2016
Mar
29

# Events & Seminars

2015
Dec
17

# Groups & dynamics: Rene Rühr, Distribution of Shapes of Orthogonal Lattices

10:00am to 11:30am

## 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

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

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

2017
Dec
12

# T&G: Yoel Groman (Columbia), Generation of the Fukaya category of a Lagrangian torus fibration by a section

1:00pm to 2:30pm

## Location:

Room 70A, Ross Building, Jerusalem, Israel

The (wrapped) Fukaya category of a symplectic manifold is a category whose objects are Lagrangian submanifolds and which contains a wealth of information about the symplectic topology. I will discuss the construction of the wrapped Fukaya category for certain completely integrable Hamiltonian systems. These are 2n-dimensional symplectic manifolds carrying a system of n commuting Hamiltonians surjecting onto Euclidean space. This gives rise to a Lagrangian torus fibration with singularities.

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

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

2016
Nov
03

# Groups and dynamics - Misha Belolipetsky

10:30am to 11:30am

## Location:

Ross 70

Speaker: Misha Belolipetsky

Title: Arithmetic Kleinian groups generated by elements of finite order

Abstract:

We show that up to commensurability there are only finitely many

cocompact arithmetic Kleinian groups generated by rotations. The proof

is based on a generalised Gromov-Guth inequality and bounds for the

hyperbolic and tube volumes of the quotient orbifolds. To estimate the

hyperbolic volume we take advantage of known results towards Lehmer's

problem. The tube volume estimate requires study of triangulations of

Title: Arithmetic Kleinian groups generated by elements of finite order

Abstract:

We show that up to commensurability there are only finitely many

cocompact arithmetic Kleinian groups generated by rotations. The proof

is based on a generalised Gromov-Guth inequality and bounds for the

hyperbolic and tube volumes of the quotient orbifolds. To estimate the

hyperbolic volume we take advantage of known results towards Lehmer's

problem. The tube volume estimate requires study of triangulations of

2016
Mar
15

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.

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
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.

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 1:00pm11:00am 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

$\binom{t-1}{r} \leq m \leq \binom{t}{r}- \gamma_r t^{r-2}$

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

$\binom{t-1}{r} \leq m \leq \binom{t}{r}- \gamma_r t^{r-2}$

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.

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.

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

$$|\chi(g)| = O(\chi(1)^\alpha),$$

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

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

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)