Homological versus Hodge-theoretic mirror symmetry

Timothy Perutz
University of Texas, Austin; von Neumann Fellow, School of Mathematics
January 30, 2017
I'll describe joint work with Sheel Ganatra and Nick Sheridan which rigorously establishes the relationship between different aspects of the mirror symmetry phenomenon for Calabi-Yau manifolds. Homological mirror symmetry---an abstract, categorical statement---implies Hodge theoretic mirror symmetry, a concrete relation between counts of rational curves and variations of Hodge structure.

Quantifying tradeoffs between fairness and accuracy in online learning

Aaron Roth
University of Pennsylvania
January 30, 2017
In this talk, I will discuss our recent efforts to formalize a particular notion of “fairness” in online decision making problems, and study its costs on the achievable learning rate of the algorithm. Our focus for most of the talk will be on the “contextual bandit” problem, which models the following scenario. Every day, applicants from different populations submit loan applications to a lender, who must select a subset of them to give loans to.

Large coupling asymptotics for the Lyapunov exponent of quasi-periodic Schrödinger operators with analytic potentials

Christoph Marx
Oberlin College
January 25, 2017
In this talk we will quantify the coupling asymptotics for the Lyapunov exponent (LE) of a one-frequency quasi-periodic Schrödinger operator with analytic potential sampling function. By proving an asymptotic formula for the LE valid for all irrational frequencies, our result refines the well-known lower bound by Sorets and Spencer.

Reinforced random walks and statistical physics

Pierre Tarres
Université Paris-Dauphine
January 24, 2017
We explain how the Edge-reinforced random walk, introduced by Coppersmith and Diaconis in 1986, is related to several models in statistical physics, namely the supersymmetric hyperbolic sigma model studied by Disertori, Spencer and Zirnbauer (2010), the random Schrödinger operator and Dynkin's isomorphism. These correspondences enable us to show recurrence/transience results on the Edge-reinforced random walk, and they also allow us to provide insight into these models.

Active learning with "simple" membership queries

Shachar Lovett
University of California, San Diego
January 23, 2017
An active learning algorithm for a classification problem has access to many unlabelled samples. The algorithm asks for the labels of a small number of samples, carefully chosen, such that that it can leverage this information to correctly label most of the unlabelled samples. It is motivated by many real world applications, where it is much easier and cheaper to obtain access to unlabelled data compared to labelled data. The main question is: can active learning algorithms out-perform classic passive learning algorithms?

Constructible sheaves in mirror symmetry

David Treumann
Boston College; von Neumann Fellow, School of Mathematics
January 20, 2017
I will survey the coherent-constructible correspondence of Bondal, which embeds the derived category of coherent sheaves on a toric variety into the derived category of constructible sheaves on a compact torus. The tools of the first lecture turn this into a homological mirror theorem -- a pretty strong one, after recent results of Ike and Kuwagaki.

Constructible sheaves in symplectic topology

David Treumann
Boston College; von Neumann Fellow, School of Mathematics
January 18, 2017

I will give an introduction to the microlocal theory of sheaves after Kashiwara and Schapira, and some of its recent applications in symplectic topology. I'll start with the basics, but target applications for the 75 minutes are Tamarkin's proof of nondisplaceability, and Shende's proof that a Legendrian isotopy between conormals of knots implies a smooth isotopy between the knots.