2016 Jun 02

# Groups & dynamics: Todor Tsankov (Paris-Diderot): On metrizable universal minimal flows

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 Mar 29

# Dynamics lunch seminar: Brandon Seward (HUJI): Entropy theory for non-amenable groups (part IV)

12:00pm to 1:45pm

Ross 70
2017 May 18

# Basic notions: Ehud de Shalit - The Loxton - van der Poorten conjecture

4:00pm to 5:00pm

Abstract: Adamczewski and Bell proved in the 2013 the Loxton - van der Poorten conjecture. It says the following. Let f be a Laurent power series (with complex coefficients) and let \sigma_p be the operator substituting x^p for x in f. Suppose that f satisfies a homogenous polynomial equation in the operator \sigma_p with coefficients which are rational functions, and a similar equation in the operator \sigma_q where p and q are multiplicatively independent natural numbers. Then f is a rational function.
2017 May 25

# Basic notions: Ehud de Shalit - The Loxton - van der Poorten conjecture

4:00pm to 5:00pm

Abstract: Adamczewski and Bell proved in the 2013 the Loxton - van der Poorten conjecture. It says the following. Let f be a Laurent power series (with complex coefficients) and let \sigma_p be the operator substituting x^p for x in f. Suppose that f satisfies a homogenous polynomial equation in the operator \sigma_p with coefficients which are rational functions, and a similar equation in the operator \sigma_q where p and q are multiplicatively independent natural numbers. Then f is a rational function.
2017 Apr 30

# Combinatorics: Amir Yehudayoff (Technion) TBA

Repeats every week every Sunday until Sun Jun 25 2017 except Sun Apr 30 2017.
11:00am to 1:00pm

11:00am to 1:00pm
11:00am to 1:00pm
11:00am to 1:00pm
11:00am to 1:00pm
11:00am to 1:00pm
11:00am to 1:00pm
11:00am to 1:00pm
11:00am to 1:00pm

## Location:

Rothberg B221 (CS building)
Speaker: Misha Tyomkyn (TAU) Title: Lagrangians of hypergraphs and the Frankl-Furedi conjecture Abstract: Frankl and Furedi conjectured in 1989 that the maximum Lagrangian of all r-uniform hypergraphs of given size m is realised by the initial segment of the colexicographic order. For r=3 this was partially solved by Talbot, but for r\geq 4 the conjecture was widely open. We verify the conjecture for all r\geq 4, whenever $\binom{t-1}{r} \leq m \leq \binom{t}{r}- \gamma_r t^{r-2}$ for a constant $\gamma_r>0$. This range includes the principal case
2015 Dec 24

# Amitsur Algebra: Michael Larsen (Indiana U)

12:00pm to 1:15pm

## Location:

Manchester Building (room 209), Jerusalem, Israel
Title: Character values on compact simple Lie groups Abstract: This work is part of a joint project with Aner and others to find upper bounds for values of irreducible characters in two related settings: compact simple Lie groups and finite groups of Lie type. I will discuss the first case, presenting bounds of the form $$|\chi(g)| = O(\chi(1)^\alpha),$$
2015 Nov 19

# Amitsur Algebra: Avinoam Mann (HUJI), "Irreducible characters of some p-groups"

12:00pm to 1:15pm

## Location:

Manchester Building (room 209), Jerusalem, Israel
Abstract: We will discuss the characters of some classes of finite p-groups, in particular groups of maximal class and generalizations, and normally monomial groups.
2016 Jan 14

# Amitsur Algebra: Frauke Bleher (U of Iowa): Holomorphic differentials in positive characteristic

12:00pm to 1:15pm

## Location:

Manchester Building (room 209), Jerusalem, Israel
Title: Holomorphic differentials in positive characteristic Abstract: This talk is about joint work with Ted Chinburg and Aristides Kontogeorgis. Let X be a smooth projective curve over an algebraically closed field k of positive characteristic p. Suppose G is a finite group with non-trivial
2015 Dec 03

# Amitsur Algebra: Boris Plotkin (Hebrew U)

12:00pm to 1:15pm

## Location:

Manchester Building (room 209), Jerusalem, Israel
Title: Algebraic Geometry in an arbitrary variety of algebras and Algebraic Logic Abstract: I will speak about a system of notions which lead to interesting new problems for groups and algebras as well as to reinterpretation of some old ones.
2016 Mar 29

# Dynamics & probability: Paul Nelson (ETH) - Microlocal lifts and quantum unique ergodicity on GL(2,Q_p)

2:00pm to 3:00pm

## Location:

Manchester building, Hebrew University of Jerusalem, (Room 209)
Abstract: There are by now several celebrated measure classification results to the effect that a measure is uniform provided it possesses sufficient "invariance" as quantified by stabilizer, entropy, or recurrence. In some applications, part of the challenge is to identify or construct measures to which these hypotheses apply.
2016 Mar 08

# Dynamics & probability: Elon Lindenstrauss (Mean dimension and embedding of Z^d actions)

2:00pm to 3:00pm

## Location:

Manchester building, Hebrew University of Jerusalem, (Room 209)
2018 Jan 15

# Michael Farber: "Robot motion planning and equivariant Bredon cohomology"

9:00am to 11:00am

## Location:

IIAS, Feldman Building, Givat Ram

Abstract: The motion planning problem of robotics leads to an interesting invariant of topological spaces, TC(X), depending on the homotopy type of X = the configuration space of the system. TC(X) is an integer reflecting the complexity of motion planning algorithms for all systems (robots) having X as their configuration space. Methods of algebraic topology allow to compute or to estimate TC(X) in many examples of practical interest. In the case when the space X is aspherical the number TC(X) depends only on the fundamental group of X.

2018 Jan 22

# HD-Combinatorics: Frank Calegari, "Methods for computing homology and cohomology"

9:00am to 11:00am

## Location:

IIAS, Feldman Building, Givat Ram
2018 Mar 12

# HD-Combinatorics Special Day: Cohomology on Sheafs for graphs and complexes (organised by Uriya First)

10:00am to 5:00pm

## Location:

IIAS, Feldman Building, Givat Ram
2018 Mar 05

# HD-Combinatorics Special Day: Samplers in Computer Science (organised by Amnon Ta-Shma)

10:00am to 5:00pm

## Location:

IIAS, Feldman Building, Givat Ram