## Seminars and Colloquia by Series

### Smooth ergodic theory for evolutionary PDE

Series
PDE Seminar
Time
Tuesday, January 24, 2023 - 15:00 for 1 hour (actually 50 minutes)
Location
Skiles 006
Speaker
Alex BluementhGeorgia Tech

Smooth ergodic theory provides a framework for studying systems exhibiting dynamical chaos, features of which include sensitive dependence with respect to initial conditions, correlation decay (even for deterministic systems!) and complicated fractal-like attractor geometry. This talk will be an overview of some of these ideas as they apply to evolutionary PDE, with an emphasis on dissipative semilinear parabolic problems, and a discussion of some of my work in this direction, joint with: Lai-Sang Young and Sam Punshon-Smith.

### On the homology of Torelli groups

Series
Geometry Topology Seminar
Time
Monday, January 23, 2023 - 14:00 for 1 hour (actually 50 minutes)
Location
Skiles 006
Speaker
Dan MinahanGeorgia Institute of Technology

The Torelli group of a surface is a natural yet mysterious subgroup of the mapping class group.  We will discuss a few recent results about finiteness properties of the Torelli group, as well as a result about the cohomological dimension of the Johnson filtration.

### Effective equations for large systems of particles or waves

Series
Job Candidate Talk
Time
Monday, January 23, 2023 - 11:00 for 1 hour (actually 50 minutes)
Location
Skiles Room 006
Speaker
Ioakeim AmpatzoglouNYU Courant Institute

Understanding the behavior of large physical systems is a problem of fundamental importance in mathematical physics. Analysis of systems of many interacting particles is key for understanding various phenomena from physical sciences (e.g. gases in non-equilibrium, galactic dynamics) to social sciences (e.g. modeling social networks). Similarly, the description of systems of weakly nonlinear interacting waves, referred to as wave turbulence theory, finds a wide range of applications from solid state physics and water waves to plasma theory and oceanography. However, with the size of the system of interest being extremely large, deterministic prediction of its behavior is practically impossible, and one resorts to an averaging description. In this talk, we will discuss about kinetic theory, which is a mesoscopic framework to study the qualitative properties of large systems. As we will see, the main idea behind kinetic theory is that, in order to identify averaging quantities of large systems, one studies their asymptotic behavior as the size of the system tends to infinity, with the hope that the limiting effective equation will reveal properties observed in a system of large, but finite size. We will focus on the Boltzmann equation, which is the effective equation for systems of interacting particles, and its higher order extensions, as well as the kinetic wave equation which describes systems of many nonlinearly interacting waves.

### Characteristic sets of matroids and one-dimensional groups

Series
Algebra Seminar
Time
Monday, January 23, 2023 - 10:20 for 1.5 hours (actually 80 minutes)
Location
Skiles 005
Speaker
Dustin CartwrightUniversity of Tennessee

Algebraic matroids record the algebraic dependencies among elements in a field extension, similar to the linear dependencies of vectors in a vector space. Realizing a given matroid by elements in a field extension can depend on the characteristic of the field. I will talk about the possible characteristic sets of algebraic matroids. An essential tool is the one-dimensional group construction of an algebraic matroid, which turns the realization problem for algebraic matroids into a linear problem over the endomorphism ring of a one-dimensional algebraic group.

### Multiserver Stochastic Scheduling: Analysis and Optimization

Series
ACO Student Seminar
Time
Friday, January 20, 2023 - 13:00 for 1 hour (actually 50 minutes)
Location
ONLINE
Speaker
Isaac GrosofCMU

Large-scale computing systems are massively important, using over 1% of the world's electricity. It is vital that these systems be both fast and resource-efficient, and scheduling theory is a key tool towards that goal. However, prior scheduling theory is not equipped to handle large multiserver systems, with little extant theoretical analysis, and no optimality results.

I focus on two important multiserver scheduling systems: The one-server-per-job (M/G/k) model, and the multiple-servers-per-job (MSJ) model. In the M/G/k, we prove the first optimality result, demonstrating that the Shortest Remaining Processing Time (SRPT) policy yields asymptotically optimal mean response time in the heavy traffic limit. In the MSJ model, we prove the first mean response analysis for any scheduling policy, for a novel policy called ServerFilling. Moreover, we introduce the ServerFilling-SRPT policy, for which we present the first asymptotic optimality result for the MSJ model. Each result progresses by proving novel bounds on relevant work, and using novel methods to convert those bounds to bounds on mean response time. These results push the state of the art of scheduling theory ever closer to applicability to today's large-scale computing systems.

### On Extremal Polynomials: 2.Chebyshev Polynomials and Potential Theory

Series
Mathematical Physics and Analysis Working Seminar
Time
Friday, January 20, 2023 - 12:00 for 1 hour (actually 50 minutes)
Location
Skiles 005
Speaker
Burak HatinogluGeorgia Institute of Technology

In the first talk of this series we introduced the definition of Chebyshev polynomials on compact subsets of the complex plane and discussed some properties. This week, after a short review of  the first talk, we will start to discuss asymptotic properties of Chebyshev polynomials and how they are related with logarithmic potential theory. Our main focus will be the necessary concepts from potential theory needed in the study of asymptotic properties of Chebyshev polynomials.

### Complexity and asymptotics in Algebraic Combinatorics

Series
Job Candidate Talk
Time
Thursday, January 19, 2023 - 11:00 for 1 hour (actually 50 minutes)
Location
Skiles 006 and Zoom
Speaker
Greta PanovaUniversity of Southern California

Please Note: Refreshments available from 10:30 in Skiles Atrium. Talk will be streamed via https://gatech.zoom.us/j/94839708119?pwd=bmE1WXFTTzdFVDBtYzlvWUc3clFlZz09 but not recorded.

Algebraic Combinatorics originated in Algebra and Representation Theory, yet its objects and methods turned out applicable to other fields from Probability to Computer Science. Its flagship hook-length formula for the number of Standard Young Tableaux, or the beautiful Littlewood-Richardson rule have inspired large areas of study and development. We will see what lies beyond the reach of such nice product formulas and combinatorial interpretations and enter the realm of Computational Complexity and Asymptotics. We will also show how an 80 year old open problem on Kronecker coefficients of the Symmetric group lead to the disprove of the wishful approach towards the resolution of the algebraic P vs NP Millennium problem.

### Weighted Inequalities for Singular Integral Operators

Series
Analysis Seminar
Time
Wednesday, January 18, 2023 - 14:00 for 1 hour (actually 50 minutes)
Location
Skiles 268
Speaker
Manasa VempatiGeorgia Tech

Weighted inequalities for singular integral operators are central in the study of non-homogeneous harmonic analysis. Two weight inequalities for singular integral operators, in-particular attracted attention as they can be essential in the perturbation theory of unitary matrices, spectral theory of Jacobi matrices and PDE's. In this talk, I will discuss several results concerning the two weight inequalities for various Calder\'on-Zygmund operators in both Euclidean setting and in the more generic setting of spaces of homogeneous type in the sense of Coifman and Weiss.

The two-weight conjecture for singular integral operators T was first raised by Nazarov, Treil and Volberg on finding the real variable characterization of the two weights u and v so that T is bounded on the weighted $L^2$ spaces. This conjecture was only solved completely for the Hilbert transform on R until recently. In this talk, I will describe our result that resolves a part of this conjecture for any Calder\'on-Zygmund operator on the spaces of homogeneous type by providing a complete set of sufficient conditions on the pair of weights. We will also discuss the existence of similar analogues for multilinear Calder\'on-Zygmund operators.

### Bias in cubic Gauss sums: Patterson's conjecture

Series
Job Candidate Talk
Time
Wednesday, January 18, 2023 - 11:05 for 1 hour (actually 50 minutes)
Location
Skiles 006
Speaker
Alexander DunnCaltech

Large sieve inequalities are a fundamental tool used to investigate prime numbers and exponential sums. I will explain my work that resolves a 1978 conjecture of S. Patterson (conditional on the Generalized Riemann hypothesis) concerning the bias of cubic Gauss sums. This explains a well-known numerical bias first observed by Kummer in 1846. One important byproduct of my work is a proof that

Heath-Brown's famous cubic large sieve is sharp, contrary to popular belief.  This sheds light on some of the mysteries surrounding large sieve inequalities for certain families of arithmetic harmonics and gives strong clues on where to look next for further progress. This is based on joint work with Maksym Radziwill.

### Non-uniqueness and convex integration for the forced Euler equations

Series
PDE Seminar
Time
Tuesday, January 17, 2023 - 15:00 for 1 hour (actually 50 minutes)
Location
Skiles 006
Speaker
Stan PalasekUCLA

This talk is concerned with α-Hölder-continuous weak solutions of the incompressible Euler equations. A great deal of recent effort has led to the conclusion that the space of Euler flows is flexible when α is below 1/3, the famous Onsager regularity. We show how convex integration techniques can be extended above the Onsager regularity to all α<1/2 in the case of the forced Euler equations. This leads to a new non-uniqueness theorem for any initial data. This work is joint with Aynur Bulut and Manh Khang Huynh.