2019 Jun 04

Dynamics Seminar: Arie Levit - Surface groups are flexibly stable

12:00pm to 1:00pm

This will be a research talk. The abstract is below:
A group G is stable in permutations if every almost-action of G on a finite set is close to some actual action. Part of the interest in this notion comes from the observation that a non-residually finite stable group cannot be sofic. 
I will show that surface groups are stable in a flexible sense, that is if one is allowed to "add a few extra points" to the action. This is the first non-trivial stability result for a non-amenable group. 
2019 May 13

NT & AG Seminar: "A dream desingularization algorithm", Michael Temkin (HU)

2:30pm to 4:00pm


Ross 70
Abstract: Any birational geometer would agree that the best algorithm
for resolution of singularities should run by defining a simple invariant of
the singularity and iteratively blowing up its maximality locus.
The only problem is that already the famous example of Whitney umbrella
shows that this is impossible, and all methods following Hironaka had
to use some history and resulted in more complicated algorithms.
Nevertheless, in a recent work with Abramovich and Wlodarczyk we did
2019 May 07

Anatoly Vershik (St. Petersburg) Соmbinatorial (locally finite) еncoding of the Bernoulli processes with infinite entropy.

2:00pm to 3:00pm

The realization of m.p automorphisms as transfer on the space of the
paths on the graded graphs allows to use new kind of encoding
of one-sided Bernoulli shift.
I will start with simple example how to realize Bernoulli shift in
the locally finite space (graph) $\prod_n {1,2,\dots n}$ (triangle
Much more complicated example connected to old papers by
S.Kerov-Vershik and recent by Romik-Sniady in which one-sided
Bernoulli shift is
realized as Schutzenberger transfer on the space of infinite Young
2019 Jun 27

Group and dynamics seminar: Michael Chapman (HUJI): Cutoff on Ramanujan complexes

10:00am to 11:15am


Ross 70
Abstract: A Markov chain over a finite state space is said to exhibit the total variation cutoff phenomenon if, starting from some Dirac measure, the total variation distance to the stationary distribution drops abruptly from near maximal to near zero. It is conjectured that simple random walks on the family of $k$-regular, transitive graphs with a two sided $\epsilon$ spectral gap exhibit total variation cutoff (for any fixed $k$ and $\epsilon). This is known to be true only in a small number of cases.