The seminar meets on Tuesdays, 10:50-12:00, in Math -101

This Week


Sebastien Martineau (Weizmann)

The geometry of locally infinite graphs


Fall 2016 meetings

Upcoming Meetings

Date
Title
Speaker
Abstract
Dec 6 The geometry of locally infinite graphs Sebastien Martineau (Weizmann)
Sun, Dec 11, 14:30–15:30 Percolation, Invariant Random Subgroups and Furstenberg Entropy Yair Hartman (Northwestern University)

In this talk I’ll present a joint work with Ariel Yadin, in which we solve the Furstenberg Entropy Realization Problem for finitely supported random walks (finite range jumps) on free groups and lamplighter groups. This generalizes a previous result of Bowen. The proof consists of several reductions which have geometric and probabilistic flavors of independent interests.

All notions will be explained in the talk, no prior knowledge of Invariant Random Subgroups or Furstenberg Entropy is assumed.

Past Meetings

Date
Title
Speaker
Abstract
Nov 8 Remarks on the set of values of the ergodic sums of an integer valued function Jean-Pierre Conze (Rennes)

For an ergodic measure preserving dynamical system $(X, \cal B, \mu, T)$ and a measurable function $f$ with values in $\mathbb{Z}$, we consider for $x \in X$ the set of values of the ergodic sums $S_nf(x):= \sum_0^{n-1} f(T^k x), n \geq 1$.

If $f$ is integrable with $\mu(f) > 0$, several properties of this set (from the point of view of recurrence or arithmetic sets) are simple consequences of Bourgain’s results (1989).

For example, the set ${S_nf(x), n \geq 1}$ contains infinitely many squares for a.e. $x$. If $f$ is not integrable, this property may fail, as shown by a construction of M. Boshernitzan. We give also a counter-example of an integrable centered function $f$ for which the cocycle $(S_nf(x), n \geq 1)$ is non regular and the property fails.

Nov 22 Conjugacy invariants of a $D_{\infty}$-Topological Markov chain Sieye Ryu (BGU)

Time reversal symmetry arises in many dynamical systems. In particular, it is an important aspect of dynamical systems which emerge from physical theories such as classical mechanics, thermodynamics and quantum mechanics. In this talk, we introduce the notion of a reversible dynamical system in symbolic dynamics. We investigate conjugacy invariants of a topological Markov chain which possesses an involutory reversing symmetry.