2018 May 02

# Analysis Seminar: Bo'az Klartag "Convex geometry and waist inequalities"

12:00pm to 1:00pm

## Location:

room 70, Ross Building
Abstract: We will discuss connections between Gromov's work on isoperimetry of waists and Milman's work on the M-ellipsoid of a convex body. It is proven that any convex body K in an n-dimensional Euclidean space has a linear image K_1 of volume one satisfying the following waist inequality: Any continuous map f from K_1 to R^d has a fiber f^{-1}(t) whose (n-d)-dimensional volume is at least c^{n-d}, where c > 0 is a universal constant. Already in the case where f is linear, this constitutes a slight improvement over known results.
2018 Feb 05

# HD-Combinatorics special day: Stability and property testing (organized by Oren Becker)

(All day)

## Location:

Room 130, IIAS, Feldman Building, Givat Ram
2018 Feb 26

# HD-Combinatorics Special Day on On Random groups and property T (organized by Izhar Oppenheim)

(All day)

## Location:

Room 130, IIAS, Feldman Building, Givat Ram

10:00-11:00: Izhar Oppenheim, Introduction to Property (T)

11:30-12:30Izhar Oppenheim, Introduction to Random Groups

14:00-16:00Izhar Oppenheim, Property (T) and hyperbolicity for random groups in the permutation model
2018 Jan 31

# Analysis Seminar: Balazs Rath "Self-organized criticality in dynamic random graph models"

12:00pm to 1:00pm

2016 Jun 09

# Joint Amitsur Algebra&NT Seminar: Shai Haran (Technion), "New foundations for geometry"

12:00pm to 1:15pm

## Location:

Manchester Building (Ross 63), Jerusalem, Israel
*** Please note the LOCATION *** We shall give a simple generalization of commutative rings. The category GR of such generalized rings contains ordinary commutative rings (fully, faithfully), but also the "integers" and the "residue field" at a real or complex place of a number field ; the "field with one element" F1 (the initial object of GR) ; the "Arithmetical Surface" (the categorical sum of the integers Z with them self). We shall show this geometry sees the real and complex places of a number field K : the valuation sub GR of K correspond to the finite and
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. Based on joint work with S.Evra, A.Lubotzky and O.Parzanchevski.
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.
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.

2018 Jan 30

# Action Now Seminar: Weikun He (HUJI), "Discretized sum-product estimates in higher dimension"

2:30pm to 3:30pm

## Location:

IIAS, HUJI, Feldman Building, Room 130
2018 Jan 30

# Action Now Seminar: Oren Becker (HUJI), "Stability and Invariant Random Subgroups"

11:30am to 12:30pm

## Location:

IIAS, HUJI, Feldman Building, Room 130
2018 Jan 30

# Action Now Seminar: Menny Aka (ETH), "On rational planes in four-dimensional space and their associated lattices"

4:00pm to 5:00pm

## Location:

IIAS, HUJI, Feldman Building, Room 130
2018 Jan 30

# Action Now Seminar: Tammy Ziegler (HUJI), "Dynamics, arithmetic progressions and approximate cohomology"

10:00am to 11:00am

## Location:

IIAS, HUJI, Feldman Building, Room 130