Eventss

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 Jan 24

Logic Seminar - Vadim Kulikov - Borel Reducibility in Generalised Descriptive Set Theory"

11:00am to 1:00pm

Location: 

Ross 63

I will review some recent results in the Borel reducibility on uncountable cardinals of the Helsinki logic group.
Borel reducibility on the generalised Baire space \kappa^\kappa for uncountable \kappa is defined analogously to that for \kappa=\omega. One of the corollaries of this work is that under some mild cardinality assumptions on kappa, if T1 is classifiable and T2 is unstable or superstable with OTOP, then the ISOM(T1) is continuously reducible ISOM(T2) and ISOM(T2) is not Borel reducible to ISOM(T1).
2018 Jun 06

Logic Seminar - Gabriel Conant - "Local NIP group theory and pseudofinite groups"

11:00am to 1:00pm

Location: 

Ross 63
Much of the early development of model theoretic stability theory was motivated by stable groups, which include algebraic groups as guiding examples. Later work of Hrushovski and Pillay showed that many tools from stable group theory can be adapted to the local setting, where one works around a single stable formula rather than a stable theory. More recently, groups definable in NIP theories have been intensively studied, bringing back the importance of measures in model theory. On the other hand, local NIP group theory is not as well understood.

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