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Colloquia & Seminars


  1. DMS Research Seminar: Stable commutator length on mapping class groups

    Location: MSRI: Simons Auditorium
    Speakers: Koji Fujiwara (Kyoto University)

    In the first part I explain the classical construction of quasi-morphisms by Brooks, a connection between quasi-morphisms and stable commutator length of a group element, scl.

    In the second part I discuss algebraic conditions for an element to have scl=0, and on the other hand, explain why negative curvature tends to imply scl>0. Combining them I give a precise condition for a mapping class to have scl >0 in terms Nielsen-Thurston classification. This is a joint work with Bestvina and Bromberg.

    Updated on Mar 20, 2015 11:42 AM PDT
  2. Minicourse

    Location: MSRI: Simons Auditorium
    Speakers: Bernhard Leeb (Ludwig-Maximilians-Universität München)

    This is a series of talks on my work with Bernhard Leeb and Joan Porti, aiming to extend the theory of geometrically finite discrete groups from rank 1 symmetric spaces to higher rank. I will start by reviewing various equivalent definitions of convex-cocompact subgroups of rank 1 Lie groups. Then I review basic geometry of higher rank symmetric spaces and their ideal boundaries. After that, I will define several notions of geometric finiteness in higher rank which generalize (some of) the rank one definitions and prove at least some of the implications between them.  My lectures will be continued by the ones by Bernhard Leeb, who will prove further equivalences of different definitions. 

    Created on Mar 23, 2015 09:57 AM PDT
  1. DMS Postdoc Seminar: Andreev's theorem on projective Coxeter polyhedra

    Location: MSRI: Simons Auditorium
    Speakers: Gye-Seon Lee (Ruprecht-Karls-Universität Heidelberg)

    In 1970, E.M. Andreev gave a full description of 3-dimensional compact hyperbolic polyhedra with dihedral angles submultiples of pi. We call them hyperbolic Coxeter polyhedra. More precisely, given a combinatorial polyhedron C with assigned dihedral angles, Andreev’s theorem provides necessary and sufficient conditions for the existence of a hyperbolic Coxeter polyhedron realizing C. Since hyperbolic geometry arises naturally as sub-geometry of real projective geometry, we can ask an analogous question for compact real projective Coxeter polyhedra. In this talk, I’ll give a partial answer to this question. This is a joint work with Suhyoung Choi.

    Created on Mar 20, 2015 11:57 AM PDT
  2. GAAHD Postdoc Seminar: Gap distributions for saddle connections on the octagon

    Location: MSRI: Simons Auditorium
    Speakers: Grace Work (University of Illinois at Urbana-Champaign)

    (Joint with Caglar Uyanik.) Following a strategy developed by Athreya and Cheung, we compute the gap distribution of the slopes of saddle connections on the octagon by translating the problem to a question about return times of the horocycle flow to an appropriate Poincaré Section. This same strategy was used by Athreya, Chaika, and Lelièvre to compute the gap distribution on the Golden L. The octagon is the first example of this type of computation where the Veech group has two cusps.

    Created on Mar 20, 2015 12:00 PM PDT
  3. 3-Manifold Seminar

    Location: 939 Evans Hall
    Speakers: Ian Agol (University of California, Berkeley)
    The topic this semester is representations of 3-manifold groups into SL_2 C. Topics will include:
     
    - character varieties and curves of characters
    - ideal points, R-tree actions, tree actions associated to ideal points of curves
    - associating incompressible surfaces to tree actions and measured laminations to R-tree actions
    - volumes of representations and Chern-Simons invariant
    - Dehn invariants, the Bloch group, and extensions
    - volume rigidity, via simplicial volume and the barycenter map
    - the A-polynomial 
     
    Created on Jan 29, 2015 09:25 AM PST
  4. Open ended seminar: Quantum ergodicity on large graphs

    Location: MSRI: Baker Board Room
    Speakers: Nalini Anantharaman (Université de Strasbourg)

    Consider a sequence of finite graphs, of fixed valency, whose size goes to infinity. Assuming their girths go to infinity and that they are expanders, Etienne Le Masson and I proved some version of the "quantum ergodicity" phenomenon : for most of the eigenfunctions $psi_j$ of the laplacian, the probability measure $|psi_j(x)|^2$ on the set of vertices is close to the uniform measure.

    I first want to sketch the published proof of this result, based on the "pseudo-differential calculus" on the regular tree, defined by Le Masson. This proof is very specific to regular graphs. 

    I then want to present a new, simpler proof, that looks as if it could, in principle, be adapted to non-regular graphs. However this extension to general graphs does not seem obvious and raises several interesting questions in ergodic theory.

    Updated on Mar 26, 2015 03:48 PM PDT
  5. Geometry and Analysis of Surface Group Representations: Introduction to Spectral Networks (II)

    Location: MSRI: Baker Board Room
    Speakers: Daniele Alessandrini (Ruprecht-Karls-Universität Heidelberg)

    I will give an introduction to the theory of Spectral Networks, developed by Gaiotto, Moore and Neitzke during their research about supersymmetry. 

    These objects have an independent interest for mathematicians, mostly in the theory of surfaces. They can be described as combinatorical objects on the surface, or, equivalently as some orbits associated to a conformal structure on the surface and a collection of holomorphic differentials.

    The main focus will be on how to use these objects to give coordinates on the moduli spaces of representations of surface groups. These coordinates generalise Fenchel-Nielsen coordinates and Fock-Goncharov coordinates in an especially intriguing way.

    Updated on Mar 26, 2015 04:16 PM PDT
  6. Lorentzian geometric structures seminar: Margulis spacetimes and contracting deformations of hyperbolic surfaces II

    Location: MSRI: Baker Board Room
    Speakers: Jeffrey Danciger (University of Texas)

    This second talk will go into more details of the proof.

    We will describe a properness criterion for free groups acting by isometries of Minkowski 3-space in terms of the deformation theory of hyperbolic surfaces. A corollary of the criterion is that every Margulis spacetime fibers in lines over a hyperbolic surface.


    We will discuss some details of the proof, including the case in which the linear part has parabolics. This talk is based on joint work with François Guéritaud and Fanny Kassel.

    Updated on Mar 26, 2015 03:39 PM PDT
  7. DMS Postdoc Seminar: Coupled Hitchin Equations

    Location: MSRI: Simons Auditorium
    Speakers: Qiongling Li (Rice University)

    In this talk, I will talk about a technical part in the joint paper with Brian Collier about studying asymptotic behavior of Hitchin representations in terms of Higgs bundles. This technical part estimates the asymptotic solution of the coupled Hitchin equations. I will also discuss how the analysis is related to geometry of frames.

    Updated on Mar 26, 2015 04:14 PM PDT
  8. GAAHD Postdoc Seminar: The stable type of the mapping class group and some relatively hyperbolic groups and applications to pointwise ergodic averages

    Location: MSRI: Simons Auditorium
    Speakers: Ilya Gekhtman (Yale University)

    The stable ratio set of a nonsingular action is a notion introduced by Bowen and Nevo to prove pointwise ergodic theorems for measure preserving actions of certain nonamenable groups.


    I  prove that stable ratio set of the action of a discrete subgroup of isometries of a CAT(-1) space with finite Bowen-Margulis measure on its boundary with the Patterson-Sullivan measure has numbers other than 0, 1 and \infinity, extending techniques of Bowen from the setting of hyperbolic groups.


    I also prove the same result for the action of the mapping class group on the sphere of projective measured foliations with the Thurston measure, using some "statistical hyperbolicity" properties for the (non hyperbolic) Teichmueller metric on Teichmueller space.

    Updated on Mar 26, 2015 03:44 PM PDT
  9. MSRI Evans Talk

    Location: 60 Evans Hall
    Speakers: Maryam Mirzakhani (Stanford University)
    Updated on Jan 15, 2015 09:40 AM PST
  10. GAAHD Research Seminar

    Location: MSRI: Simons Auditorium
    Updated on Feb 20, 2015 09:47 AM PST
  11. 3-Manifold Seminar

    Location: 939 Evans Hall
    Speakers: Ian Agol (University of California, Berkeley)
    The topic this semester is representations of 3-manifold groups into SL_2 C. Topics will include:
     
    - character varieties and curves of characters
    - ideal points, R-tree actions, tree actions associated to ideal points of curves
    - associating incompressible surfaces to tree actions and measured laminations to R-tree actions
    - volumes of representations and Chern-Simons invariant
    - Dehn invariants, the Bloch group, and extensions
    - volume rigidity, via simplicial volume and the barycenter map
    - the A-polynomial 
     
    Created on Jan 29, 2015 09:26 AM PST
  12. Open ended seminar

    Location: MSRI: Baker Board Room
    Updated on Mar 06, 2015 09:52 AM PST
  13. DMS Research Seminar

    Location: MSRI: Simons Auditorium
    Speakers: Marc Burger (Eidgenössische TH Zürich-Hönggerberg), Fanny Kassel (Université de Lille I (Sciences et Techniques de Lille Flandres Artois))
    Updated on Jan 28, 2015 02:17 PM PST
  14. GAAHD Research Seminar

    Location: MSRI: Simons Auditorium
    Updated on Feb 20, 2015 09:49 AM PST
  15. 3-Manifold Seminar

    Location: 939 Evans Hall
    Speakers: Ian Agol (University of California, Berkeley)
    The topic this semester is representations of 3-manifold groups into SL_2 C. Topics will include:
     
    - character varieties and curves of characters
    - ideal points, R-tree actions, tree actions associated to ideal points of curves
    - associating incompressible surfaces to tree actions and measured laminations to R-tree actions
    - volumes of representations and Chern-Simons invariant
    - Dehn invariants, the Bloch group, and extensions
    - volume rigidity, via simplicial volume and the barycenter map
    - the A-polynomial 
     
    Created on Jan 29, 2015 09:28 AM PST
  16. Open ended seminar

    Location: MSRI: Baker Board Room
    Updated on Mar 06, 2015 09:52 AM PST
  17. DMS Research Seminar

    Location: MSRI: Simons Auditorium
    Speakers: Marc Burger (Eidgenössische TH Zürich-Hönggerberg), Fanny Kassel (Université de Lille I (Sciences et Techniques de Lille Flandres Artois))
    Updated on Jan 28, 2015 02:16 PM PST
  18. MSRI Evans Talk

    Location: 60 Evans Hall
    Speakers: Hee Oh (Yale University)
    Updated on Jan 15, 2015 09:42 AM PST
  19. GAAHD Research Seminar

    Location: MSRI: Simons Auditorium
    Updated on Feb 20, 2015 09:49 AM PST
  20. 3-Manifold Seminar

    Location: 939 Evans Hall
    Speakers: Ian Agol (University of California, Berkeley)
    The topic this semester is representations of 3-manifold groups into SL_2 C. Topics will include:
     
    - character varieties and curves of characters
    - ideal points, R-tree actions, tree actions associated to ideal points of curves
    - associating incompressible surfaces to tree actions and measured laminations to R-tree actions
    - volumes of representations and Chern-Simons invariant
    - Dehn invariants, the Bloch group, and extensions
    - volume rigidity, via simplicial volume and the barycenter map
    - the A-polynomial 
     
    Created on Jan 29, 2015 09:29 AM PST
  21. Open ended seminar

    Location: MSRI: Baker Board Room
    Updated on Mar 06, 2015 09:51 AM PST
  22. DMS Research Seminar

    Location: MSRI: Simons Auditorium
    Speakers: Marc Burger (Eidgenössische TH Zürich-Hönggerberg), Fanny Kassel (Université de Lille I (Sciences et Techniques de Lille Flandres Artois))
    Updated on Jan 28, 2015 02:15 PM PST
  23. GAAHD Research Seminar

    Location: MSRI: Simons Auditorium
    Updated on Feb 20, 2015 09:50 AM PST
  24. Open ended seminar

    Location: MSRI: Baker Board Room
    Updated on Mar 06, 2015 09:51 AM PST
  25. DMS Research Seminar

    Location: MSRI: Simons Auditorium
    Speakers: Marc Burger (Eidgenössische TH Zürich-Hönggerberg), Fanny Kassel (Université de Lille I (Sciences et Techniques de Lille Flandres Artois))
    Updated on Jan 28, 2015 02:15 PM PST
  26. GAAHD Research Seminar

    Location: MSRI: Simons Auditorium
    Updated on Feb 20, 2015 09:52 AM PST
  27. Open ended seminar

    Location: MSRI: Baker Board Room
    Updated on Mar 06, 2015 09:50 AM PST
  28. DMS Research Seminar

    Location: MSRI: Simons Auditorium
    Speakers: Marc Burger (Eidgenössische TH Zürich-Hönggerberg), Fanny Kassel (Université de Lille I (Sciences et Techniques de Lille Flandres Artois))
    Updated on Jan 28, 2015 02:14 PM PST

Past Seminars

seminar
  1. Seminar Minicourse

    Created on Feb 23, 2015 10:43 AM PST
  2. Seminar 3-Manifold Seminar

    Created on Jan 29, 2015 09:23 AM PST
  3. Seminar Minicourse

    Created on Feb 23, 2015 10:40 AM PST
  4. Seminar 3-Manifold Seminar

    Created on Jan 29, 2015 09:22 AM PST
  5. Seminar Women in Science

    Updated on Feb 05, 2015 12:10 PM PST
  6. Seminar Minicourse

    Updated on Feb 23, 2015 10:37 AM PST
  7. Seminar 3-Manifold Seminar

    Created on Jan 29, 2015 09:21 AM PST
  8. Seminar Open ended seminar

    Updated on Mar 06, 2015 09:53 AM PST
There are more then 30 past seminars. Please go to Past seminars to see all past seminars.