2015 Dec 29

# Dynamics lunch: Tom Gilat (HUJI): "Measure rigidity for dense' multiplicative semigroups (following Einsiedler and Fish)"

12:00pm to 1:00pm

## Location:

Manchester building, Hebrew University of Jerusalem, (Coffee lounge)
2015 Nov 24

# Dynamics & probability: Yaar Salomon (Stonybrook) "The Danzer problem and a solution to a related problem of Gowers"

2:00pm to 3:00pm

## Location:

Manchester building, Hebrew University of Jerusalem, (Room 209)
The Danzer problem and a solution to a related problem of Gowers Is there a point set Y in R^d, and C>0, such that every convex set of volume 1 contains at least one point of Y and at most C? This discrete geometry problem was posed by Gowers in 2000, and it is a special case of an open problem posed by Danzer in 1965. I will present two proofs that answers Gowers' question with a NO. The first approach is dynamical; we introduce a dynamical system and classify its minimal subsystems. This classification in particular yields the negative answer to Gowers'
2015 Dec 15

# Dynamics & probability: Omri Solan (TAU) - Divergent trajectories in SL_3(R)/SL_3(Z)

2:00pm to 4:30pm

## Location:

Manchester building, Hebrew University of Jerusalem, 209
Abstract:
2015 Nov 03

# Dynamics lunch: Or Landesberg (HUJI)

12:00pm to 1:00pm

## Location:

Manchester building, Hebrew University of Jerusalem, (Room 209)
Title: On the Mixing Property for Hyperbolic Systems [following a paper by Martine Babillot]
2015 Dec 02

# Dynamics & probability: Ron Rosenthal (ETHZ) "Local limit theorem for certain ballistic random walks in random environments"

2:00pm to 3:00pm

## Location:

Ross 70
Title: Local limit theorem for certain ballistic random walks in random environments Abstract: We study the model of random walks in random environments in dimension four and higher under Sznitman's ballisticity condition (T'). We prove a version of a local Central Limit Theorem for the model and also the existence of an equivalent measure which is invariant with respect to the point of view of the particle. This is a joint work with Noam Berger and Moran Cohen.
2015 Nov 17

# Dynamics & probability: Sebastian Donoso (HUJI), "Topological structures and the pointwise convergence of some averages for commuting transformations"

2:00pm to 3:00pm

## Location:

Manchester building, Hebrew University of Jerusalem, (Room 209)
Title: Topological structures and the pointwise convergence of some averages for commuting transformations Abstract: `Topological structures'' associated to a topological dynamical system are recently developed tools in topological dynamics. They have several applications, including the characterization of topological dynamical systems, computing automorphisms groups and even the pointwise convergence of some averages.  In this talk I will discuss some developments of this subject, emphasizing applications to the pointwise convergence of some averages.
2017 Mar 02

# Group actions seminar: David El-Chai Ben Ezra (HUJI) - The congruence subgroup problem for automorphism groups of  free meta-abelian groups

10:30am to 11:30am

2017 Nov 02

# Group actions: Remi Coulon (Rennes) - Growth gap in hyperbolic groups and amenability

10:30am to 11:30am

## Location:

hyperbolic groups and amenability
(joint work with Françoise Dal'Bo and Andrea Sambusetti) Given a finitely generated group G acting properly on a metric space X, the exponential growth rate of G with respect to X measures "how big" the orbits of G are. If H is a subgroup of G, its exponential growth rate is bounded above by the one of G. In this work we are interested in the following question: what can we say if H and G have the same exponential growth rate? This problem has both a combinatorial and a geometric origin.
2017 Apr 27

# Group actions: Yair Glasner (BGU) - On Highly transitive permutation representations of groups.

10:30am to 11:30am

## Location:

Ross 70
Abstract: A permutation representation of a group G is called highly transitive if it is transitive on k-tuples of points for every k. Until just a few years ago groups admitting such permutation representations were thought of as rare. I will focus on three rather recent papers: G-Garion, Hall-Osin, Gelander-G-Meiri (in preparation) showing that such groups are in fact very common.
2017 Dec 28

# Group actions seminar: Ilya Khayutin(IAS/Princeton)

10:30am to 11:30am

2017 Jun 29

# Special ergodic theory seminar: Abel Farkas (HUJI), Conditional measure on the Brownian path

10:00am to 11:00am

For a given deterministic measure we construct a random measure on the Brownian path that has expectation the given measure. For the construction we introduce the concept of weak convergence of random measures in probability. The machinery can be extended to more general sets than Brownian path.
2016 Nov 03

# Monodromy groups & Arithmetics groups

## Lecturer:

V.N. Venkataramana
2:30pm

## Location:

Lecture Hall 2
To a linear differential equation on the projective line with finitely many points of singularities, is associated a monodromy group; when the singularities are "reguar singular", then the monodromy group gives more or less complete information about the (asymptotics of the ) solutions.

The cases of interest are the hypergeometric differential equations, and there is much recent work in this area, centred around a question of Peter Sarnak on the arithmeticity/thin-ness of these monodromy groups. I give a survey of these recent results.
2018 Jan 07

# The 21st Midrasha in Mathematicae: Lie Theory without Groups

Sun, 07/01/2018 (All day) to Fri, 12/01/2018 (All day)