Events & Seminars

2015 Nov 03

Dynamics lunch: Or Landesberg (HUJI)

12:00pm to 1:00pm


Manchester building, Hebrew University of Jerusalem, (Room 209)
Title: On the Mixing Property for Hyperbolic Systems [following a paper by Martine Babillot]
2017 Nov 02

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

10:30am to 11:30am


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


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. 
2016 Nov 03

Monodromy groups & Arithmetics groups


V.N. Venkataramana


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.