2016 Dec 22

# Amitsur Algebra: Mark Sapir (Vanderbilt)

12:00pm to 1:00pm

## Location:

Manchester Building, Room 209
Title: On groups with quadratic Dehn functions Abstract: This is a joint work with A. Olshanskii. We construct a finitely presented group with quadratic Dehn function and undecidable conjugacy problem.
2017 Mar 23

# Amitsur Algebra: Daniel Palacin, "Pseudo-finite groups containing an involution with a finite centralizer"

12:00pm to 1:00pm

## Location:

Manchester 209
Title: Pseudo-finite groups containing an involution with a finite centralizer.
2017 Jan 26

# Amitsur Algebra: Lev Glebsky, "Approximations of groups and equations over groups"

12:00pm to 1:00pm

## Location:

Manchester Building, Room 209
Title: Approximations of groups and equations over groups. Abstract: The talk is largely based on the paper which may be found here: https://authors.elsevier.com/a/1UN3b4~FOr6ze Abstract: Let G be a group and K a class of groups. I define a notion of approximation of G by K and give several characterizations of approximable by K groups. For example, the sofic groups, defined by B. Weiss, are the groups approximable by symmetric (or alternating) groups. In the case of sofic groups we have that the following are equivalent:
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
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.
2015 Nov 19

# Groups & dynamics: Lei Yang (HUJI) "Equidistribution of expanding translates of curves in homogeneous spaces and Diophantine approximation"

10:00am to 11:00am

## Location:

Ross 70
Title: Equidistribution of expanding translates of curves in homogeneous spaces and Diophantine approximation. Abstract: We consider an analytic curve $\varphi: I \rightarrow \mathbb{M}(n\times m, \mathbb{R}) \hookrightarrow \mathrm{SL}(n+m, \mathbb{R})$ and embed it into some homogeneous space $G/\Gamma$, and translate it via some diagonal flow
2015 Nov 12

# Groups & dynamics: Elon Lindenstrauss (HUJI), "Rigidity of higher rank diagonalizable actions in positive characteristic"

10:00am to 11:00am

## Location:

Ross 70
Title: Rigidity of higher rank diagonalizable actions in positive characteristic
2015 Dec 29

# Dynamics lunch: Tom Gilat (HUJI): "Measure rigidity for `dense' multiplicative semigroups (following Einsiedler and Fish)"

12:00pm to 1:00pm

## Location:

Manchester building, Hebrew University of Jerusalem, (Coffee lounge)
2015 Nov 24

# Dynamics & probability: Yaar Salomon (Stonybrook) "The Danzer problem and a solution to a related problem of Gowers"

2:00pm to 3:00pm

## Location:

Manchester building, Hebrew University of Jerusalem, (Room 209)
The Danzer problem and a solution to a related problem of Gowers Is there a point set Y in R^d, and C>0, such that every convex set of volume 1 contains at least one point of Y and at most C? This discrete geometry problem was posed by Gowers in 2000, and it is a special case of an open problem posed by Danzer in 1965. I will present two proofs that answers Gowers' question with a NO. The first approach is dynamical; we introduce a dynamical system and classify its minimal subsystems. This classification in particular yields the negative answer to Gowers'