Eventss

2018 Oct 21

Zabrodsky Lecture 2: Cohomological Field Theories

Lecturer: 

Rahul Pandharipande (ETH Zurich)
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)
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"

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

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)"

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.
2018 Jun 27

Eshnav: Dr. Shaul Zemel : "From sequences of numbers to Fermat's last theorem"

Lecturer: 

Dr. Shaul Zemel
6:00pm to 7:15pm

Location: 

Manchester House, Lecture Hall 2

ד"ר שאול זמל : מסדרות מספרים ועד המשפט האחרון של פרמה

אחת הדרכים להבין התנהגויות של סדרות מספרים היא לנתח את הפונקציה היוצרת שלהם. זה מועיל במיוחד במקרה שהפונקציה הזאת נמצאת במרחב וקטורי ממימד סופי קטן. נדגים זאת במקרה פשוט, ואז נתאר סדרות מספרים המתקבלות מתבניות מודולריות. 
נראה איך מקבלים מכך כמה יחסים מעניינים, ונסיים בתיאור כללי של מה באמת הוכיח אנדרו ויילס, כשהשלים את הוכחת המשפט האחרון של פרמה.

2018 Jun 26

Amitsur Symposium: Lev Glebsky - "Approximations of groups by finite and linear groups"

4:30pm to 5:30pm

Location: 

Manchester House, Lecture Hall 2
The sofic groups and hyperlinear groups are groups approximable by finite symmetric
and by unitary groups, respectively. I recall their definitions and discuss why those classes of groups are interesting. Then I consider approximations by other classes of groups and review some results, including rather recent ones by N. Nikolov, J. Schneider, A.Thom, https://arxiv.org/abs/1703.06092 .
If time permits I'll speak about stability and its relations with approximability.
2018 Jun 26

Amitsur Symposium: Arye Juhasz - "On the center of Artin groups"

2:00pm to 3:00pm

Location: 

Manchester House, Lecture Hall 2
Let A be an Artin group. It is known that if A is spherical (of finite type) and irreducible (not a direct sum), then it has infinite cyclic center.
It is conjectured that all other irreducible Artin groups have trivial center. I prove this conjecture under a stronger assumption that not being spherical namely, if there is a standard generator which is not contained in any 3-generated spherical standard parabolic subgroup. The main tool is relative presentations of Artin groups.
2018 Jun 27

Amitsur Symposium: Yael Algom-Kfir - "The metric completion of an asymmetric metric space"

4:30pm to 5:30pm

Location: 

Manchester House, Lecture Hall 2
The Teichmuller space with the Thurston metric and Outer Space with the Lipschitz metric are two examples of spaces with an asymmetric metric i.e. d(x,y)
eq d(y,x). The latter case is also incomplete: There exist Cauchy sequences that do not have a limit. We develop the theory of the completion of an asymmetric space and give lots of examples. Time permitting we will describe the case of Outer Space.
2018 Jun 26

Amitsur Symposium: Alex Lubotzky - "First order rigidity of high-rank arithmetic groups"

10:00am to 11:00am

Location: 

Manchester House, Lecture Hall 2
The family of high rank arithmetic groups is a class of groups playing an important role in various areas of mathematics.
It includes SL(n,Z), for n>2 , SL(n, Z[1/p] ) for n>1, their finite index subgroups and many more.
A number of remarkable results about them have been proven including; Mostow rigidity, Margulis Super rigidity and the Quasi-isometric rigidity.
2018 Jun 27

Amitsur Symposium: Chloe Perin - "Forking independence in the free group"

2:00pm to 3:00pm

Location: 

Manchester House, Lecture Hall 2
Model theorists define, in structures whose first-order theory is "stable" (i.e. suitably nice), a notion of independence between elements. This notion coincides for example with linear independence when the structure considered is a vector space, and with algebraic independence when it is an algebraically closed field. Sela showed that the theory of the free group is stable. In a joint work with Rizos Sklinos, we give an interpretation of this model theoretic notion of independence in the free group using Grushko and JSJ decompositions.

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