Events & Seminars

2016 Dec 06

Dynamics lunch: Sasha Fish (Sydney) - Monochromatic sums and products in the natural numbers

12:00pm to 1:00pm

Location: 

Manchester building, Hebrew University of Jerusalem, (Coffee lounge)
I'll report on recent applications of the LLL to two problems in the dynamics of general countable groups. The first concerns the existence of free symbolic minimal actions; the second asks about realizations of URS's (uniformly recurrent subgroups) as stability systems. I'll then concentrate on a solution of Gabor Elek to the second problem in the case of finitely generated groups.
2017 Jan 03

Dynamics lunch: Shimon Brooks (Bar Ilan) - Sullivan’s No-Wandering Theorem for Fatou Components

12:00pm to 1:00pm

Location: 

Manchester building, Hebrew University of Jerusalem, (Coffee lounge)
I'll report on recent applications of the LLL to two problems in the dynamics of general countable groups. The first concerns the existence of free symbolic minimal actions; the second asks about realizations of URS's (uniformly recurrent subgroups) as stability systems. I'll then concentrate on a solution of Gabor Elek to the second problem in the case of finitely generated groups.
2017 Mar 28

Dynamics lunch: Ariel Rapaport

12:00pm to 1:00pm

Location: 

Manchester building, Hebrew University of Jerusalem, (Coffee lounge)
A dimension gap for continued fractions with independent digits (after Kifer, Peres and Weiss)
2017 Mar 07

Dynamics lunch: Eli Glasner (Tel Aviv):Some recent applications of Lovasz's Local Lemma to problems in topological dynamics

12:00pm to 1:00pm

Location: 

Manchester building, Hebrew University of Jerusalem, (Coffee lounge)
I'll report on recent applications of the LLL to two problems in the dynamics of general countable groups. The first concerns the existence of free symbolic minimal actions; the second asks about realizations of URS's (uniformly recurrent subgroups) as stability systems. I'll then concentrate on a solution of Gabor Elek to the second problem in the case of finitely generated groups.
2016 Nov 01

Dynamics & probability: Asaf Katz (HUJI): Mixing and sparse ergodic theorems

2:00pm to 3:00pm

Location: 

Manchester building, Hebrew University of Jerusalem, (Room 209)
We consider Bourgain's sparse ergodic theorem for systems where quantitative mixing estimates are present. Focusing on the case of the horocyclic flow, we show how to use such estimates in order to bound the dimension of the exceptional set, providing evidence towards conjectures by N. Shah, G. Margulis and P. Sarnak. Moreover we show that there exists a bound which is independent from the spectral gap. The proof uses techniques from homogeneous dynamics, automorphic representations and number theory.
2017 Jun 27

Dynamics seminar:Ohad Feldheim (Stanford): The power of two-choices in reducing discrepancy

2:00pm to 3:00pm

Consider a process in which points are assigned uniformly and independently at random on the interval [0,1]. It is a classical observation that after N points were assigned, the typical discrepancy of the empirical distribution, i.e., the maximum difference between the proportion of points on any interval and the length of that interval, is of order 1/sqrt{N}. Now consider a similar online process in which at every step an overseer is allowed to choose between two independent, uniformly chosen points on [0,1].   -- By how much can the overseer reduce the discrepancy of the selected points?
2017 Mar 07

Dynamics seminar: Erez Nesharim: Badly approximable vectors in fractals

2:00pm to 3:00pm

In ergodic dynamical systems almost every point is generic. Many times it is interesting to understand how large is the set of non-generic points. In this talk I will present a criterion for a set to have a nonempty intersection with every “regular fractal". We then apply this criterion to show that the set of badly approximable vectors with weights intersects every regular fractal, and put it in the context of diagonalizable actions on homogeneous spaces.  This talk is based on a joint work with Dzmitry Badziahin, Stephen Harrap and David Simmons.
2016 Nov 22

Dynamics & probability, Vincent Delacroix (Bordeaux): Computing Lyapunov exponents of the Teichmüller flow

2:00pm to 3:00pm

Location: 

Bet Belgia Library, Hebrew University of Jerusalem
The Teichmüller flow acts as a renormalization operator for interval exchange transformations. For this reason its properties give some insight about the dynamics of rational billiards. For example Lyapunov exponents of the Teichmüller flow are tightly related to equidistribution speed in rational billiards. Since the mid 90's M. Kontsevich and A. Zorich started computations of these exponents. After giving some motivating examples for the computation of these exponents and a brief overview of 30 years of intensive research (including works of
2016 Dec 06

Dynamics & probability: Lucia Simonelli - Absolutely Continuous Spectrum for Parabolic Flows/Maps

2:00pm to 3:00pm

Location: 

Manchester building, Hebrew University of Jerusalem, (Room 209)
This talk will discuss some recent developments in the study of the spectral properties of parabolic flows and maps. More specifically, it will focus on the techniques used to determine the spectrum of the time-changes of the horocycle flow and and the effort to generalize these methods to create conditions under which a general parabolic flow/map would be expected to have absolutely continuous spectrum.
2017 May 16

Dynamics seminar: Karoly Simon (Budepest): Singularity of self-similar measures (Joint with Lajos Vago)

2:00pm to 3:00pm

We consider self-similar  Iterated Function System (IFS) on the line constructed with overlapping cylinders. Recently there have been a number of outstanding results which have suggested that the overlap has dramatic change in the most important properties of the IFS only if there is an exact overlap between some of the cylinders. In this talk, we point out that this is not always the case, at least as far as the absolute continuity of self-similar measures is concerned. Namely, we present some one-parameter families of homogeneous self- similar measures on the line such that
2017 Jan 03

Dynamics & probability: Alon Nishry (U. Michigan): Gaussian complex zeros on the hole event: the emergence of a forbidden region

2:00pm to 3:00pm

Location: 

Manchester building, Hebrew University of Jerusalem, (Room 209)
Consider the Gaussian Entire Function (GEF) whose Taylor coefficients are independent complex-valued Gaussian variables, and the variance of the k-th coefficient is 1/k!. This random Taylor series is distinguished by the invariance of its zero set with respect to the isometries of the complex plane.
2017 Jun 20

Dynamics seminar:Naomi Feldheim (Stanford): Persistence of Gaussian Stationary Processes

2:00pm to 3:00pm

Consider a real Gaussian stationary process, either on Z or on R. That is, a stochastic process, invariant under translations, whose finite marginals are centered multi-variate Gaussians. The persistence of such a process on [0,N] is the probability that it remains positive throughout this interval. The relation between the decay of the persistence as N tends to infinity and the covariance function of the process has been investigated since the 1950s with motivations stemming from probability, engineering and mathematical physics. Nonetheless, until recently, good estimates were

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