2017
Jan
05

# Events & Seminars

2017
Nov
28

# T&G: Benjamin Ackermann (Hebrew University), Kodaira's embedding theorem

12:00pm to 1:30pm

## Location:

Room 70A, Ross Building, Jerusalem, Israel

In this talk we present a proof of the Kodaira's theorem that gives a sufficient condition on the existence of an embedding of a Kahler manifold into CPn. This proof is based on the Kodaira Vanishing theorem, using a sheaf-cohomological translation of the embedding conditions.

לאירוע הזה יש שיחת וידאו.

הצטרף: https://meet.google.com/mcs-bwxr-iza

לאירוע הזה יש שיחת וידאו.

הצטרף: https://meet.google.com/mcs-bwxr-iza

2015
Dec
07

# Number theory: Jean-Baptiste Teyssier (HUJI) "Kedlaya-Mochizuki theorem and applications"

4:00pm to 5:15pm

## Location:

Ross Building, room 70A

Let X be a complex manifold and let M be a meromorphic connection on X with

poles along a normal crossing divisor D. Levelt-Turrittin theorem asserts that the pull-back of M to the formal neighbourhood of a codimension 1 point in D decom poses (after ramification) into elementary factors easy to work with.

This decomposition may not hold at some other points of D. When it does, we say

that M has good formal decomposition along D. A conjecture of Sabbah, recently

proved by Kedlaya and Mochizuki independently, asserts roughly the

poles along a normal crossing divisor D. Levelt-Turrittin theorem asserts that the pull-back of M to the formal neighbourhood of a codimension 1 point in D decom poses (after ramification) into elementary factors easy to work with.

This decomposition may not hold at some other points of D. When it does, we say

that M has good formal decomposition along D. A conjecture of Sabbah, recently

proved by Kedlaya and Mochizuki independently, asserts roughly the

2015
Nov
09

# Number theory: Ishai Dan-Cohen (Essen), "Towards Chabauty-Kim loci for the polylogarithmic quotient over an arbitrary number field"

4:00pm to 5:45pm

## Location:

Ross Building, room 70, Jerusalem, Israel

Title: Towards Chabauty-Kim loci for the polylogarithmic quotient over an arbitrary number field

Abstract: Let K be a number field and let S be an open

subscheme of Spec O_K.

Minhyong Kim has developed a method for

bounding the set of S-valued points on a

hyperbolic curve X over S; his method opens

a new avenue in the quest for an "effective

Mordell conjecture".

But although Kim's approach has lead to the

construction of explicit bounds in special

cases, the problem of realizing the potential

Abstract: Let K be a number field and let S be an open

subscheme of Spec O_K.

Minhyong Kim has developed a method for

bounding the set of S-valued points on a

hyperbolic curve X over S; his method opens

a new avenue in the quest for an "effective

Mordell conjecture".

But although Kim's approach has lead to the

construction of explicit bounds in special

cases, the problem of realizing the potential

2017
Dec
19

# T&G: Yakov Eliashberg (Stanford), Simplifying singularities of Lagrangian skeleta

1:00pm to 2:30pm

## Location:

Room 63, Ross Building, Jerusalem, Israel

I will discuss in the talk David Nadler’s “arborealizaton conjecture” and will sketch its proof. The conjecture states that singularities of a Lagrangian skeleton of a symplectic Weinstein manifold could be always simplified to a finite list of singularities, called ``arboreal”. This is a joint work with Daniel Albarez-Gavela, David Nadler and Laura Starkston.

2016
Mar
15

2015
Dec
17

# Groups & dynamics: Robert Hough (IAS) - Mixing and cut-off on cyclic groups

12:00pm to 1:00pm

## Location:

Einstein 110

Consider a sequence of random walks on $\mathbb{Z}/p\mathbb{Z}$ with symmetric generating sets $A= A(p)$. I will describe known and new results regarding the mixing time and cut-off. For instance, if the sequence $|A(p)|$ is bounded then the cut-off phenomenon does not occur, and more precisely I give a lower bound on the size of the cut-off window in terms of $|A(p)|$. A natural conjecture from random walk on a graph is that the total variation mixing time is bounded by maximum degree times diameter squared.

2015
Nov
05

# Groups & Dynamics : Ilya Khayutin (HUJI)

9:45am to 11:00am

## Location:

Manchester building, Hebrew University of Jerusalem, (Room 209)

Title: Arithmetic of Double Torus Quotients and the Distribution of Periodic Torus Orbits

Abstract:

In this talk I will describe some new arithmetic invariants for pairs of torus orbits on inner forms of PGLn and SLn. These invariants allow us to significantly strengthen results towards the equidistribution of packets of periodic torus orbits on higher rank S-arithmetic quotients. An important aspect of our method is that it applies to packets of periodic orbits of maximal tori which are only partially split.

Abstract:

In this talk I will describe some new arithmetic invariants for pairs of torus orbits on inner forms of PGLn and SLn. These invariants allow us to significantly strengthen results towards the equidistribution of packets of periodic torus orbits on higher rank S-arithmetic quotients. An important aspect of our method is that it applies to packets of periodic orbits of maximal tori which are only partially split.

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

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

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