Events & Seminars

2017 Dec 10

Game Theory & Math Economics: Sergiu Hart (HUJI)

4:00pm to 4:30pm

Location: 

Elath Hall, 2nd floor, Feldman Building, Edmond J. Safra Campus
A unified integral approach to all the calibration results in the literature -- from regular probabilistic calibration to smooth deterministic calibration -- using simple "hairy" fixed point and minimax results.
2017 Apr 27

Colloquium: Gal Binyamini (Weizmann), " Differential equations and algebraic points on transcendental varieties"

2:30pm to 3:30pm

Location: 

Manchester Building (Hall 2), Hebrew University Jerusalem
The problem of bounding the number of rational or algebraic points of a given height in a transcendental set has a long history. In 2006 Pila and Wilkie made fundamental progress in this area by establishing a sub-polynomial asymptotic estimate for a very wide class of transcendental sets. This result plays a key role in Pila-Zannier's proof of the Manin-Mumford conjecture, Pila's proof of the Andre-Oort conjecture for modular curves, Masser-Zannier's work on torsion anomalous points in elliptic families, and many more recent developments.
2018 May 17

Colloquium - Tzafriri lecture: Amitay Kamber (Hebrew university) "Almost-Diameter of Quotient Spaces and Density Theorems"

2:30pm to 3:30pm

Location: 

Manchester Building (Hall 2), Hebrew University Jerusalem
A recent result of Lubetzky and Peres showed that the random walk on a $q+1$-regular Ramanujan graph has $L^{1}$-cutoff, and that its “almost-diameter” is optimal. Similar optimal results were proven by other authors in various contexts, e.g. Parzanchevski-Sarnak for Golden Gates and Ghosh-Gorodnik-Nevo for Diophantine approximations. Those results rely in general on a naive Ramanujan conjecture, which is either very hard, unknown, or even false in some situations. We show that a general version of those results can be proven using the density hypothesis of Sarnak-Xue.
2017 Mar 23

Colloquium: Asaf Shapira (Tel Aviv) - "Removal Lemmas with Polynomial Bounds"

2:30pm to 3:30pm

Location: 

Manchester Building (Hall 2), Hebrew University Jerusalem
A common theme in many extremal problems in graph theory is the relation between local and global properties of graphs. We will consider the following variant of this theme: suppose a graph G is far (in some well defined sense) from satisfying property P. Must G contain a small proof of this fact? We will show that for many natural graph properties the answer is Yes. In particular, we will show that the answer is Yes whenever P is a semi-algebraic graph property, thus conforming a conjecture of Alon. Joint work with L. Gishboliner
2017 Jun 22

Colloquium: Zohovitzki prize lecture - Ariel Rapaport, "Self-affine measures with equal Hausdorff and Lyapunov dimensions"

2:30pm to 3:30pm

Location: 

Manchester Building (Hall 2), Hebrew University Jerusalem
A measure on the plane is called self-affine if it is stationary with respect to a finitely supported measure on the affine group of R^2. Under certain randomization, it is known that the Hausdorff dimension of these measures is almost surely equal to the Lyapunov dimension, which is a quantity defined in terms of the linear parts of the affine maps. I will present a result which provides conditions for equality between these two dimensions, and connects the theory of random matrix products with the dimension of self-affine measures.
2017 Jun 15

Colloquium: Alexander Logunov (Tel Aviv), "0,01% Improvement of the Liouville property for discrete harmonic functions on Z^2"

2:30pm to 3:30pm

Location: 

Manchester Building (Hall 2), Hebrew University Jerusalem
Let u be a harmonic function on the plane. The Liouville theorem claims that if |u| is bounded on the whole plane, then u is identically constant. It appears that if u is a harmonic function on a lattice Z^2, and |u| < 1 on 99,99% of Z^2, then u is a constant function.   Based on a joint work(in progress) with L.Buhovsky, Eu.Malinnikova and M.Sodin.  
2017 May 04

Colloquium: Jozsef Solymozi (UBC) Erdos Lecture Series, "The sum-product problem"

2:30pm to 3:30pm

Location: 

Manchester Building (Hall 2), Hebrew University Jerusalem
The incompatibility of multiplicative and additive structures in various fields and rings is an important phenomena. In this talk I will talk about a special case of it. Let us consider a finite subset of integers, A. The sum set of A is the set of pairwise sums of elements of A and the product set is the set of pairwise products. Erdős and Szemeredi conjectured that either the sum set or the product set should be large, almost quadratic in size of A. The conjecture is still open. Similar questions can be asked over any ring or field.
2017 Apr 20

Colloquium - Avraham (Rami) Aizenbud (Weizmann), "Representation count as a Meeting Point for Analysis, Arithmetic, Geometry and Algebra"

2:30pm to 3:30pm

Location: 

Manchester Building (Hall 2), Hebrew University Jerusalem
Consider the following questions: 1. How does the volume of the set f(x_1,...,x_d) < epsilon behaves when epsilon goes to 0? 2. How does the number of solutions of the equation f(x_1,...,x_d) = 0 (mod n) behaves when n goes to infinity. I will present these and other questions which looks as if they are taken from different areas of mathematics. I'll explain the relation between those questions. Then I'll explain how this relation is used in order to show the following theorem answering a question of Larsen and Lubotzky:
2018 May 03

Colloquium - Dvoretzki lecture 1: Alexei Borodin (MIT) - "Integrable probability"

2:30pm to 3:30pm

Location: 

Manchester Building (Hall 2), Hebrew University Jerusalem
The goal of the talk is to survey the emerging field of integrable probability, whose goal is to identify and analyze exactly solvable probabilistic models. The models and results are often easy to describe, yet difficult to find, and they carry essential information about broad universality classes of stochastic processes.
2017 Mar 16

Colloquium: Oren Becker (HUJI) Tzafriri Prize Lecture "Equations in permutations and group theoretic local testability"

2:30pm to 3:30pm

Location: 

Manchester Building (Hall 2), Hebrew University Jerusalem
Abstract: Given two permutations A and B which "almost" commute, are they "close" to permutations A' and B' which really commute? This can be seen as a question about a property the equation XY=YX. Studying analogous problems for more general equations (or sets of equations) leads to the notion of "locally testable groups" (aka "stable groups").
2017 Jun 08

Colloquium:  Vadim Kaloshin (Maryland) - "Birkhoff Conjecture for convex planar billiards and deformational spectral rigidity of planar domains"

2:30pm to 3:30pm

Location: 

Manchester Building (Hall 2), Hebrew University Jerusalem
G.D.Birkhoff introduced a mathematical billiard inside of a convex domain as the motion of a massless particle with elastic reflection at the boundary. A theorem of Poncelet says that the billiard inside an ellipse is integrable, in the sense that the neighborhood of the boundary is foliated by smooth closed curves and each billiard orbit near the boundary is tangent to one and only one such curve (in this particular case, a confocal ellipse). A famous conjecture by Birkhoff claims that ellipses are the only domains with this

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