2017
Dec
07

# Groups & dynamics: Doron Puder (TAU)

10:30am to 11:30am

2017
Dec
07

10:30am to 11:30am

2015
Dec
03

10:00am to 11:20am

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

10:00am to 11:00am

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
of $\mathbb{N}^2$ and $\mathbb{N}^3$ satisfying combinatorial properties.

2017
Oct
31

2017
Nov
14

2017
Nov
07

2017
Nov
28

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

12:00pm to 1:00pm

Manchester building, Hebrew University of Jerusalem, (Coffee Lounge)

Title: Proper affine actions and geodesic flows of hyperbolic surfaces

2018
Jan
09

12:00pm to 1:00pm

We will review a Breiman type theorem for Gibbs measures due to Gurevich and Tempelman. For a translation invariant Gibbs measure on a suitable translation invariant configuration set X \subset S^G, where G is an amenable group and S is a finite set, we will prove the convergence of the Shannon-McMillan-Breiman ratio on a specific subset of "generic" configurations. Provided that the above Gibbs measure exists, we also prove the convergence in the definition of pressure and the fact that this Gibbs measure is an equilibrium state.

2015
Dec
15

2018
Jan
02

12:00pm to 1:00pm

An M-dependent process X(n) on the integers, is a process for which every event concerning with X(-1),X(-2),... is independent from every event concerning with X(M),X(M+1),...
Such processes play an important role both as scaling limits of physical systems and as a tool in approximating other processes.
A question that has risen independently in several contexts is:
"is there an M dependent proper colouring of the integer lattice for some finite M?"

2017
Jun
06

12:00pm to 1:00pm

Manchester building, Hebrew University of Jerusalem, (Coffee lounge)

A dimension gap for continued fractions with independent digits (after Kifer, Peres and Weiss)

2017
Dec
05

12:00pm to 1:00pm

Abstract: It was noticed in the 30's by Doeblin & Forte that Markov
operators with "chains with complete connections"
act quasi-compactly on the Lipschitz functions. These are operators
like the transfer operators of certain expanding
C^2 interval maps (e.g. the square of Gauss map).
It is folklore that stochastic processes generated by smooth
observables under these maps satisfy many of the results
of "classical probability theory" (e.g. CLT, Chernoff inequality).
I'll try to explain some of this in a "lunchtime" mode.

2017
Nov
21

2017
Oct
24