Eventss

2019 Nov 20

Logic Seminar - Christian d'Elbée

11:00am to 1:00pm

Location: 

Ross building - Room 63

Christian d'Elbée will speak about generic generic abelian varieties.

Generic generic abelian varieties.

Abstract: 
I will present work in progress in a new NSOP1 nonsimple theory: the expansion of an abelian variety by a generic subgroup, under some conditions on the endomorphism ring.  
2019 Nov 28

Konstantin Golubev   (ETH) - On non-autocorrelated functions on a hyperbolic surface

10:00am to 11:00am

Location: 

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

Basic Notions: Jake Solomon "Enumerative geometry over an arbitrary field"

4:00pm to 5:30pm

Location: 

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.
2019 Nov 14

Basic Notions: Jake Solomon (HUJI), "Enumerative geometry over an arbitrary field"

Repeats every week every Thursday, 2 times .
4:00pm to 5:15pm

4:00pm to 5:15pm

Location: 

Ross Building, Room 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

Colloquium: Gil Kalai (HUJI) - Some recent advances in combinatorics

2:30pm to 3:30pm

Location: 

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 28

Basic Notions: Eran Nevo (HUJI) "Algebraic Combinatorics a la Stanley".

4:00pm to 5:15pm

Location: 

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.)   

2020 Jan 29

Geodesic triangles in the hyperbolic plane: Rita Gitik, University of Michigan

Lecturer: 

Rita Gitik
12:00pm to 2:00pm

Location: 

Ross 70
Abstract: Let M be an orientable hyperbolic surface without boundary and let c be a closed geodesic in M.
We prove that any side of any triangle formed by distinct lifts of c in the hyperbolic plane is shorter than c.
The talk will be presented for advanced undergraduate and beginning graduate students.
2019 Nov 11

NT & AG Lunch: Michael Temkin, "Resolution of singularities, II"

1:00pm to 2:00pm

Location: 

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.

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