algebras and related topics RIMS, Kyoto, Japan 
l2invariants for groups and groupoids 

07/2011 
Workshop "Von Neumann algebras and ergodic theory of group actions" IHP, Paris, France 
l2Betti numbers for groups and groupoids and their applications 

06/2011 
Semester "Von Neumann algebras and ergodic theory of group actions" IHP, Paris, France 
Lecture series: Finitedimensional approximation properties of groups and their applications  
05/2011 
Workshop "Finitedimensional Approximation of Discrete Groups" Oberwolfach, Germany 
Introduction to sofic and hyperlinear groups and applications 

05/2011 
Talk at the Dept. of Mathematics TU Dresden, Germany 
Gruppen und Geometrie 

04/2011 
Noncommutative geometry Seminar, Subfactor Seminar, and Topology and Group Theory seminar Vanderbilt, Nashville, USA 
Finitedimensional approximation properties of groups 

03/2011 
Invited by David Fisher and Russell Lyons as Visiting Scholar of the Department of Mathematics Bloomington, Indiana, USA 
Finitedimensional approximation properties of groups 

03/2011  Group actions on measure spaces TAMU College Station, USA 
Extensions of discrete measured groupoids 
When  What / Where  Title of talk  

12/2010  6. Thüringer Geometrietag Jena, Germany 
Betti numbers of finite covers of compact 3manifolds  
11/2010  Kolloquium über Reine Mathematik Hamburg, Germany 
Convergent sequences in discrete groups  
11/2010  Invited Speaker at North British Functional Analysis Seminar Glasgow, Scotland 
Lecture series: Unitary representations of groups  variations on a theme  
11/2010  Conference "Ktheory, C*algebras and index theory" Göttingen, Germany 
Homotopy invariance of negative algebraic Ktheory  
09/2010  Workshop "Topologie" Oberwolfach, Germany 
Homotopy invariance of negative algebraic Ktheory  
09/2010  Workshop "Actions and Invariants of Residually Finite Groups: Asymptotic Methods" Oberwolfach, Germany 
Integrality properties of spectral measures  
09/2010  NestFest  Conference in Honor of Ryszard Nest's 60th Birthday Copenhagen, Denmark 
Convergent sequences in discrete groups  
08/2010  Talk at the Mathematical Institute Göttingen, Germany 
Convergent sequences in discrete groups  
06/2010  Noncommutative Lpspaces, Operator spaces and ApplicationsBanff, Canada  Finitedimensional approximation properties of groups and tracial algebras  
06/2010  Summer school on C*algebrasNordfjordeid, Norway  Lecture series: Unitary representations of groups  
05/2010  Talk in the Oberseminar Geometrie, MPI MISLeipzig, Germany  Convergent sequences in discrete groups  
03/2010  Talk in the Geometry Seminar ETH Zürich, Switzerland 
Stability of unitary representations  
03/2010  Workshop "C*Algebren" Oberwolfach, Germany 
Stability of unitary representations  
02/2010  Visit of the Alfred Renyi Institute of the Hungarian Academy of Sciences Budapest, Hungary 
Cocycles and l2invariants  
02/2010  Workshop about von Neumann algebras and group actions Copenhagen, Denmark 
Lecture series: Stability of unitary representations  
01/2010  Colloquium of the Mathematical Institute Münster, Germany 
Almost representations of lattices in semisimple Lie groups  
01/2010  Talk at the Dept. of MathematicsTU Dresden, Germany  Eine parametrisierte Version des Satzes von QuillenSuslin 
When  What / Where  Title of talk  

11/2009 
HIM Trimester Program on Rigidity Bonn, Germany 
Almost representations of lattices in semisimple Lie groups  
11/2009 
Colloquium of the RTGGöttingen, Germany  Almost representations of lattices in semisimple Lie groups  
09/2009 
HIM Trimester Program on Rigidity Bonn, Germany 

09/2009 
Workshop "Noncommutative Geometry" Oberwolfach, Germany 
Algebraic Ktheory and algebraic approximation 

06/2009 
Affine Isometric Actions of Discrete Groups Ascona, Switzerland 
Group Cocycles and the ring of affiliated operators 

04/2009 
Invited lecture series at the School about Noncommutative Geometry Tehran, Iran 
Lecture Series: Discrete groups, von Neumann algebras and Noncommutative Geometry  
04/2009 
Geometric Group Theory on the Gulf Coast South Padre Island, Texas 
Hyperlinear groups without the factorization property 

03/2009 
Talk at Séminaire de Géométrie et Théorie Ergodique EPFL, Switzerland 
Hyperlinear groups without factorization property 

03/2009  Talk at the DPG meetingMunich, Germany  Homological properties of quantum groups  
02/2009  Seminar Algebres d'Operateurs Paris, France 
Hyperlinear groups without factorization property 
When  What / Where  Title of talk  

11/2008  Operator algebraic aspects of quantum groups Leuven, Belgium 
Homological properties of the orthogonal quantum group A_{o}(n)  
10/2008  Workshop "Von Neumann Algebras and Ergodic Theory of Group Actions" Oberwolfach, Germany 
Hyperlinear groups without factorization property  
09/2008  Workshop on the occasion of Joachim Cuntz' sixtieth birthday Münster, Germany 
Hyperlinear groups without factorization property  
09/2008  Workshop "Topologie" Oberwolfach, Germany 
Group Cocycles and the ring of affiliated operators  
08/2008  Workshop "C*Algebras" Oberwolfach, Germany 
L2invariants and simplicity of group C*algebras  
07/2008  Talk at the Institute of Mathematics Leipzig, Germany 
Analytische Invarianten im Studium unendlicher Gruppen  
05/2008  Percolation on transitive Graphs AIM Palo Alto, California 

05/2008  Talk at the Dept. of Mathematics Bielefeld, Germany 
L2Invarianten und deren Anwendungen in der geometrischen Gruppentheorie  
04/2008  Ninth NRW Topology Meeting Münster, Germany 
Group cocycles and the subgroup structure of negatively curved groups  
03/2008  Algebra Seminar, invited by Ulrich Krähmer, Glasgow, Scotland 
Group cocycles and the subgroup structure of negatively curved groups  
02/2008  Workshop on noncommutative geometry Copenhagen, Denmark 
Group cocycles and the subgroup structure of negatively curved groups  
02/2008  Journées ''Groupes quantiques'' Strasbourg, France 
L2invariants for groups and quantum groups  
02/2008  Talk at the Dept. of Mathematics Regensburg, Germany 
Über die algebraische Eigenwertvermutung  
01/2008  21. Workshop "Foundations and Constructive Aspects of QFT" Göttingen, Germany 
Open problems in the theory of von Neumann algebras and their relation to physics 
When  What / Where  Title of talk  

11/2007  Invited by Bernhard Hanke and Dieter Kotschick, Oberseminar GeometrieLMU München, Germany  Group cocycles and the subgroup structure of negatively curved groups  
10/2007  Invited by Ulrich Bunke  Regensburg, Germany  GruppenKozykel und der Ring der affilierten Operatoren 
10/2007  Workshop on von Neumann algebras, Fields Institute  Toronto, Canada  Group Cocycles and the ring of affiliated operators 
09/2007  Workshop "Noncommutative Geometry"  Oberwolfach, Germany  Group Cocycles and the ring of affiliated operators 
08/2007  Invited lecture series at the International School on noncommutative Geometry  Chern Institute, Tianjin, China  L2Betti numbers and von Neumann algebras 
06/2007  Talk at the BornHilbertSeminar  Göttingen, Germany  Spectral properties of discrete Laplacians 
06/2007  Talk at the Joint International Meeting UMIDMV  Perugia, Italy  Rank metric completion and L²invariants 
06/2007  Conference Free Probabilities, Operator Spaces and von Neumann Algebras  IMAR, Sibiu, Romania  Sofic groups and diophantine approximation 
04/2007  2 talks at the Fachbereich Mathematik und Informatik  Münster, Germany  1) Über die algebraische Eigenwert Vermutung 2) Homotopy invariance in algebraic Ktheory 
04/2007  Invited by Yuri Tschinkel, Seminar about Algebraic and Arithmetic Geometry  IU Bremen, Germany  Sofic groups and diophantine approximation 
03/2007  Free probability and the large N limit  Berkeley, USA  Rank metric completion and L2invariants 
03/2007  Invited by Benoit Collins, OttawaCarleton Analysis Seminar  Ottawa, Canada  Sofic groups and diophantine approximation 
02/2007  Invited by Ryszard Nest  Copenhagen, Denmark  Sofic groups and diophantine approximation 
01/2007  Invited by Paul Balmer  ETH Zürich, Switzerland  Sofic groups and diophantine approximation 
When  What / Where  Title of talk  

10/2006  ECOAS 06 Georgia Tech, Atlanta, USA 
L2invariants and rank metric  
09/2006  Invited lecture series Vanderbilt Univ., USA 
Lecture series: L2invariants for groups and von Neumann algebras  
09/2006  VASBI, Satellite conference of the ICM 2006 about noncommutative Geometry Valladolid, Spain 
Comparison between algebraic and topological Ktheory  
06/2006  AIM Workshop about Free Analysis AIM Palo Alto, California, USA 
L2 cohomology for von Neumann algebras  
05/2006  Invited by C.F. Bödigheimer Bonn, Germany 
L2 cohomology for von Neumann algebras  
05/2006  Invited by Wolfgang Lück and Arthur Bartels Münster, Germany 
L2 cohomology for von Neumann algebras  
04/2006  Workshop Noncommutative Geometry BIRS Banff, Canada 
L2 cohomology for von Neumann algebras  
04/2006  Invited by Ken Dykema TAMU College Station, USA 
L2 cohomology for von Neumann algebras  
01/2006  Elliptic theory and C*algebras MRCC Bedlewo, Poland 
Homotopy invariance in algebraic Ktheory 
When  What / Where  Title of talk  

09/2005  Workshop "C*Algebren" Oberwolfach, Germany 
L2cohomology for von Neumann algebras  
05/2005  Invited by Thomas Schick Göttingen, Germany 
L2cohomology for von Neumann algebras 
When  What Where/  Title of talk  

12/2004  Invited by Guillermo Cortinas Valladolid, Spain 
Homotopy invariance in algebraic Ktheory  
11/2004  Quantum Spaces  Noncommutative Geometry Dublin, Ireland 
Algebraic Ktheory of locally convex algebras  
05/07/2004  Semestre about noncommutative Geometry and algebraic Ktheory IHP Paris, France 
About the image of the BaumConnes assembly map  
05/2004  Seminar Algebres d'Operateurs Paris, France 
Unstable homology theories and beyond Bott periodicity 
When  WhatWhere  Title of talk  

07/2003  Operator algebras Sinaia, Romania 
Bivariant homology and connective Etheory  
05/2003  Invited by Michael Puschnigg CIRM Luminy, France 
Bivariant homology and connective Etheory  
03/2003  Workshop Noncommutative Geometry BIRS Banff, Canada 
Bivariant homology and connective Etheory 
When  What / Where  Title of talk  

12/2001  Workshop "C*Algebren Oberwolfach, Germany 
Bivariant homology and connective Etheory 