2017 Jan 16

# Combinatorics: Yinon Spinka (TAU) "Long-range order in random colorings and random graph homomorphisms in high dimensions"

11:00am to 1:00pm

## Location:

Rothberg B220 (CS bldg)
Speaker: Yinon Spinka (TAU)
Title: Long-range order in random colorings and random graph homomorphisms in high dimensions
Abstract:
2017 Nov 27

# Combinatorics Seminar: Maria Hempel

11:00am to 12:30pm

## Location:

Room 130 at the IIAS
Title: Labeling and Eliminating Geometric Realization Spaces
Abstract: I will introduce a Moduli-space of Shapes of Polyhedra, and show how they may be eliminated by labeling their underlying combinatorial data. I discuss how this relates to geometric realization problems and in particular to flexibility of polyhedra.
2017 Apr 23

# Combinatorics: Amitay Kamber (HU) " Lp Expander Complexes"

11:00am to 1:00pm

## Location:

Rothberg B221 (CS building)
Speaker: Amitay Kamber, HU
Title: Lp Expander Complexes.
Abstract: In recent years, several different notions of high dimensional expanders have been proposed (which in general are not equivalent), each with its own goal and motivation. The goal of this talk is to propose another generalization, based on ideas from the representation theory of p-adic groups.
By comparing a complex to its universal cover, we show how to define Lp-expanders and in particular L2-expanders, which are Ramanujan complexes, generalizing the notions of expander graphs and Ramanujan graphs.
2016 Nov 14

# Combinatorics: Andrew Thomason (Cambridge) "Hypergraph containers"

11:00am to 1:00pm

## Location:

Rothberg (CS) B220
Speaker: Andrew Thomason, Cambridge
Title: Hypergraph containers
Abstract:
A collection of containers for a (uniform) hypergraph is a collection of
subsets of the vertex set such that every independent set lies inside a
container. It has been discovered (Balogh, Morris, Samotij, and Saxton)
that it is always possible to find such a collection for which the
containers are not big (close to independent) and the size of the
collection itself is quite small. This basic, if surprising, fact has many
2017 Oct 23

# Combinatorics seminar: Quang Nhat Le

11:00am to 12:30pm

## Location:

Eilat Hall at the IIAS
Title: Counting lattice points inside a d-dimensional polytope via Fourier analysis
Abstract: Given a convex body $B$ which is embedded in a Euclidean space $R^d$, we can ask how many lattice points are contained inside $B$, i.e. the number of points in the intersection of $B$ and the integer lattice $Z^d$. Alternatively, we can count the lattice points inside B with weights, which sometimes creates more nicely behaved lattice-point enumerating functions.
2016 Dec 26

# Combinatorics: Adam Sheffer (CalTech) "Geometric Incidences and the Polynomial Method"

10:00am to 11:45am

## Location:

B220 Rothberg (CS)
Title: Geometric Incidences and the Polynomial Method
Abstract: While the topic of geometric incidences has existed for several decades, in recent years it has been experiencing a renaissance due to the introduction of new polynomial methods. This progress involves a variety of new results and techniques, and also interactions with fields such as algebraic geometry and harmonic analysis.
2017 Jan 19

# Amitsur Algebra: Yiftach Barnea, "Old and New Results on Subgroup Growth in Pro-p Groups."

12:00pm to 1:00pm

## Location:

Manchester Building, Room 209
Title: Old and New Results on Subgroup Growth in Pro-p Groups.
Abstract: I will survey our current knowledge about subgroup growth in pro-p growth. In particular I will present new solutions to long standing open problems in the area:
1. What is the minimal subgroup growth of non-$p$-adic analytic pro-$p$ groups? (Joint work with Benjamin Klopsch and Jan-Christoph Schlage-Puchta.)
2. What are the subgroup growths of the Grigorchuk group and the Gupta-Sidki groups? (Joint work with Jan-Christoph Schlage-Puchta.)
2017 Jun 22

# Amitsur Algebra: Jan Dobrowolski

12:00pm to 1:00pm

## Location:

Manchester 209
Title: Inp-minimal ordered groups.
Abstract. The main goal of the talk is to present the proof of the theorem stating that inp-minimal (left)-ordered groups are abelian. This generalizes a previous result of P. Simon for bi-ordered inp-minimal groups.
2016 Dec 29

# Amitsur Algebra: Igor Rivin, "Random integer matrices"

12:00pm to 1:00pm

## Location:

Manchester Building, Room 209
Title: Random integer matrices
Abstract: I will discuss various models of random integer matrices, and their (occasionally surprising) properties. Some of the work discussed is joint with E. Fuchs.
2017 May 04

# Amitsur Algebra: Jasbir Chahal, " A tale of three elliptic curves"

12:00pm to 1:00pm

## Location:

Manchester 209
Title: A tale of three elliptic curves.
Abstract: We will show how the arithmetic of three elliptic curves answers three old questions in the Euclidean geometry.
2016 Dec 08

# Amitsur Algebra: George Glauberman (Chicago)

12:00pm to 1:15pm

## Location:

Manchester Building, Room 209
Title: Fixed points of finite groups on modules
Abstract: Suppose G is a finite group, p is a prime, S is a Sylow p-subgroup of G, and V is a G-module over a field of characteristic p. In some situations, an easy calculation shows that the fixed points of G on V are the same as the fixed points of the normalizer
of S in G. Generalizations of this result have been obtained previously to study the structure of G for p odd. We plan to describe a new generalization for p = 2. (This is part of joint work with J. Lynd that removes the classification of finite simple groups
2017 Mar 02

# Amitsur Algebra: Lev Glebsky, " Almost Congruence Extension Property for subgroups of free groups"

12:00pm to 1:00pm

## Location:

Manchester Building, Room 209
Title: Almost Congruence Extension Property for subgroups of free groups.
Abstract.
The talk essentially based on: https://arxiv.org/abs/1606.02345
Let G be a group and H every normal subgroup N of H is an intersection of some normal subgroup of G with H. The CEP appears in group theory in different context.
The following question seems to be very difficult:
Which finitely generated subgroup of a free group has CEP?
2017 Feb 09

# Amitsur Algebra: Evan DeCorte, "The spectral method for geometric colouring problems"

12:00pm to 1:00pm

## Location:

Manchester Building, Room 209
Title: The spectral method for geometric colouring problems
2017 Jun 29

12:00pm to 1:00pm

## Location:

Manchester 209
Title: Stability patterns in representation theory and applications
Abstract:
Many natural sequences of objects come equipped with group actions, e.g. the symmetric group on n letters acting on a space X_n. This leads to fundamental instability of invariants, such as homology, arising from the representation theory of the sequence of groups. Representation stability is a new and increasingly important set of ideas that describe a sense in which such sequence of representations (of different groups) stabilizes.
2017 Jan 12

# Amitsur Algebra: Uriya First, "Semisimply degenerate quadratic forms and a conjecture of Grothendieck and Serre"

12:00pm to 1:00pm

## Location:

Manchester Building, Room 209
Title: Semisimply degenerate quadratic forms and a conjecture of Grothendieck and Serre
(joint work with E. Bayer-Fluckiger)
Abstract: