2020
Feb
04

# (no talk)

12:00pm to 1:00pm

Edmond J. Safra Campus The Hebrew University of Jerusalem

2020
Feb
04

12:00pm to 1:00pm

2019
Nov
28

10:00am to 11:00am

Ross 70

An L^2-function on a finite volume hyperbolic surface is called non-autocorrelated if it is perpendicular to its image under A_r, the operator of averaging over the circle of radius r, where r is fixed. We show that the support of such a function is small, namely, it takes not more than (r+1) / exp(r/2) of the volume of the surface. In my talk, I'll prove this result, and show its connection to the equidistribution of the circle on a surface (proved by Nevo).

2019
Nov
14

4:00pm to 5:30pm

Ross 70

Counting problems in algebraic geometry over an algebraically closed field have been studied for centuries. More recently, it was discovered that there are interesting counting problems over the real numbers. Topology took the place of algebraic closedness. However, the question remained whether there are interesting counting problems over more general fields where the tools of classical topology are not available. I will describe some results in this direction.

2020
Jan
23

2:30pm to 3:30pm

Manchester Building (Hall 2), Hebrew University Jerusalem

I will discuss some recent advances in combinatorics, among them the disproof of Hedetniemi conjecture by Shitov, the proof of the sensitivity conjecture by Huang, the progress on the Erdos-Rado sunflower conjecture by Alweiss, Lovett, Wu, and Zhang, and the progress on the expectation threshold conjecture by Frankston, Kahn, Narayanan, and Park.

2019
Nov
13

11:00am to 1:00pm

Ross building - Room 63

2019
Nov
28

4:00pm to 5:15pm

Ross 70

The basic idea is to associate with a combinatorial object Xan algebraic structure A(X), and derive from algebraic properties of A(X)combinatorial consequences for X. For example, Stanley's proof of the UpperBound Theorem for simplicial spheres uses the Cohen-Macaulay property of theface ring associated with a simplicial complex.

We will review the basics of Stanley's theory, illustrate themon examples, and time permitting, discuss more recent advances of this theory.

(All needed terms and background will be given in thetalk.)

2019
Nov
11

1:00pm to 2:00pm

Mathematics, Faculty Lounge

This semester will be devoted to resolution of singularities -- a process that modifies varieties at the singular locus so that the resulting variety becomes smooth. For many years this topic had the reputation of very technical and complicated, though rather elementary.

In fact, the same resolution algorithm can be described in various settings, including schemes, algebraic varieties or complex analytic spaces.

In fact, the same resolution algorithm can be described in various settings, including schemes, algebraic varieties or complex analytic spaces.

2020
Jan
28

2:00pm to 3:00pm

Ross 70

Abstract: I will explain what measure distal transformations are

and describe some new constructions obtained with Eli Glasner.

These answer, inter alia, a question recently raised by Ibarlucia and Tsankov

concerning the existence of strongly ergodic non compact distal actions of the

free group.

2019
Dec
03

2:00pm to 3:00pm

Ross 70

Gibbs measures vs. random walks in negative curvature

The ideal boundary of a negatively curved manifold naturally carries two types of measures.

On the one hand, we have conditionals for equilibrium (Gibbs) states associated to Hoelder potentials; these include the Patterson-Sullivan measure and the Liouville measure. On the other hand, we have stationary measures coming from random walks on the fundamental group.

The ideal boundary of a negatively curved manifold naturally carries two types of measures.

On the one hand, we have conditionals for equilibrium (Gibbs) states associated to Hoelder potentials; these include the Patterson-Sullivan measure and the Liouville measure. On the other hand, we have stationary measures coming from random walks on the fundamental group.

2019
Dec
02

10:00am to 12:00pm

C-400, CS building

A long-standing open problem, known as Hadwiger’s covering problem, asks what is the smallest natural number N(n) such that every convex body in R^n can be covered by a union of the interiors of N(n) of its translates.

In this talk, I will discuss some history of this problem and its close relatives, and present more recent results, including a general upper bound for N(n).

2019
Dec
09

10:00am to 12:00pm

C-400, CS building

I will describe property testing of (di)graph properties in bounded degree graph models, and talk about a characterization of the 1-sided error testable monotone graph properties and the 1-sided error testable hereditary graph properties in this model. I will introduce the notion of configuration-free properties and talk about some graph theoretic open problems.

2019
Nov
04

10:00am to 12:00pm

CS building, C-400

Title: Combinatorics and geometry in non-commutative algebraic geometry

Abstract:

Abstract:

2019
Dec
16

10:00am to 12:00pm

C-400, CS building

2019
Nov
14

10:00am to 11:00am

Ross 70

Abstract: When are two elements in a given group conjugate? We solve this problem for the group of tree almost-automorphisms. These are homeomorphisms of the tree boundary which locally look like tree automorphisms. The solution is tied with the dynamics of the group action on the tree boundary. This work is joint with W. Lederle.

2019
Nov
12

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