2018 Dec 26

# CS theory seminar: Avi Wigderson (IAS) : An invitation to Invariant Theory

## Lecturer:

Avi Wigderson (IAS)
10:30am to 12:00pm

## Location:

Rothberg (CS building) B-220

### Theory of Computer Science Seminar

This talk provides a gentle, high level introduction to (the beautiful) Invariant Theory, that is aimed at non-experts. It will describe some of its main objects, problems and results.

2018 Dec 25

# Ofer Shwartz (Weizmann) Convergence along the cutting-sequences of the geodesic flow

2:15pm to 3:15pm

## Location:

Ross 70
The geodesic flow on a normal cover of a compact hyperbolic surface admits a "random walk" on the group of decks transformations $G$. In this talk, I'll provide some recent results which connect this walk to the geometric properties of the cover and $G$.
2018 Dec 25

# T&G: Or Hershkovits (Stanford), Mean Curvature Flow of Surfaces -- NOTE special time and location

1:00pm to 2:00pm

## Location:

Room 70, Ross Building, Jerusalem, Israel
In the last 35 years, geometric flows have proven to be a powerful tool in geometry and topology. The Mean Curvature Flow is, in many ways, the most natural flow for surfaces in Euclidean space. In this talk, which will assume no prior knowledge, I will illustrate how mean curvature flow could be used to address geometric questions.
2019 Jan 11

# Joram Seminar: Lev Buhovski (Tel-Aviv University) - 0,01% Improvement of the Liouville property for discrete harmonic functions on Z^2.

11:45am to 12:45pm

## Location:

Manchester Building (Hall 2), Hebrew University Jerusalem
Let u be a harmonic function on the plane. The Liouville theorem claims that if |u| is bounded on the whole plane, then u is identically constant. It appears that if u is a harmonic function on the lattice Z^2, and |u| < 1 on 99,99% of Z^2, then u is a constant function. Based on a joint work with A. Logunov, Eu. Malinnikova and M. Sodin.
2018 Dec 31

# Combinatorics: Zur Luria (JCE) "On the threshold for simple connectivity in random 2-complexes"

11:00am to 1:00pm

## Location:

CS bldg, room B500, Safra campus Givat Ram
Speaker: Zur Luria, JCE Title: On the threshold for simple connectivity in random 2-complexes Abstract:
2018 Dec 24

# Combinatorics: Benny Sudakov, ETH, TBA

11:00am to 1:00pm

## Location:

Rothberg CS room B500, Safra campus, Givat Ram
Speaker: Benny Sudakov, ETH, Zurich Title: Subgraph statistics Abstract: Consider integers $k,\ell$ such that $0\le \ell \le \binom{k}2$. Given a large graph $G$, what is the fraction of $k$-vertex subsets of $G$ which span exactly $\ell$ edges? When $G$ is empty or complete, and $\ell$ is zero or $\binom k 2$, this fraction can be exactly 1. On the other hand if $\ell$ is not one these extreme values, then by Ramsey's theorem, this fraction is strictly smaller than 1. The systematic study of the above question was recently initiated by
2018 Dec 17

# Combinatorics: Wojciech Samotij (TAU) "Subsets of posets minimising the number of chains"

11:00am to 1:00pm

## Location:

Rothberg CS bldg, room B500, Safra campus, Givat Ram
Speaker: Wojciech Samotij, TAU Title: Subsets of posets minimising the number of chains Abstract:
2019 Jan 10

# Joram Seminar: Larry Guth (MIT) - Restriction theory and wave packets

4:00pm to 5:15pm

## Location:

Manchester Building (Hall 2), Hebrew University Jerusalem
The proof of decoupling grew out of an area of Fourier analysis called restriction theory. In this talk, we will describe some of the basic problems and tools of restriction theory, especially wave packets, which are a crucial idea in the proof of decoupling.
2018 Dec 17

# NT & AG - Sazzad Biswas

2:30pm to 3:30pm

## Location:

Ross 70

Title: Local root numbers for Heisenberg representations

Abstract: On the Langlands program, explicit computation of the local root numbers
(or epsilon factors) for Galois representations is an integral part.
But for arbitrary Galois representation of higher dimension, we do not
have explicit formula for local root numbers. In our recent work
(joint with Ernst-Wilhelm Zink) we consider Heisenberg representation
(i.e., it represents commutators by scalar matrices) of the Weil
2018 Dec 13

# Basic Notions: Sergiu Hart - "Game Dynamics and Equilibria"

4:00pm to 5:00pm

## Location:

Ross 70
The general theme is game dynamics leading to equilibrium concepts. The plan is to deal with the following topics (all concepts will be defined, and proofs / proof outlines will be provided): (1) An integral approach to the construction of calibrated forecasts and their use for Nash equilibrium dynamics. (2) Blackwell's Approachability Theorem and its use for correlated equilibrium dynamics (regret-matching). (3) Communication complexity and its use for the speed of convergence of uncoupled dynamics.
2018 Dec 20

# Basic Notions: Sergiu Hart - "Game Dynamics and Equilibria"

4:00pm to 5:00pm

## Location:

Ross 70
The general theme is game dynamics leading to equilibrium concepts. The plan is to deal with the following topics (all concepts will be defined, and proofs / proof outlines will be provided): (1) An integral approach to the construction of calibrated forecasts and their use for Nash equilibrium dynamics. (2) Blackwell's Approachability Theorem and its use for correlated equilibrium dynamics (regret-matching). (3) Communication complexity and its use for the speed of convergence of uncoupled dynamics.
2018 Dec 04

# T&G: Pierrick Bousseau (ETH - ITS), Quivers and curves

2:00pm to 3:30pm

## Location:

Room 209, Manchester Building, Jerusalem
I will talk about old and new results relating curve counting on complex surfaces and quiver representations.
2018 Dec 26

# Set Theory Seminar - Ur Yaar (The Modal Logic of Forcing)

2:00pm to 3:30pm

## Location:

Ross 63
Title: The Modal Logic of Forcing

Abstract: Modal logic is used to study various modalities, i.e. various ways in which statements can be true, the most notable of which are the modalities of necessity and possibility. In set-theory, a natural interpretation is to consider a statement as necessary if it holds in any forcing extension of the world, and possible if it holds in some forcing extension. One can now ask what are the modal principles which captures this interpretation, or in other words - what is the "Modal Logic of Forcing"?