2018 May 29

# Dynamics Lunch: Matan Seidel (Huji) - "The Mass Transport Principle in Percolation Theory"

12:00pm to 1:00pm

## Location:

Manchester lounge
The Mass Transport Principle is a useful technique that was introduced to the study of automorphism-invariant percolations by Häggström in 1997. The technique is a sort of mass conservation principle, that allows us to relate random properties (such as the random degree of a vertex) to geometric properties of the graph.
I will introduce the principle and the class of unimodular graphs on which it holds, as well as a few of its applications.
2018 Apr 16

# Special talk: Yonatan Harpaz (Paris 13) - "Towards a universal property for Hermitian K-theory"

## Lecturer:

Yonatan Harpaz (Paris 13)
4:30pm to 5:30pm

## Location:

Ross 70

Abstract: Hermitian K-theory can be described as the "real" analogue of algebraic K-theory, and plays a motivic role similar to the role played by real topological K-theory in classical stable homotopy theory. However, the abstract framework surrounding and supporting Hermitian K-theory is less well understood than its algebraic counterpart, especially in the case when 2 is not assumed to be invertible in the ground ring.

2018 Jun 27

# Analysis Seminar: Barry Simon (Caltech) "Heinävarra’s Proof of the Dobsch–Donoghue Theorem"

12:00pm to 1:00pm

## Location:

Ross Building, Room 70
Abstract:
In 1934, Loewner proved a remarkable and deep theorem about matrix monotone functions. Recently, the young Finnish mathematician, Otte Heinävarra settled a 10 year old conjecture and found a 2 page proof of a theorem in Loewner theory whose only prior proof was 35 pages. I will describe his proof and use that as an excuse to discuss matrix monotone and matrix convex functions including, if time allows, my own recent proof of Loewner’s original theorem.
2018 May 29

# Yuri Lima (Paris 11): Symbolic dynamics for non-uniformly hyperbolic systems with singularities

2:15pm to 3:15pm

## Location:

Ross 70
Symbolic dynamics is a tool that simplifies the study of dynamical systems in various aspects. It is known for almost fifty years that uniformly hyperbolic systems have good'' codings. For non-uniformly hyperbolic systems, Sarig constructed in 2013 good'' codings for surface diffeomorphisms. In this talk we will discuss some recent developments on Sarig's theory, when the map has discountinuities and/or critical points, such as multimodal maps of the interval and Bunimovich billiards.
2018 May 08

# Dynamics Seminar: Yinon Spinka (TAU): Finitary codings of Markov random fields

2:15pm to 4:15pm

## Location:

Ross 70

Let X be a stationary Z^d-process. We say that X is a factor of an i.i.d. process if there is a (deterministic and translation-invariant) way to construct a realization of X from i.i.d. variables associated to the sites of Z^d. That is, if there is an i.i.d. process Y and a measurable map F from the underlying space of Y to that of X, which commutes with translations of Z^d and satisfies that F(Y)=X in distribution. Such a factor is called finitary if, in order to determine the value of X at a given site, one only needs to look at a finite (but random) region of Y.
2018 Apr 12

# Special talk: Yonatan Harpaz (Paris 13) - "Small extensions in algebra and topology"

## Lecturer:

Yonatan Harpaz (Paris 13)
1:15pm to 2:15pm

## Location:

Ross 70
Abstract: In this talk, we will discuss the notion of small extensions in its various incarnations, from torsors under abelian groups to square-zero extensions of algebras. We will then focus on the somewhat less familiar case of small extensions of ∞-categories. Our main goal is to make this abstract concept concrete and intuitive through a variety of examples. In particular, we will advocate the point of view that small extensions of  ∞-categories offer a unifying perspective in understanding many constructions appearing in obstruction, classification, and deformation theoretic problems
2018 Apr 16

# HD-Combinatorics Special Day on Grassman Expanders and Unique Games (organized by Irit Dinur)

(All day)

## Location:

Room 130, IIAS, Feldman Building, Givat Ram
2018 Apr 11

4:00pm to 6:00pm

Ross 70A
2018 Apr 15

# GAME THEORY AND MATHEMATICAL ECONOMICS RESEARCH SEMINAR: Ron Peretz, Bar Ilan University: "The Rate of Innovation Diffusion in Social Networks (joint with Itai Arieli, Yakov Babichenko, and Peyton H Young)"

1:30pm to 2:30pm

## Location:

Elath Hall, 2nd floor, Feldman Building, Edmond Safra Campus
2018 May 22

# Dynamics Lunch: Tsviqa Lakrec (Huji)

12:00pm to 1:00pm

## Location:

Manchester lounge
2018 May 09

# Logic Seminar - Immanuel Benporat - "Arbault sets"

11:00am to 1:00pm

## Location:

Ross 63
Arbault sets (briefly, A-sets) were first introduced by Jean Arbault in the context of Fourier analysis. One of his major results concerning these sets,asserts that the union of an A-set with a countable set is again an A-set. The next obvious step is to ask what happens if we replace the word "countable" by א_1. Apparently, an א_1 version of Arbault's theorem is independent of ZFC. The aim of this talk would be to give a proof (as detailed as possible) of this independence result. The main ingredients of the proof are infinite combinatorics and some very basic Fourier analysis.
2016 Dec 27

# Special logic seminar - Itaï BEN YAACOV, "Baby version of the asymptotic volume estimate"

10:00am to 12:00pm

## Location:

Shprinzak 102
I'll show how the Vandermonde determinant identity allows us to
estimate the volume of certain spaces of polynomials in one variable
(or rather, of homogeneous polynomials in two variables), as the degree
goes to infinity.
I'll explain what this is good for in the context of globally valued
fields, and, given time constraints, may give some indications on the
approach for the "real inequality" in higher projective dimension.
2018 May 23

# Logic Seminar - Alejandro Poveda Ruzafa - "A Magidor-like study of $C^{(n)}$-cardinals"

11:00am to 1:00pm

## Location:

Ross 63
The notion of reflection plays a central role in modern Set Theory since the descovering of the well-known Lévy and Montague \textit{Reflection principle}. For any $n\in\omega$, let $C^{(n)}$ denote the class of all ordinals $\kappa$ which correctly interprets the $\Sigma_n$-statements of the universe, with parametes in $V_\kappa$.
2017 Mar 15

# Logic seminar - Rizos Sklinos, "Non-equational stable groups"

4:00pm to 6:00pm

## Location:

Ross 70
Non-equational stable groups.
Speaker: Rizos Sklinos
Abstract: The notion of equationality has been introduced by Srour and further
developed by Pillay-Srour. It is best understood intuitively as a notion
of Noetherianity on instances of first-order formulas. A first-order
theory is equational when every first-order formula is equivalent to a
boolean combination of equations.
Equationality implies stability and for many years these two notions were
identified, as only an "artificial" example of Hrushovski (a tweaked