Geometry/Topology Seminar

Spring 2018

Thursdays (and sometimes Tuesdays) 3-4pm, in Ryerson 358

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• 10/11/18
• 10/18/18
• 10/25/18
• 11/01/18
• 11/08/18
• 11/15/18
• 11/29/18
• 1/10/19
• 02/28/19

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• contacts

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• previous quarters
• S2018
• W2018
• F2017
• S2017
• W2017
• F2016
• S2016
• W2016
• F2015
• S2015
• W2015
• F2014
• S2014
• W2014
• F2013
• S2013
• W2013
• F2012
• S2012
• W2012
• F2011
• S2011
• W2011
• F2010
• S2010
• W2010
• F2009
• S2009
• W2009
• F2008
• S2008
• W2008
• F2007
• S2007
• W2007
• F2006
• S2006
• W2006

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• • Thursday October 11 at 3-4pm in Ry 358
  • Rita Gitik, University of Michigan
  • On Tame Subgroups of Finitely Presented Groups
  • Abstract: We describe several examples of tame subgroups of finitely presented groups and prove that the fundamental groups of certain finite graphs of groups are locally tame.
• • Thursday October 18 at 3-4pm in Ry 358
  • Daniel Ramras, IUPUI
  • Homological stability for spaces of representations
  • Abstract: I will discuss recent work with Mentor Stafa on homological stability for various spaces built from commuting elements in Lie groups. These results depend on rational models for these spaces due to T. Baird, and utilize J. Wilson's theory of FI_W-modules. A key aspect of this work is the relationship between stability in ordinary and in equivariant (co)homology. Time permitting, I'll also discuss what is known regarding stability for character varieties of free groups and surface groups.
• • Thursday October 25 at 3-4pm in Ry 358
  • Daniel Studenmund, Notre Dame
  • Commensurability growth of nilpotent groups
  • Abstract: A classical area of study in geometric group theory is subgroup growth, which counts the number of subgroups of a given group Gamma as a function their index. We will study a richer function, the commensurability growth, associated to a subgroup Gamma in an ambient group G. The main result of this talk concerns the case that Gamma is an arithmetic subgroup of a unipotent group G, starting with the simplest example of the integers in the real line. This is joint work with Khalid Bou-Rabee.
• • Thursday November 01 at 3-4pm in Ry 358
  • Yulan Qing, University of Toronto
  • Loops with Large Twist Get Short Along Quasi-geodesics in Out(Fn)
  • Abstract: We study the behaviour of quasi-geodesics in Out(Fn) equipped with word metric. Given an element \phi of Out(Fn), there are several natural paths connecting the origin to \phi in Out(Fn). We show that these paths are, in general, not quasi-geodesics in Out(Fn). In fact, we clear up the current misunderstanding about distance estimating in Out(Fn) by showing that there exists points in Out(Fn) where all quasi-geodesics between them backtracks in all of the current Out(Fn) complexes .
• • Thursday November 08 at 3-4pm in Ry 358
  • Kevin Schreve, University of Chicago
  • Action Dimension of Simple Complexes of Groups
  • Abstract: The action dimension of a discrete group G is the minimal dimension of contractible manifold that admits a properly discontinuous G action. I will compute the action dimension of several examples,including Artin groups, graph products, and hyperplane arrangements.
• • Thursday November 15 at 3-4pm in Ry 358
  • Trevor Hyde, University of Michigan
  • Moduli of multivariate irreducible polynomials and liminal reciprocity
  • Abstract: I will share some recent results on the moduli space of multivariate polynomials which are irreducible over a field K, including a surprising connection between univariate polynomials and the limiting space of irreducibles in infinitely many variables.
• • Thursday November 29 at 3-4pm in Ry 358
  • Fedor Manin, Ohio State University
  • Geometric shadows of rational homotopy theory
  • Abstract: Given compact simplicial complexes or Riemannian manifolds X and Y, what is the least Lipschitz constant of a nullhomotopy of an L-Lipschitz map X \to Y, as a function of L? If X is the circle, then this is certainly bounded below by the square root of the Dehn function of \pi₁(Y), which for certain Y grows faster than any computable function. On the other hand, if Y is simply connected, then for any X whatsoever the answer is O(L²) (this is almost sharp in some cases.) This, among other results, follows from a geometric upgrade to a fundamental correspondence in algebraic topology due to Sullivan, which I will attempt to describe.
• • Thursday January 10 at 3-4pm in Ry 358
  • Izzet Coskun, UIC
  • TBA
  • Abstract: TBA
• • Thursday February 28 at 3-4pm in Ry 358
  • Asaf Katz, Chicago
  • TBA
  • Abstract: TBA

Due to the high number of requests, we are no longer accepting speakers via self-invitations.

For questions, contact

• Benson Farb, farb at math.uchicago.edu
• Alex Eskin, eskin at math.uchicago.edu
• Shmuel Weinberger, shmuel at math.uchicago.edu
• Howard Masur, masur at math.uchicago.edu
• Danny Calegari, dannyc at math.uchicago.edu
• Maxime Bergeron, mbergeron at math.uchicago.edu
• Nate Harman, nharman at math.uchicago.edu
• Kasia Jankiewicz, kasia at math.uchicago.edu
• Kevin Schreve, kschreve at math.uchicago.edu