2019
Nov
03

# Eventss

2019
Nov
07

# Groups & Dynamics seminar: Alex Margolis (Technion) “Almost normal subgroups and quotient spaces״

10:00am to 11:00am

## Location:

Ross 70

Abstract: A subgroup is said to be almost normal if it is commensurable

to all of its conjugates. Even though there may not be a well-defined

quotient group, there is still a well-defined quotient space that admits

an isometric action by the ambient group. We can deduce many geometric

and algebraic properties of the ambient group by examining this action.

In particular, we will use quotient spaces to prove a relative version

of Stallings-Swan theorem on groups of cohomological dimension one. We

to all of its conjugates. Even though there may not be a well-defined

quotient group, there is still a well-defined quotient space that admits

an isometric action by the ambient group. We can deduce many geometric

and algebraic properties of the ambient group by examining this action.

In particular, we will use quotient spaces to prove a relative version

of Stallings-Swan theorem on groups of cohomological dimension one. We

2019
Nov
25

# Combinatorics: Itamar Vigdorovich (Weizmann)

10:00am to 12:00pm

## Location:

C-400, CS building

**Speaker:**Itamar Vigdorovich (Weizmann)

**Title:**Complexes, Lie groups, lattices and quantum homological codes

**Abstract:**

2019
Nov
11

# Combinatorics: Barak Weiss (TAU)

10:00am to 12:00pm

## Location:

C-400, CS building

**Speaker: **Barak Weiss (TAU)

**Title**: New bounds on the covering radius of a lattice.

**Abstract:**

We obtain new upper bounds on the minimal density of lattice coverings of R^n by dilates of a convex body K. We also obtain bounds on the probability (with respect to the natural Haar-Siegel measure on the space of lattices) that a randomly chosen lattice L satisfies L + K = R^n. As a step in the proof, we utilize and strengthen results on the discrete Kakeya problem. This is joint work with Or Ordentlich and Oded Regev.

2019
Nov
18

# Combinatorics: Ofir Gorodetsky (TAU)

10:00am to 12:00pm

## Location:

C-400, CS building

**Speaker:**Ofir Gorodetsky (TAU)

**Title:**The Anatomy of Integers and Ewens Permutations

**Abstract:**

2019
Nov
26

2019
Nov
05

2020
Jan
28

# Uri Bader (Weizmann)

12:00pm to 1:00pm

2019
Oct
28

# Combinatorics: Zlil Sela (HUJI) "Combinatorics and geometry in non-commutative algebraic geometry"

10:00am to 12:00pm

## Location:

CS building, room C-221

Speaker: Zlil Sela, HUJI

Title: Combinatorics and geometry in non-commutative algebraic geometry

Abstract:

Title: Combinatorics and geometry in non-commutative algebraic geometry

Abstract:

2020
Apr
30

2019
Oct
31

# Groups & Dynamics seminar - Vincent Guirardel (Universite de Rennes 1) "Measure Equivalence rigidity for Out(Fn)"

10:00am to 11:00am

## Location:

Ross 70

Abstract:

Measure equivalence of countable groups is a measure theoretic analogue

of quasi-isometry.

For example, any two lattices in the same Lie group are by definition

measure equivalent.

We prove that any countable group that is measure equivalent to Out(Fn)

is virtually isomorphic to Out(Fn). This is a joint work with Camille

Horbez.

Measure equivalence of countable groups is a measure theoretic analogue

of quasi-isometry.

For example, any two lattices in the same Lie group are by definition

measure equivalent.

We prove that any countable group that is measure equivalent to Out(Fn)

is virtually isomorphic to Out(Fn). This is a joint work with Camille

Horbez.

2019
Oct
29

# Zemer Kosloff, Finitary isomorphisms of Brownian motions

2:00pm to 3:00pm

Ornstein and Shields (Advances in Math., 10:143-146, 1973) proved that Brownian motion reflected on a bounded region is an infinite entropy Bernoulli flow and thus Ornstein theory yielded the existence of a measure-preserving isomorphism between any two such Brownian motions. For fixed h >0, we construct by elementary methods, isomorphisms with almost surely finite coding windows between Brownian motions reflected on the intervals [0, qh] for all positive rationals q. This is joint work with Terry Soo.

2019
Nov
19

# Tom Meyerovitch (BGU), Efficient finitary codings by Bernoulli processes

2:00pm to 3:00pm

Abstract:

Recently Uri Gabor refuted an old conjecture stating that any

finitary factor of an i.i.d process is finitarly isomorphic to an

i.i.d process. Complementing Gabor's result,

in this talk, which is based on work in progress with Yinon Spinka,

we will prove that any countable-valued process which is admits a

finitary a coding by some i.i.d process furthermore admits an

$\epsilon$-efficient finitary coding, for any positive $\epsilon$.

Here an ``$\epsilon$-efficient coding'' means that the entropy

Recently Uri Gabor refuted an old conjecture stating that any

finitary factor of an i.i.d process is finitarly isomorphic to an

i.i.d process. Complementing Gabor's result,

in this talk, which is based on work in progress with Yinon Spinka,

we will prove that any countable-valued process which is admits a

finitary a coding by some i.i.d process furthermore admits an

$\epsilon$-efficient finitary coding, for any positive $\epsilon$.

Here an ``$\epsilon$-efficient coding'' means that the entropy

2019
Nov
26

2019
Oct
31

# Basic Notions: Gil Kalai (HUJI) "Classical and quantum computation"

4:00pm to 5:15pm

## Location:

Ross 70

In the lecture I will describe basic notions of computational complexity:

Boolean functions, basic algorithmic tasks, Boolean circuits, P, NP, randomness, quantum circuits, noisy quantum circuits, bounded depth circuits, and more.

If time permits I will describe some (or more realistically one) mathematical challenge in the field and briefly

describe some examples (more realistically, one example) on how theory meets reality.

Boolean functions, basic algorithmic tasks, Boolean circuits, P, NP, randomness, quantum circuits, noisy quantum circuits, bounded depth circuits, and more.

If time permits I will describe some (or more realistically one) mathematical challenge in the field and briefly

describe some examples (more realistically, one example) on how theory meets reality.