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Lubotzky, Alexander (U. Jerusalem)  WPI, Seminar Room 08.135  Mon, 22. Feb 16, 9:15 
"Arithmetic quotients of the mapping class group"  
Let M=M(g) be the mapping class group of a surface of genus g > 1 (resp. M=Aut(F_g) the automorphism group of the Free group on g generators ). As it is well known, M is mapped onto the symplectic group Sp(2g,Z) (resp. the general linear group GL(g,Z) ). We will show that this is only a first case in a series: in fact, for every pair (S,r) when S is a finite group with less than g generators and r is a Qirreducible representation of S, we associate an arithmetic group which is then shown to be a virtual quotient of M. The case when S is the trivial group gives the above Sp(2g,Z) ( resp. GL(g,Z) ) but many new quotients are obtained. For example it is used to show that M(2) (resp. Aut(F_3) ) is virtually mapped onto a nonabelian free group. Another application is an answer to a question of Kowalski: generic elements in the Torelli groups are hyperbolic and fully irreducible. Joint work with Fritz Gruenwald, Michael Larsen and Justin Malestein .  

Marquis, Ludovic (U. Rennes)  WPI, Seminar Room 08.135  Mon, 22. Feb 16, 10:30 
"Projectivization of some Dehnfilling on hyperbolic 4orbifold"  
A theorem of Thurston says that if M is a finite volume noncompact hyperbolic manifold of dimension 3 (say with one cusp to simplify) then the manifold of dimension 3 obtained by filling (Dehn filling) the cusp is hyperbolic except in a finite number of cases. The hyperbolization of finite volume noncompact orbifold is possible only in dimension 2 or 3. We will exhibit examples of hyperbolic polytopes of dimension 4 which admit a projectivization of their Dehn filling. During this talk, "projectivize" will mean realise as the quotient of a properly convex open set of the real projective space by a discrete subgroup of projective transformation (preserving the convex). This is a joint work with Suhyoung Choi (KAIST) and GyeSeon Lee (Heidelberg).  

Osajda, Damian (U. Wroclaw)  WPI, Seminar Room 08.135  Mon, 22. Feb 16, 10:30 

Lee, GyeSeon (U. Heidelberg)  WPI, Seminar Room 08.135  Mon, 22. Feb 16, 13:00 
"Collar lemma for Hitchin representations"  
There is a classical result first due to Keen known as the collar lemma for hyperbolic surfaces. A consequence of the collar lemma is that if two closed curves A and B on a closed orientable hyperbolizable surface have nonzero geometric intersection number, then there is an explicit lower bound for the length of A in terms of the length of B, which holds for any hyperbolic structure on the surface. By slightly weakening this lower bound, we generalize this statement to hold for all Hitchin representations. Joint work with Tengren Zhang.  

Porti, Joan (U. Barcelone)  WPI, Seminar Room 08.135  Mon, 22. Feb 16, 14:15 
"Geometry and dynamics of Anosov representations I"  

Leeb, Bernhard (U. München)  WPI, Seminar Room 08.135  Mon, 22. Feb 16, 15:45 
"Geometry and dynamics of Anosov representations II"  

Caprace, PierreEmmanuel (U. Louvain)  WPI, Seminar Room 08.135  Tue, 23. Feb 16, 9:15 
"Linear representations of lattices in Euclidean buildings"  
When is a lattice in a Euclidean building linear? We will explain that answers to that question can be obtained by combining tools of various origins: ergodic theory, structure theory of disconnected locally compact groups, and classical theory of projective planes. Based on joint work with Uri Bader and Jean Lécureux.  

Kassel, Fanny (U. Lille)  WPI, Seminar Room 08.135  Tue, 23. Feb 16, 14:30 
"Proper affine actions for rightangled Coxeter Groups"  
We prove that any rightangled Coxeter group on k generators admits a proper affine action on R^{k(k1)/2}. This yields proper affine actions for many other groups, including all Coxeter groups. Joint work with J. Danciger and F. Guéritaud.  

Guichard, Olivier (U. Strasbourg)  WPI, Seminar Room 08.135  Tue, 23. Feb 16, 16:00 
"Symplectic Maximal Representations"  
Jointly with Anna Wienhard, we obtain a better understanding of the compact $\mathbf{R}\mathbb{P}^{2n1}$manifolds coming from maximal representations into the symplectic group $\mathrm{Sp}(2n, \mathbf{R}$, and in particular of their topology. This is based on the special properties of the boundary map into the Lagrangian variety.  

Ghosh, Sourav (U. Heidelberg)  WPI, Seminar Room 08.135  Wed, 24. Feb 16, 9:15 
"Moduli space of Margulis Spacetimes"  
In this talk I will describe the stable and unstable leaves for the geodesic flow on the space of nonwandering space like geodesics of a Margulis Spacetime. I will also describe how monodromy of Margulis Spacetimes are “Anosov representations in non semisimple Lie groups”. Finally using the Anosov property I will define the Pressure metric on the Moduli Space of Margulis Spacetimes and discuss some of its properties.  

Chatterji, Indira (U. Nice)  WPI, Seminar Room 08.135  Wed, 24. Feb 16, 10:30 
"The median class for groups acting on CAT(0) cube complexes."  
For a group acting on a CAT(0) cube complex of finite dimension, we construct a bounded cohomology class, called the median class, and show that this class is trivial if and only if there is a fixed point on the Roller compactification of the CAT(0) cube complex. As a corollary, we deduce that cocompact lattices is SL(2,R)xSL(2,R) cannot be cubulated. This is joint work with Alessandra Iozzi and Talia Fernos.  

Pansu, Pierre (U. Paris)  WPI, Seminar Room 08.135  Wed, 24. Feb 16, 12:00 
"The quasisymmetric Hölder equivalence Problem"  
What is the optimal pinching of curvature on spaces quasiisometric to complex hyperbolic spaces ? This leads to the following problem: what is the best Hölder continuity exponent for a homeomorphism of Euclidean space to a metric space quasisymmetric to the Heisenberg group, when the inverse map is assumed to be Lipschitz ? We give a partial result on this question.  

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