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2019 Apr 11

Colloquium: Ohad Feldheim - Lattice models of magnetism: from magnets to antiferromagnets

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2:30pm to 3:30pm

Location: 

Manchester Building (Hall 2), Hebrew University Jerusalem

Abstract:
The Ising model, and its generalisation, the Potts model, are two classical graph-colouring models for magnetism and antiferromagnetism. Albeit their simple formulation, these models were instrumental in explaining many real-world magnetic phenomena and have found various applications in physics, biology and computer science. While our understanding of these models as modeling magnets has been constantly improving since the early twentieth century, little progress was made in treatment of Potts antiferromagnets.
2019 May 30

Colloquium: Alon Nishry (TAU) - Zeros of random power series

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2:30pm to 3:30pm

Location: 

Manchester Building (Hall 2), Hebrew University Jerusalem

Abstract:
A central problem in complex analysis is how to describe zero sets of power series in terms of their coefficients. In general, it is difficult to obtain precise results for a given function. However, when the function is defined by a power series, whose coefficients are independent random variables, such results can be obtained. Moreover, if the coefficients are complex Gaussians, the results are especially elegant. In particular, in this talk I will discuss some different notions of "rigidity" of the zero sets.
2018 Dec 13

Erdos Lectures: Igor Pak (UCLA) - Counting integer points in polytopes

Lecturer: 

Igor Pak (UCLA)
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2:30pm to 3:30pm

Location: 

Manchester Building (Hall 2), Hebrew University Jerusalem
Given a convex polytope P, what is the number of integer points in P? This problem is of great interest in combinatorics and discrete geometry, with many important applications ranging from integer programming to statistics. From a computational point of view it is hopeless in any dimensions, as the knapsack problem is a special case. Perhaps surprisingly, in bounded dimension the problem becomes tractable. How far can one go? Can one count points in projections of P, finite intersections of such projections, etc?
2018 Oct 21

Zabrodsky Lecture 2: Cohomological Field Theories

Lecturer: 

Rahul Pandharipande (ETH Zurich)
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11:00am to 12:00pm

Location: 

Ross 70
Cohomological Field Theories (CohFTs) were introduced to keep track of the classes on the moduli spaces of curves defined by Gromov-Witten theories and their cousins. I will define CohFTs (following Kontsevich-Manin), explain the classification in the semisimple case of Givental-Teleman, and discuss the application to Pixton's relations which appear in the first lecture.
2018 Oct 18

Zabrodsky Lecture 1: Geometry of the moduli space of curves

Lecturer: 

Rahul Pandharipande (ETH Zurich)
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2:30pm to 3:30pm

Location: 

Manchester House, Lecture Hall 2

The moduli space of curves, first appearing in the work of Riemann in the 19th century, plays an important role in geometry. After an introduction to the moduli space, I will discuss recent directions in the study of tautological classes on the moduli space following ideas and conjectures of Mumford, Faber-Zagier, and Pixton. Cohomological Field Theories (CohFTs) play an important role. The talk is about the search for a cohomology calculus for the moduli space of curves parallel to what is known for better understood geometries. My goal is to give a presentation of the progress in the past decade and the current state of the field.

2019 Mar 11

Combinatorics Seminar: Yuval Filmus (Technion) "Structure of (almost) low-degree Boolean functions"

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11:00am to 1:00pm

Location: 

CS bldg, room B500, Safra campus, Givat Ram
Speaker: Yuval Filmus, Technion
Title: Structure of (almost) low-degree Boolean functions
Abstract:
Boolean function analysis studies (mostly) Boolean functions on {0,1}^n.
Two basic concepts in the field are *degree* and *junta*.
A function has degree d if it can be written as a degree d polynomial.
A function is a d-junta if it depends on d coordinates.
Clearly, a d-junta has degree d.
What about the converse (for Boolean functions)?
What if the Boolean function is only *close* to degree d?
2019 Jan 10

Joram Seminar: Larry Guth (MIT) - Introduction to decoupling

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2:30pm to 3:30pm

Location: 

Manchester Building (Hall 2), Hebrew University Jerusalem
Decoupling is a recent development in Fourier analysis. In the late 90s, Tom Wolff proposed a decoupling conjecture and made the first progress on it. The full conjecture had seemed well out of reach until a breakthrough by Jean Bourgain and Ciprian Demeter about five years ago.
Decoupling has applications to problems in PDE and also to analytic number theory. One application involves exponential sums, sums of the form
$$\sum_j e^{2 pi i \omega_j x}.$$
2018 Jun 28

Basic Notions: Barry Simon "More Tales of our Forefathers (Part II)"

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4:00pm to 5:30pm

Location: 

Manchester Hall 2
This is not a mathematics talk but it is a talk for mathematicians. Too often, we think of historical mathematicians as only names assigned to theorems. With vignettes and anecdotes, I'll convince you they were also human beings and that, as the Chinese say, "May you live in interesting times" really is a curse. Among the mathematicians with vignettes are Riemann, Newton, Poincare, von Neumann, Kato, Loewner, Krein and Noether.

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