2016
Jun
08

# Events & Seminars

2016
Jan
06

# Topology & geometry, Egor Shelukhin (IAS), "The L^p diameter of the group of area-preserving diffeomorphisms of S^2"

11:00am to 12:45pm

## Location:

Ross building, Hebrew University (Seminar Room 70A)

Abstract: We use a geometric idea to give an analytic estimate for the word-length in the pure braid group of S^2. This yields that the L^1-norm (and hence each L^p-norm, including L^2) on the group of area-preserving diffeomorphisms of S^2 is unbounded. This solves an open question arising from the work of Shnirelman and Eliashberg-Ratiu. Joint work in progress with Michael Brandenbursky.

2016
Feb
24

# Topology & geometry, Mikhail Katz (Bar Ilan University), "Determinantal variety and bi-Lipschitz equivalence"

11:00am to 12:45pm

## Location:

Ross building, Hebrew University (Seminar Room 70A)

Abstract: The unit circle viewed as a Riemannian manifold has diameter (not 2 but rather) π, illustrating the difference between intrinsic and ambient distance. Gromov proceeded to erase the difference by pointing out that when a Riemannian manifold is embedded in L∞, the intrinsic and the ambient distances coincide in a way that is as counterintuitive as it is fruitful. Witness the results of his 1983 Filling paper.

2015
Dec
02

# Topology & geometry: Pavel Paták (HUJI), "Homological non-embeddability and a qualitative topological Helly-type theorem"

11:00am to 12:45pm

## Location:

Ross building, Hebrew University (Seminar Room 70A)

Abstract: The classical theorem of Van Kampen and Flores states that the k-dimensional skeleton of (2k+2)-dimensional simplex cannot be embedded into R2k.
We present a version of this theorem for chain maps and as an application we prove a qualitative topological Helly-type theorem.
If we define the Helly number of a finite family of sets to be one if all sets in the family have a point in common and as the largest size of inclusion-minimal subfamily with empty intersection otherwise, the theorem can be stated as follows:

2016
Apr
06

# Topology & geometry, Sari Ghanem (Université Joseph Fourier - Grenoble I ), "The decay of SU(2) Yang-Mills fields on the Schwarzschild black hole with spherically symmetric small energy initial data"

11:00am to 12:45pm

## Location:

Levi building, Hebrew University ( Room 06)

**Note the special location**
Abstract:

2016
Feb
17

# Menachem Magidor 70th Birthday Conference

Wed, 17/02/2016 (All day) to Fri, 19/02/2016 (All day)

2016
Mar
31

# Groups & dynamics: Paul Nelson (ETH) - Quantum variance on quaternion algebras

10:00am to 11:00am

## Location:

Ross building, Hebrew University of Jerusalem, (Room 70)

To every topological group, one can associate a unique universal
minimal flow (UMF): a flow that maps onto every minimal flow of the
group. For some groups (for example, the locally compact ones), this
flow is not metrizable and does not admit a concrete description.
However, for many "large" Polish groups, the UMF is metrizable, can be
computed, and carries interesting combinatorial information. The talk
will concentrate on some new results that give a characterization of
metrizable UMFs of Polish groups. It is based on two papers, one joint

2016
Dec
01

# Groups and dynamics: Masaki Tsukamoto (lecture 1)

10:30am to 11:30am

## Location:

Ross 70

INTRODUCTION TO MEAN DIMENSION AND THE EMBEDDING PROBLEM OF DYNAMICAL SYSTEMS (Part 1)

2016
Nov
24

# Groups and dynamics- Oren Becker

10:30am to 11:30am

## Location:

Ross 70

Speaker: Oren Becker
Title: Locally testable groups
Abstract:
Arzhantseva and Paunescu [AP2015] showed that if two permutations X and Y in Sym(n) nearly commute (i.e. XY is close to YX), then the pair (X,Y) is close to a pair of permutations that really commute.

2016
Dec
22

2016
Jan
07

# Groups & dynamics: Mark Shusterman (TAU) - Ranks of subgroups in boundedly generated groups

10:00am to 11:00am

## Location:

Ross building, Hebrew University of Jerusalem, (Room 70)

To every topological group, one can associate a unique universal
minimal flow (UMF): a flow that maps onto every minimal flow of the
group. For some groups (for example, the locally compact ones), this
flow is not metrizable and does not admit a concrete description.
However, for many "large" Polish groups, the UMF is metrizable, can be
computed, and carries interesting combinatorial information. The talk
will concentrate on some new results that give a characterization of
metrizable UMFs of Polish groups. It is based on two papers, one joint

2016
Dec
08

2016
Dec
29

2016
Mar
03

# Groups & dynamics: Karim Adiprasito (HUJI) - Contractible manifolds, hyperbolicity and the fundamental pro-group at infinity

10:00am to 11:00am

## Location:

Ross building, Hebrew University of Jerusalem, (Room 70)

To every topological group, one can associate a unique universal
minimal flow (UMF): a flow that maps onto every minimal flow of the
group. For some groups (for example, the locally compact ones), this
flow is not metrizable and does not admit a concrete description.
However, for many "large" Polish groups, the UMF is metrizable, can be
computed, and carries interesting combinatorial information. The talk
will concentrate on some new results that give a characterization of
metrizable UMFs of Polish groups. It is based on two papers, one joint

2016
Nov
17

# Groups and dynamics: Arie Levit

10:30am to 11:30am

## Location:

Ross 70

Speaker: Arie Levit
Weizmann Institute
Title: Local rigidity of uniform lattices
Abstract: A lattice is topologically locally rigid (t.l.r) if small deformations of it are isomorphic lattices. Uniform lattices in Lie groups were shown to be t.l.r by Weil [60']. We show that uniform lattices are t.l.r in any compactly generated topological group.