2018 Jun 26

# Dynamics Lunch: Jasmin Matz (Huji) ״Distribution of periodic orbits of the horocycle flow״

12:00pm to 1:00pm

## Location:

Manchester lounge
An old result of Hedlund tells us that there are no closed orbits for the horocycle flow on a compact Riemann surface M. The situation is different if M is non-compact in which case there is a one-parameter family of periodic orbits for every cusp of M. I want to talk about a result by Sarnak concerning the distribution of the such orbits in each of these families when their length goes to infinity. It turns out that these orbits become equidistributed in M and the rate of convergence can in fact be quantified in terms of spectral properties of the Eisenstein series on M.
2018 May 03

# Special Talk : W Chacholski (Copenhagen) - "What is persistence?"

## Lecturer:

W Chacholski (Copenhagen)
1:15pm to 2:00pm

Ross 63
2018 May 03

# Basic Notions - Alex Lubotzky: "Group stability and approximation"

4:00pm to 5:30pm

## Location:

Ross 70
An old problem (Going back to Turing, Ulam and others) asks about the "stability" of solutions in some algebraic contexts. We will discuss this general problem in the context group theory: Given an "almost homomorphism" between two groups, is it close to a homomorphism?
2018 May 22

# Barak Weiss (TAU): New examples for the horocycle flow on the moduli space of translation surfaces

2:15pm to 3:15pm

A longstanding open question concerning the horocycle flow on moduli space of translation surfaces, is whether one can classify the invariant measures and orbit-closures for this action. Related far-reaching results of Eskin, Mirzakhani and Mohammadi indicated that the answer might be positive. However, in recent work with Jon Chaika and John Smillie, we find unexpected examples of orbit-closures; e.g. orbit closures which are not generic for any measure, and others which have fractional Hausdorff dimension. Such examples exist even in genus 2.
2018 Jun 11

# Combinatorics: Chris Cox (CMU) "Nearly orthogonal vectors"

11:00am to 12:30pm

## Location:

IIAS, Eilat hall, Feldman bldg, Givat Ram
Speaker: Chris Cox, CMU
Title -- Nearly orthogonal vectors

2018 Jun 05

# Dynamics Lunch: Hagai Lavner (Huji)

12:00pm to 1:00pm

## Location:

Manchester lounge
2018 Jun 19

# Tomasz Rzepecki (Uniwersytet Wrocławski): Topological dynamics and Galois groups in model theory

2:15pm to 3:15pm

## Location:

Ross 70
In recent years, topological dynamics have become an important tool in model theory. I will talk about some topological dynamical results from my PhD thesis about the so-called group-like equivalence relations. I plan to give a glimpse of the motivations in model theory (mostly related to the model-theoretic Galois groups and connected components of definable groups) and to show some ideas of the proofs.
I will briefly recall the required notions from topological dynamics. Some knowledge of model theory will help to understand the motivations, but otherwise, it will not be necessary.