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
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.
2017 Dec 07

# Groups & dynamics: Doron Puder (TAU)

10:30am to 11:30am

2017 Oct 31

# Dynamics lunch seminar: Zemer Kosloff (HUJI) "On the Asymptotics of the ranges of random walks, following Kesten-Spitzer, Erdos-Taylor and Flatto and perhaps more"

12:00pm to 1:00pm

## Location:

Manchester faculty club
2015 Dec 08

# Dynamics lunch: Elchanan Mossel (UPenn): What do physicists mean when they talk about replica symmetry breaking - some ideas from the proof of the k satisfiability threshold conjecture.

12:00pm to 1:00pm

## Location:

Manchester building, Hebrew University of Jerusalem, (Coffee lounge)
2018 Jan 16

# Dynamics Lunch: Nishat Chnadgotia (TAU) "The periodic tiling conjecture."

12:00pm to 1:00pm

2016 Nov 15

# Dynamics lunch: Mike Hochman (HUJI)

12:00pm to 1:00pm

2018 Jan 23

# Dynamics Lunch: Naomi Feldheim (Weizmann) "How to compute the expected number of zeroes of a random function"

12:00pm to 1:00pm

## Location:

Manchester building lobby

This talk is devoted to the "Kac-Rice formula", which is an explicit way to compute
the expected number of zeroes of a random series with independent Gaussian coefficients.
We will discuss the original proofs of Kac and Rice (1940's),
an elegant geometrical proof due to Edelman and Kostlan (1995), some interesting examples,
and extensions to complex zeroes and eigenvalues of random matrices.
2017 Nov 14

# Dynamics Lunch: Rene Ruhr (TAU) "Mixing of all orders of Lie group actions"

12:00pm to 1:00pm

2017 Nov 07

# Dynamics lunch seminar: Jakub Konieczny (HUJI) "Monochromatic sums and products"

12:00pm to 1:00pm

## Location:

Manchester faculty lounge
Abstract:
2017 Nov 28

# Dynamics lunch: Benjy Weiss "Rigidity sequences for weakly mixing transformations"

12:00pm to 1:00pm

Here is a title and abstract for the lunch seminar:
Rigidity sequences for weakly mixing transformations
Abstract: I will present a recent result of Bassam Fayad
and Jean-Paul Thouvenot that shows that any rigidty
sequence for an irrational rotation is also a rigidity
sequence for some weakly mixing transformation.
2015 Nov 10

# Dynamics lunch: Lei Yang (HUJI) "Proper affine actions and geodesic flows of hyperbolic surfaces"

12:00pm to 1:00pm

## Location:

Manchester building, Hebrew University of Jerusalem, (Coffee Lounge)
Title: Proper affine actions and geodesic flows of hyperbolic surfaces