Events & Seminars

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.
2015 Nov 10

Dynamics & probability: Ariel Rapaport (HUJI) " Self-affine measures with equal Hausdorff and Lyapunov dimensions"

2:00pm to 3:00pm

Location: 

Manchester building, Hebrew University of Jerusalem, (Room 209)
Title: Self-affine measures with equal Hausdorff and Lyapunov dimensions Abstract: Let μ be the stationary measure on ℝd which corresponds to a self-affine iterated function system Φ and a probability vector p. Denote by A⊂Gl(d,ℝ) the linear parts of Φ. Assuming the members of A contract by more than 12, it follows from a result by Jordan, Pollicott and Simon, that if the translations of Φ are drawn according to the Lebesgue measure, then dimHμ=min{D,d} almost surely. Here D is the Lyapunov dimension, which is an explicit constant defined in terms of A and p.
2015 Dec 17

Groups & dynamics: Robert Hough (IAS) - Mixing and cut-off on cyclic groups

12:00pm to 1:00pm

Location: 

Einstein 110
Consider a sequence of random walks on $\mathbb{Z}/p\mathbb{Z}$ with symmetric generating sets $A= A(p)$. I will describe known and new results regarding the mixing time and cut-off. For instance, if the sequence $|A(p)|$ is bounded then the cut-off phenomenon does not occur, and more precisely I give a lower bound on the size of the cut-off window in terms of $|A(p)|$. A natural conjecture from random walk on a graph is that the total variation mixing time is bounded by maximum degree times diameter squared.
2015 Nov 19

Groups & dynamics: Lei Yang (HUJI) "Equidistribution of expanding translates of curves in homogeneous spaces and Diophantine approximation"

10:00am to 11:00am

Location: 

Ross 70
Title: Equidistribution of expanding translates of curves in homogeneous spaces and Diophantine approximation. Abstract: We consider an analytic curve $\varphi: I \rightarrow \mathbb{M}(n\times m, \mathbb{R}) \hookrightarrow \mathrm{SL}(n+m, \mathbb{R})$ and embed it into some homogeneous space $G/\Gamma$, and translate it via some diagonal flow
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 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.
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.

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