2016 Apr 21

# Amitsur Algebra: Konstantin Golubev (HU)

12:00pm to 1:15pm

## Location:

Manchester Building (room 209), Jerusalem, Israel
Title: Spectral approach to the chromatic number of a simplicial complex
Abstract: In this talk, we'll summarize results obtained in recent years in a pursuit for spectral bounds for the chromatic number of a simplicial complex. As the principal application, we'll show that Ramanujan complexes serve as family of explicitly constructed complexes with large girth and large chromatic number. We'll also present other results, such as a bound on the expansion and a bound on the mixing of a complex, and refer to open questions.
2018 Jun 14

# Colloquium - Zuchovitzky lecture: Lior Yanovski (HUJI) "Homotopy cardinality and the l-adic analyticity of Morava-Euler characteristic"

2:30pm to 3:30pm

## Location:

Manchester Building (Hall 2), Hebrew University Jerusalem
A finite set has an interesting numerical invariant - its cardinality. There are two natural generalizations of "cardinality" to a (homotopy) invariant for (suitably finite) spaces. One is the classical Euler characteristic. The other is the Baez-Dolan "homotopy cardinality". These two invariants, both natural from a certain perspective, seem to be very different from each other yet mysteriously connected. The question of the precise relation between them was popularized by John Baez as one of the "mysteries of counting".
2016 Jan 07

# Amitsur Algebra: Gili Schul (Hebrew U): Rapid expansion in finite simple groups

12:00pm to 1:15pm

## Location:

Manchester Building (room 209), Jerusalem, Israel
Title: Rapid expansion in finite simple groups
Abstract: We show that small normal subsets $A$ of finite simple groups expand
very rapidly -- namely, $|A^2| \ge |A|^{2-\epsilon}$, where $\epsilon >0$ is
arbitrarily small.
Joint work with M. W. Liebeck and A. Shalev
2018 Jan 25

# Special seminar: Sylvian Cappell (NYU) "What can be the fixed point sets of a given finite group acting on a non-simply-connected compact space?"

10:30am to 11:30am

## Location:

Ross 70
We will report on a joint work with Shmuel Weinberger of U. of Chicago & Min Yan of Hong Kong U. of Sci. & Tech.
2018 Apr 22

# Geometric, Topological and Computational Aspects of High-Dimensional Combinatorics

Sun, 22/04/2018 (All day) to Thu, 26/04/2018 (All day)

## Location:

Israel Institute for Advanced Studies, The Hebrew University of Jerusalem
2018 Feb 13

# 2-Day Meeting on Infinite Ergodic Theory & Related Fields

Tue, 13/02/2018 - 10:00 to Wed, 14/02/2018 - 17:00

## Location:

Hebrew University
2016 Jun 16

# Amitsur Algebra: Gili Golan, "The generation problem in Thompson group F"

12:00pm to 1:15pm

## Location:

Manchester Building (room 209), Jerusalem, Israel
We show that the generation problem in Thompson group F is decidable, i.e., there is an algorithm which decides if a finite set of elements of F generates the whole F. The algorithm makes use of the Stallings 2-core of subgroups of F, which can be defined in an analogue way to the Stallings core of subgroups of a free group. An application of the algorithm shows that F is a cyclic extension of a group K which has a maximal elementary amenable subgroup B. The group B is a copy of a subgroup of F constructed by Brin.
2016 Apr 07

# Amitsur Algebra: Ayala Byron (HUJI), "Definable fields in the free group"

12:00pm to 1:15pm

## Location:

Manchester Building (room 209), Jerusalem, Israel
Abstract: In the early 2000s Sela proved that all non-abelian free groups share a common first-order theory. Together with R. Sklinos, we use tools developed in his work to show that no infinite field is definable in this theory. In this talk we will survey the line of proof for a formal solution theorem for a simple sort of definable sets, that have a structure of a hyperbolic tower, and use it to characterize definable sets that do not carry a definable structure of an abelian group.
2018 Apr 25

# Analysis Seminar: Latif Eliaz "The Essential Spectrum of Schroedinger Operators on Graphs"

12:00pm to 1:00pm

## Location:

Room 70, Ross Building

It is known that the essential spectrum of aSchrödinger operator H on\ell^2(\mathbb{N})  is equal to the union of the spectra of right limits ofH. The naturalgeneralization of this relation to \mathbb{Z}^n  is known to hold as well.In this talk we study thepossibility of generalizing this characterization of \sigma_{ess}(H)  tographs. We show that the general statement fails, while presenting natural families of models where it still holds.

2013 Dec 11

# Eshnav: Nati Linial - "Games on graphs, elusive properties and a bit of topology and algebra"

Nati Linial
6:00pm to 7:00pm

## Location:

Math 2 (Manchester building)
2014 Jan 01

# Eshnav: Dror Bar-Natan - "Knots in 4D and the simplest problem regarding them"

## Lecturer:

Prof. Dror Bar-Natan
6:00pm to 7:00pm

## Location:

Math 2 (Manchester building)
2014 Mar 05

# Eshnav: Ehud De-Shalit - "P-adic numbers: Really not real"

Ehud De-Shalit
6:00pm to 7:00pm

## Location:

Math 2 (Manchester building)
2014 May 07

# Eshnav: Benjamin Weiss - "The road coloring problem and symbolic dynamics"

Benjamin Weiss
6:00pm to 7:00pm

## Location:

Math 2 (Manchester building)
2014 Jun 11

# Eshnav: Ori Gurel-Gurevich - "Recurrent drunkards, transient birds and electric networks"

## Lecturer:

Ori Gurel-Gurevich
6:00pm to 7:00pm

## Location:

Math 2 (Manchester building)
2014 Mar 19

# Eshnav: Itay Kaplan - "How to solve algebraic problems usings mathematical logic"

Itay Kaplan
6:00pm to 7:00pm

## Location:

Math 2 (Manchester building)