Seminars

2016 Nov 28

NT&AG: Boris Zilber (University of Oxford), "On algebraically closed field of characteristic 1"

2:00pm to 3:00pm

Location: 

Ros Building, 70A
Abstract: I will start with a motivation of what algebraic (and model-theoretic) properties an algebraically closed field of characteristic 1 is expected to have. Then I will explain how these properties can be obtained by the well-known in model theory Hrushovski's construction and then formulate very precise axioms that such a field must satisfy. The axioms have a form of statements about existence of solutions to systems of equations in terms of a 'multi-dimansional' valuation theory and the validity of these statements is an open problem to be discussed.
2017 Apr 03

NT&AG: Izzet Coskun (University of Illinois at Chicago), "Birational geometry of moduli spaces of sheaves on surfaces"

4:00pm to 5:00pm

Location: 

Tel Aviv University, Schreiber building, 209
Abstract: In the last five years Bridgeland stability has revolutionized our understanding of the geometry of moduli spaces of sheaves on surfaces, allowing us to compute ample and effective cones and describe different birational models. In this talk, I will survey some of my joint work with Daniele Arcara, Aaron Bertram, Jack Huizenga and Matthew Woolf on the birational geometry of moduli spaces of sheaves on the plane. I will describe the ample and effective cones of these moduli spaces, concentrating on Hilbert schemes of points and concrete examples.
2015 Dec 22

Number theory: Alexei Entin (Stanford) "Monodromy of Hurwitz spaces and extensions of F_q(t)"

10:30am to 11:45am

Location: 

Ross Building, room 70A
Hurwitz spaces are moduli spaces for extensions of curves with prescribed ramification types. They arise naturally when enumerating extensions of global function fields and also in many other contexts. The classical Hurwitz space H_{m,n} may be viewed as a finite cover of the space of n-sets of points on P^1. We will show that this cover has a big monodromy group for n>4. This can be applied to study the statistics of extensions of F_q(t) with varying branching locus in the large q limit. Joint work with Chris Hall and Robert Guralnick.
2016 Feb 22

Combinatorics

Repeats every week every Monday until Sun Feb 28 2016 .
10:30am to 12:30pm

Location: 

B221 Rothberg (CS and Engineering building)
Speaker: Asaf Nachmias (TAU) Title: The connectivity of the uniform spanning forest on planar graphs Abstract: The free uniform spanning forest (FUSF) of an infinite connected graph G is obtained as the weak limit uniformly chosen spanning trees of finite subgraphs of G. It is easy to see that the FUSF is supported on spanning graphs of G with no cycles, but it need not be connected. Indeed, a classical result of Pemantle ('91) asserts that when G=Z^d, the FUSF is almost surely a connected tree if and only if d=1,2,3,4.
2015 Nov 09

Combinatorics seminar

Repeats every week every Monday until Mon Nov 23 2015 .
11:00am to 1:00pm

11:00am to 1:00pm

Location: 

B221 Rothberg (CS and Engineering building)
Speaker: Clara Shikhelman, TAU Title: Many T copies in H-free graphs. Abstract: For two graphs T and H and for an integer n, let ex(n,T,H) denote the maximum possible number of copies of T in an H-free graph on n vertices. The study of this function when T=K_2 (a single edge) is the main subject of extremal graph theory. We investigate the general function, focusing on the cases of triangles, complete graphs and trees. In this talk the main results will be presented as will sketches of proofs of some of the following: (i) ex(n,K_3,C_5) < (1+o(1)) (\sqrt 3)/2 n^{3/2}.
2015 Nov 19

Special Combinatorics seminar: Horst Martini (TU Chemnitz, Germany), "Discrete Geometry in Minkowski Spaces"

12:00pm to 1:00pm

Location: 

Rothberg B314
Title: Discrete Geometry in Minkowski Spaces Abstract: In recent decades, many papers appeared in which typical problems of Discrete Geometry are investigated, but referring to the more general setting of finite dimensional real Banach spaces (i.e., to Minkowski Geometry). In several cases such problems are investigated in the even more general context of spaces with so-called asymmetric norms (gauges). In many cases the extension of basic geometric notions, needed for posing these problems in non-Euclidean Banach spaces, is already interesting enough.
2016 Dec 05

Combinatorics: Klim Efremenko (TAU) " Testing Equality in Communication Graphs"

11:00am to 1:00pm

Location: 

B220 Rothberg (CS)
Speaker: Klim Efremenko (TAU) Title: Testing Equality in Communication Graphs Abstract: Let G=(V,E) be a connected undirected graph with k vertices. Suppose that on each vertex of the graph there is a player having an n-bit string. Each player is allowed to communicate with its neighbors according to a (static) agreed communication protocol and the players must decide, deterministically, if their inputs are all equal. What is the minimum possible total number of bits transmitted in a protocol solving this problem? We determine this minimum up to a lower order
2017 Jan 23

Combinatorics: Elchanan Mossel (MIT) "Lower Bounds on Same-Set Inner Product in Correlated Spaces"

11:00am to 1:00pm

Location: 

Rothberg B220 (CS bldg)
Speaker: Elchanan Mossel (MIT) Title: Lower Bounds on Same-Set Inner Product in Correlated Spaces Abstract: Suppose we pick X uniformly from {0,1,2}^n and Y is picked by letting each Y(i) = X(i) or X(i) + 1 mod 3 with probability 0.5 each independently. Is it true that for every set S with |S| > c 2^n it holds that the probability that both X and Y are in S is at least g(c) > 0, where g does not depend on the dimension n? Similar questions were asked before in different contexts. For example,

Pages