Events & Seminars

2015 Dec 03

Groups & dynamics: Shmuel Weinberger (Chicago) - Borel and the symmetry of locally symmetric manifolds. I

10:00am to 11:20am

Location: 

Ross building, Hebrew University of Jerusalem, (Room 70)
Abstract: Borel studied the topological group actions that are possible on locally symmetric manifolds. In these two talks, I will explain Borel's work and interpret these results as a type of rigidity statement very much related to the well-known Borel conjecture of high dimensional topology. In particular, I will give the characterization of locally symmetric manifolds (of dimension not 4) which have a unique maximal conjugacy of finite group of orientation preserving homeomorphisms, due to Cappell, Lubotzky and myself. We will then
2017 May 25

Group actions/dynamics seminar: Sebastián Donoso (University of O'Higgins, Chile) Quantitative multiple recurrence for two and three transformations

10:00am to 11:00am

Location: 

Ross 70
In this talk I will provide some counter-examples for quantitative multiple recurrence problems for systems with more than one transformation.  For instance, I will show that there exists an ergodic system $(X,\mathcal{X},\mu,T_1,T_2)$ with two commuting transformations such that for every $\ell < 4$ there exists $A\in \mathcal{X}$ such that  \[ \mu(A\cap T_1^n A\cap T_2^n A) < \mu(A)^{\ell} \]  for every $n \in \mathbb{N}$.  The construction of such a system is based on the study of ``big'' subsets of $\mathbb{N}^2$ and $\mathbb{N}^3$  satisfying combinatorial properties.  
2017 Dec 21

Groups & Dynamics: Jeremy Kahn (Brown University) - Surface Subgroups in Nonuniform Lattices

10:30am to 11:30am

Location: 

Ross 70
Abstract: In 2009 the speaker and Vladimir Markovic constructed nearly geodesic surfaces in a given closed hyperbolic 3-manifold M. The construction proceeded by taking all "good pants" in M and matching them at their boundaries to produce a closed surface. I will describe this construction, as well as a new construction with Alexander Wright, of a nearly geodesic surface in the case where M has a cusp. If time permits, I will discuss the potential applications of this construction to higher rank nonuniform lattices and mapping class groups.
2015 Dec 10

Groups & dynamics: Shmuel Weinberger (Chicago) - Borel and the symmetry of locally symmetric manifolds. II

10:00am to 11:00am

Location: 

Ross building, Hebrew University of Jerusalem, (Room 70)
Abstract Borel studied the topological group actions that are possible on locally symmetric manifolds. In these two talks, I will explain Borel's work and interpret these results as a type of rigidity statement very much related to the well-known Borel conjecture of high dimensional topology. In particular, I will give the characterization of locally symmetric manifolds (of dimension not 4) which have a unique maximal conjugacy of finite group of orientation preserving homeomorphisms, due to Cappell, Lubotzky and myself. We will then
2018 Jan 04

Group actions seminar: Ilya Khayutin (IAS/Princeton) - Joint Equidistribution of CM Points

10:30am to 11:30am

Location: 

Ross 70
A sequence of Picard/Galois orbits of special points in a product of arbitrary many modular curves is conjectured to equidistribute in the product space as long as it escapes any closed orbit of an intermediate subgroup. This conjecture encompasses several well-known results and conjectures, including Duke's Theorem, the Michel-Venkatesh mixing conjecture and the equidistribution strengthening of André-Oort in this setting.

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