# Seminars

Upcoming seminars can also be found here.
2018 Jun 28

# Basic Notions: Barry Simon "More Tales of our Forefathers (Part II)"

4:00pm to 5:30pm

## Location:

Manchester Hall 2
This is not a mathematics talk but it is a talk for mathematicians. Too often, we think of historical mathematicians as only names assigned to theorems. With vignettes and anecdotes, I'll convince you they were also human beings and that, as the Chinese say, "May you live in interesting times" really is a curse. Among the mathematicians with vignettes are Riemann, Newton, Poincare, von Neumann, Kato, Loewner, Krein and Noether.
2018 Jun 26

# Amitsur Symposium: Malka Schaps - "Symmetric Kashivara crystals of type A in low rank"

11:30am to 12:30pm

## Location:

Manchester House, Lecture Hall 2
The basis of elements of the highest weight representations of affine Lie algebra of type A can be labeled in three different ways, my multipartitions, by piecewise linear paths in the weight space, and by canonical basis elements. The entire infinite basis is recursively generated from the highest weight vector of operators f_i from the Chevalley basis of the affine Lie algebra, and organized into a crystal called a Kashiwara crystal. We describe cases where one can move between the different labelings in a non-recursive fashion, particularly when the crystal has some symmetry.
2018 Jun 27

# Amitsur Symposium: Tsachik Gelander - "Local rigidity of uniform lattices"

3:00pm to 4:00pm

## Location:

Manchester House, Lecture Hall 2
We establish topological local rigidity for uniform lattices in compactly generated groups, extending the result of Weil from the realm of Lie groups. We generalize the classical local rigidity theorem of Selberg, Calabi and Weil to irreducible uniform lattices in Isom(X) where X is a proper CAT(0) space with no Euclidian factors, not isometric to the hyperbolic plane. We deduce an analog of Wang’s finiteness theorem for certain non-positively curved metric spaces. This is a joint work with Arie Levit.
2018 Jun 27

# Amitsur Symposium: Amiram Braun - "The polynomial question in modular invariant theory, old and new"

11:30am to 12:30pm

## Location:

Manchester House, Lecture Hall 2
Let G be a finite group, V a finite dimensional G- module over a field F, and S(V) the symmetric algebra of V. The above problem seeks to determine when is the ring of invariants S(V)^G , a polynomial ring. In the non-modular case (i.e. char(F) being prime to order(G)), this was settled in the Shephard-Todd-Chevalley theorem. The modular case (i.e. char(F) divides order (G) ), is still wide open. I shall discuss some older results due to Serre, Nakajima , Kemper-Malle and explain some new results, mostly in dimension 3.
2018 Jun 26

# Amitsur Symposium: Lev Glebsky - "Approximations of groups by finite and linear groups"

4:30pm to 5:30pm

## Location:

Manchester House, Lecture Hall 2
The sofic groups and hyperlinear groups are groups approximable by finite symmetric and by unitary groups, respectively. I recall their definitions and discuss why those classes of groups are interesting. Then I consider approximations by other classes of groups and review some results, including rather recent ones by N. Nikolov, J. Schneider, A.Thom, https://arxiv.org/abs/1703.06092 . If time permits I'll speak about stability and its relations with approximability.
2018 Jun 26

# Amitsur Symposium: Arye Juhasz - "On the center of Artin groups"

2:00pm to 3:00pm

## Location:

Manchester House, Lecture Hall 2
Let A be an Artin group. It is known that if A is spherical (of finite type) and irreducible (not a direct sum), then it has infinite cyclic center. It is conjectured that all other irreducible Artin groups have trivial center. I prove this conjecture under a stronger assumption that not being spherical namely, if there is a standard generator which is not contained in any 3-generated spherical standard parabolic subgroup. The main tool is relative presentations of Artin groups.
2018 Jun 27

# Amitsur Symposium: Yael Algom-Kfir - "The metric completion of an asymmetric metric space"

4:30pm to 5:30pm

## Location:

Manchester House, Lecture Hall 2
The Teichmuller space with the Thurston metric and Outer Space with the Lipschitz metric are two examples of spaces with an asymmetric metric i.e. d(x,y) eq d(y,x). The latter case is also incomplete: There exist Cauchy sequences that do not have a limit. We develop the theory of the completion of an asymmetric space and give lots of examples. Time permitting we will describe the case of Outer Space.
2018 Jun 26

# Amitsur Symposium: Alex Lubotzky - "First order rigidity of high-rank arithmetic groups"

10:00am to 11:00am

## Location:

Manchester House, Lecture Hall 2
The family of high rank arithmetic groups is a class of groups playing an important role in various areas of mathematics. It includes SL(n,Z), for n>2 , SL(n, Z[1/p] ) for n>1, their finite index subgroups and many more. A number of remarkable results about them have been proven including; Mostow rigidity, Margulis Super rigidity and the Quasi-isometric rigidity.
2018 Jun 27

# Amitsur Symposium: Chloe Perin - "Forking independence in the free group"

2:00pm to 3:00pm

## Location:

Manchester House, Lecture Hall 2
Model theorists define, in structures whose first-order theory is "stable" (i.e. suitably nice), a notion of independence between elements. This notion coincides for example with linear independence when the structure considered is a vector space, and with algebraic independence when it is an algebraically closed field. Sela showed that the theory of the free group is stable. In a joint work with Rizos Sklinos, we give an interpretation of this model theoretic notion of independence in the free group using Grushko and JSJ decompositions.
2018 Jun 27

# Amitsur Symposium: Elyiahu Rips - "Free Engel groups" (joint work with Arye Juhasz)

10:00am to 11:00am

## Location:

Manchester House, Lecture Hall 2
A free n-Engel group is the relatively free group of the variety of groups with the identical relation [x, y, y,...,y (n times)]=1. Let n>=20. We show that the free Engel group on at least two generators is not locally nilpotent. Our approach to Engel groups combines
2018 Jun 26

# Amitsur Symposium: Aner Shalev - "The length and depth of finite groups, algebraic groups and Lie groups"

3:00pm to 4:00pm

## Location:

Manchester House, Lecture Hall 2
The length of a finite group G is defined to be the maximal length of an unrefinable chain of subgroups going from G to 1. This notion was studied by many authors since the 1940s. Recently there is growing interest also in the depth of G, which is the minimal length of such a chain. Moreover, similar notions were defined and studied for important families of infinite groups, such as connected algebraic groups and connected Lie groups.
2018 Jul 11

# Logic Seminar - Assaf Shani - "Borel equivalence relations and symmetric models"

11:00am to 1:00pm

## Location:

Ross 70A
We develop a correspondence between the study of Borel equivalence relations induced by closed subgroups of $S_\infty$, and the study of symmetric models of set theory without choice, and apply it to prove a conjecture of Hjorth-Kechris-Louveau (1998).
2018 Jun 25

# HD-Combinatorics Special Day: "Quantum ergodicity and spectral theory with a discrete flavour" (organized by Elon Lindenstrauss and Shimon Brooks)

(All day)

## Location:

Feldman Building, Givat Ram
Title for the day: "Quantum ergodicity and spectral theory with a discrete flavour"

9:00-10:50: Shimon Brooks (Bar Ilan), "Delocalization of Graph Eigenfunctions"
14:00-15:50: Elon Lindenstrauss (HUJI), "Quantum ergodicity on graphs and beyond"

See also the Basic Notions by Elon Lindenstrauss @ Ross 70 (16:30).

Abstract for morning session:
2018 Jun 25

# NT&AG: Gal Porat (HUJI), "Induction and Restriction of $(\varphi,\Gamma)$-Modules"

2:00pm to 3:00pm

## Location:

Room 70A, Ross Building, Jerusalem, Israel
Abstract. Let L be a non-archimedean local field of characteristic 0. In this talk we will present a variant of the theory of (\varphi,\Gamma)-modules associated with Lubin-Tate groups, developed by Kisin and Ren, in which we replace the Lubin-Tate tower by the maximal abelian extension \Gamma=Gal (L^ab/L). This variation allows us to compute the functors of induction and restriction for (\varphi,\Gamma)-modules, when the ground field L changes. If time permits, we will also discuss the Cherbonnier-Colmez theorem on overconvergence in our setting. Joint work with Ehud de Shalit.
2018 Jun 19

# T&G: Yaron Ostrover (Tel Aviv), Quantitative symplectic geometry in the classical phase space.

12:00pm to 1:30pm

## Location:

Room 110, Manchester Buildling, Jerusalem, Israel
We shall discuss several topics regarding symplectic measurements in the classical phase space. In particular: Viterbo's volume-capacity conjecture and its relation with Mahler conjecture, the symplectic size of random convex bodies, the EHZ capacity of convex polytopes (following the work of Pazit Haim-Kislev), and (if time permits) also computational complexity aspects of estimating symplectic capacities.