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Series: Research Horizons Seminar

Hosts: Amey Kaloti and Ricardo Restrepo

I will state two different inequalities which are poorly understood, even utterly mysterious. They are stated purely in terms of conditional expectations over dyadic intervals. Motivations and connections carry one into the area of Furstenberg's multilinear ergodic averages.

Series: Research Horizons Seminar

Hosts: Amey Kaloti and Ricardo Restrepo

Gauge theory is a beautiful subject that studies the space of connections on a vector bundle. It is also the natural language in which theories of particle physics are formulated. In fact, the word "gauge" has its origins in electromagnetism, and in this talk, we explore the basic geometric objects of gauge theory and show how one explicitly recovers the classical Maxwell's equations as a special case of the equations of gauge theory . Next, generalizing Maxwell's equations to a ``nonabelian" setting, we obtain the Yang-Mills equations, which describe the electroweak force in nature. Surprisingly, these equations were used by Simon Donaldson in the 1980s to prove spectacular results for the topology of smooth four-manifolds. We conclude this talk by describing some of the beautiful geometry and analysis behind gauge theory that goes into the work of Donaldson (for which we awarded a Fields Medal), and time permitting, we hope to say a bit about other gauge-theoretic applications to low-dimensional topology, for instance, instanton Floer homology.

Series: Research Horizons Seminar

Hosts: Yao Li and Ricardo Restrepo

Ulam's problem has to do with finding asymptotics, as $n \to +\infy$, for the length of the longest increasing subsequence of a random permutation of $\{1, .., n\}. I'll survey its history, its solutions and various extensions emphasizing progresses made at GaTech.

Series: Research Horizons Seminar

Hosts: Yao Li and Ricardo Restrepo

Suppose you want to stir a pot of soup with several spoons. What is the most efficient way to do this? Thurston's theory of surface homeomorphisms gives us a concrete way to analyze this question. That is, to each mixing pattern we can associate a real number called the entropy. We'll start from scratch with a simple example, state the Nielsen-Thurston classification of surface homeomorphisms, and give some open questions about entropies of surface homeomorphisms.

Series: Research Horizons Seminar

Hosts: Yao Li and Ricardo Restrepo.

Dr. Millman is the Director of the Center for Education Integrating Science, Mathematics & Computing (CEISMC) and professor of mathematics at the Georgia Institute of Technology. He is a first hand expert in mathematics education and K-12 mathematics teacher education. Complementing the previous panel discussion on jobs in academia and industry, Dr. Milman will lead the discussion on teaching jobs.

Series: Research Horizons Seminar

Hosts: Yao Li and Ricardo Restrepo

Modern Economic Theory is largely based on the concept of Nash Equilibrium. In its simplest form this is an essentially statics notion. I'll introduce a simple model for the origin of money (Kiotaki and Wright, JPE 1989) and use it to introduce a more general (dynamic) concept of Nash Equilibrium and my understanding of its relation to Dynamical Systems Theory and Statistical Mechanics.

Series: Research Horizons Seminar

Hosts: Yao Li and Ricardo Restrepo

We consider compressible fluid flows in Lagrangian coordinates in one space dimension. We assume that the fluid self-interacts through a force field generated by the fluid. We explain how this flow can be described by a differential inclusion on the space of transport maps, when the sticky particle dynamics is assumed. We prove a stability result for solutions of this system. Global existence then follows from a discrete particle approximation.

Series: Research Horizons Seminar

Hosts: Yao Li and Ricardo Restrepo

This will be an expository talk on the study of orthogonal polynomials on the real line and on the unit circle. Topics include recurrence relations, recurrence coefficients and simple examples. The talk will conclude with applications of orthogonal polynomials to other areas of research.

Series: Research Horizons Seminar

Hosts: Yao and Ricardo

Consider self-adjoint operators $A, B, C : \mathcal{H} \to \mathcal{H}$ on a finite-dimensional Hilbert space such that $A + B + C = 0$. Let $\{\lambda_j (A)\}$, $\{\lambda_j (B)\}$, and $\{\lambda_j (C)\}$ be sequences of eigenvalues of $A, B$, and $C$ counting multiplicity, arranged in decreasing order. In 1962, A. Horn conjectured that the relations of $\{\lambda_j (A)\}$,$\{\lambda_j (B)\}$, and $\{\lambda_j (C)\}$ can be characterized by a set of inequalities defined inductively. This problem was eventually solved by A. Klyachko and Knutson-Tao in the late 1990s. Recently together with H. Bercovici, Collins, Dykema, and Timotin, we are able to find a proof to show that the inequalities are valid for self-adjoint elements that satisfies the relation $A+B+C=0$, and the proof can be applied to finite von Neumann algebra. The major difficulty in our argument is to show that certain generalized Schubert cells have nonempty intersection. In the finite dimensional case, it follows from the classical intersection theory. However, there is no readily available intersection theory for von Neumann algebras. Our argument requiresa good understanding of the combinatorial structure of honeycombs, and produces an actual element in the intersection algorithmically, and it seems to be new even in finite dimensions.

Series: Research Horizons Seminar

Hosts: Yao Li and Ricardo Restrepo

The Research Horizons seminar this week will be a panel discussion on the job market for mathematicians. Professor Doug Ulmer and Luca Dieci will give a presentation with general information on the academic job market and the experience of our recent students, in and out of academia. The panel will then take questions from the audience.