• Speaker: Lucas Hall, MSU
• Title: Skew Products: Coactions You Can See
• Date: 09/06/2022
• Time: 11:00 AM - 11:50 AM
• Place: C304 Wells Hall
• Contact: Brent Nelson (banelson@msu.edu)

The speaker introduces topological quivers and constructs their associated C*-algebra. We present two independent constructions which arise in the presence of a cocycle (the topological ”skew product" and the algebraic coaction) and show that the constructions agree in a suitable sense. Along the way, we characterize the skew product based on some associated topological dynamics. Time permitting, we will explore future directions.

• Speaker: G&T Seminar, MSU
• Title: Organizational Meeting
• Date: 09/06/2022
• Time: 3:00 PM - 4:00 PM
• Place: C304 Wells Hall (Virtual Meeting Link)
• Contact: Vijay B Higgins (higgi231@msu.edu)

Organizational meeting for the GT seminar this Fall.

• Speaker: Sasha Volberg, MSU
• Title: Heat smoothing conjecture and Bernstein--Markov inequalities on Hamming cube
• Date: 09/07/2022
• Time: 4:10 PM - 5:00 PM
• Place: C304 Wells Hall
• Contact: Willie Wai-Yeung Wong (wongwil2@msu.edu)

Hamming cube and its various Poincaré type inequalities represent a crucial model for many questions ranging from Banach space theory to graph theory to theoretical computer science. We present some estimates for tail spaces on Hamming cube. We use the analytic paraproduct operator for that. We also show some Bernstein--Markov inequalities, here the novelty is in getting rid of some irritating logarithms.

• Speaker: Lara Pudwell, Valparaiso University
• Title: Pattern-avoiding parking functions
• Date: 09/08/2022
• Time: 3:00 PM - 3:50 PM
• Place: Online (virtual meeting) (Virtual Meeting Link)
• Contact: Bruce E Sagan (bsagan@msu.edu)

We extend the classical definition of patterns in permutations to parking functions. In particular we study parking functions that avoid permutations of length 3. A number of well-known combinatorial sequences arise in our analysis, and this talk will highlight several bijective results. This project is joint work with Ayomikun Adeniran.

• Speaker: Leonid Parnovski, University College London
• Title: Floating mats and sloping beaches: spectral asymptotics of the Steklov problem on polygons
• Date: 09/08/2022
• Time: 4:10 PM - 5:00 PM
• Place: C304 Wells Hall
• Contact: Joseph Waldron (waldro51@msu.edu)

I will discuss asymptotic behaviour of the eigenvalues of the Steklov problem (aka Dirichlet-to-Neumann operator) on curvilinear polygons. The answer is completely unexpected and depends on the arithmetic properties of the angles of the polygon.

• Speaker: Leonid Chekhov, Michigan State University
• Title: Symplectic groupoid and cluster algebra description of closed Riemann surfaces
• Date: 09/12/2022
• Time: 12:30 PM - 1:30 PM
• Place: C304 Wells Hall
• Contact: Linhui Shen (shenlin1@msu.edu)

We use the Fock-Goncharov higher Teichmuller space directed networks to solve the symplectic groupoid condition: parameterize pairs of $SL_n$ matrices (B,A) with A unipotent such that $BAB^T$ is also unipotent. A natural Lie-Poisson bracket on B generates the Goldman bracket on elements of A and $BAB^T$, which are simultaneously elements of the corresponding upper cluster algebras. Using this input we identify the space of X-cluster algebra elements with Teichmuller spaces of closed Riemann surfaces of genus 2 (for $n$=3) and 3 (for $n$=4) endowed with Goldman bracket structure: for $g$=2 all geodesic functions are positive Laurent polynomials and Dehn twists correspond to mutations in the corresponding quivers. This is the work in progress with Misha Shapiro.

• Speaker: Brent Nelson, MSU
• Title: Making Weight
• Date: 09/12/2022
• Time: 4:00 PM - 5:30 PM
• Place: C517 Wells Hall
• Contact: Brent Nelson (banelson@msu.edu)

A weight on a von Neumann algebra is a positive linear map that is permitted to be infinitely valued. It is a generalization of a positive linear functional that arises naturally in the context of crossed products by non-discrete groups, and they are vital to the study of purely infinite von Neumann algebras. In this talk I will provide an introduction to the theory of weights that assumes only the definition of a von Neumann algebra.

• Speaker: Lara Ismert, Embry–Riddle Aeronautical University
• Title: A Liouville-esque theorem for a weakly-defined derivation on B(H)
• Date: 09/13/2022
• Time: 11:00 AM - 11:50 AM
• Place: C304 Wells Hall
• Contact: Brent Nelson (banelson@msu.edu)

Liouville’s Theorem states that any bounded entire function on the complex plane is necessarily constant. In this talk, we discuss an analogous theorem for a weakly-defined derivation on B(H) studied in recent years by Erik Christensen. As a consequence, we provide new sufficient conditions for when two operators which satisfy the Heisenberg Commutation Relation must both be unbounded.

• Speaker: Brendon Rhoades, UCSD
• Title: Superspace, Vandermondes, and representations
• Date: 09/14/2022
• Time: 3:00 PM - 3:50 PM
• Place: Online (virtual meeting) (Virtual Meeting Link)
• Contact: Bruce E Sagan (bsagan@msu.edu)

We present an extension of the Vandermonde determinant from the polynomial ring to superspace. These superspace Vandermondes are used to construct modules over the symmetric group with (occasionally conjectural) connections to geometry and coinvariant theory. Joint with Andy Wilson.

• Speaker: Jie Yang, MSU
• Title: Organizing meeting for Student Number Theory Seminar
• Date: 09/15/2022
• Time: 3:00 PM - 4:00 PM
• Place: C204A Wells Hall
• Contact: Jie Yang (yangji79@msu.edu)

In this first meeting, I'll give some motivations towards the study of p-adic modular forms, and explain some central concepts in "eigenvarieties machine" introduced by K. Buzzard. In the end, we will discuss the plan for this seminar.

• Speaker: Jenny Wilson, University of Michigan
• Title: Stability patterns in configuration spaces
• Date: 09/15/2022
• Time: 4:10 PM - 5:00 PM
• Place: Online (virtual meeting) (Virtual Meeting Link)
• Contact: Olga Turanova (turanova@msu.edu)

This talk will give an introduction of the recent field of 'representation stability'. I will discuss how we can use representation theory to illuminate the structure of certain families of groups or topological spaces with actions of the symmetric groups, focusing on configuration spaces as an illustrative example.

• Speaker: Anna Veselovska, Department of Mathematics, Technical University of Munich, Germany
• Title: Super-Resolution on the Two-Dimensional Unit Sphere
• Date: 09/16/2022
• Time: 4:00 PM - 5:00 PM
• Place: C304 Wells Hall
• Contact: Mark A Iwen (iwenmark@msu.edu)

In this talk, we discuss the problem of recovering an atomic measure on the unit 2-sphere S^2 given finitely many moments with respect to spherical harmonics. The analysis relies on the formulation of this problem as an optimization problem on the space of bounded Borel measures on S^2 as suggested by Y. de Castro & F. Gamboa and E. Candes & C. Fernandez-Granda. We construct a dual certificate using a kernel given in an explicit form and make a concrete analysis of the interpolation problem. We support our theoretical results by various numerical examples related to direct solution of the optimization problem and its discretization. This is a joint work with Frank Filbir and Kristof Schroder.

• Speaker: Alexander Vainshtein, Haifa University
• Title: Cluster structures on SL_n and the Belavin-Drinfeld classification
• Date: 09/19/2022
• Time: 12:30 PM - 1:30 PM
• Place: C304 Wells Hall
• Contact: Michael Shapiro (mshapiro@msu.edu)

Cluster structures were discovered by S. Fomin and A. Zelevinsky about twenty years ago and quickly found applications in various fields of mathematics and mathematical physics. In the latter, several advances were made in a study of classical and quantum integrable systems arising in the context of cluster structures. These systems "live" on Poisson-Lie groups and their Poisson homogeneous spaces, hence it is important to understand an interplay between cluster and Poisson structures on such objects. In this talk I will explain a construction of a family of (generalized) cluster structures in the algebra of regular functions on SL_n related to the Belavin-Drinfeld classification of Poisson-Lie structures on SL_n. Based on a joint work with M.~Gekhtman (Notre Dame) and M.~Shapiro (MSU).

• Speaker: Craig Gross, MSU
• Title: All aboard! A mathematical study of transit equity in Baltimore
• Date: 09/19/2022
• Time: 1:00 PM - 2:00 PM
• Place: C117 Wells Hall (Virtual Meeting Link)
• Contact: Craig Gross (grosscra@msu.edu)

In 2015, the governor of Maryland canceled a light rail project through the city of Baltimore that had been planned and funded for over a decade. Instead, the money was diverted to funding highways near the richer, whiter suburbs of the city. As Baltimore is home to some of the most extreme class-disparity and segregation in the country, this decision significantly hurt the potential for a more equitable transit system. But by how much? $\\$ This talk will be a tour through a mathematical investigation of how the canceled light rail might have increased access to jobs across the city. In particular, we use some dimension-reduction and clustering algorithms on CDC Social Vulnerability Indices to explore which parts of the city may be socioeconomically disadvantaged. We then compute job accessibility metrics to determine how the light rail would have affected these regions. We also give some considerations for converting a collection of many relevant indicators into more interpretable, manageable metrics for future transit studies. $\\$ This is joint work with Adam Lee, Kethaki Varadan, and Yangxinyu Xie. $\\$ This will be a hybrid seminar and take place in C117 Wells Hall and via Zoom at https://msu.zoom.us/j/99426648081?pwd=ZEljM3BPUXg2MjVUMVM5TnlzK2NQZz09 .

• Speaker: Brent Nelson, MSU
• Title: Worth Their Weight
• Date: 09/19/2022
• Time: 4:00 PM - 5:30 PM
• Place: C517 Wells Hall
• Contact: Brent Nelson (banelson@msu.edu)

I will continue my introduction to weights. I will briefly mention equivalent conditions of normality for weights before moving onto a discussion of semi-cyclic representations and Tomita-Takesaki theory. I will conclude with a detailed examination of Plancherel weights on locally compact groups.

• Speaker: Alberto Takase, MSU and UC Irvine
• Title: Spectral estimates of dynamically-defined and amenable operator families (In collaboration with Siegfried Beckus)
• Date: 09/20/2022
• Time: 11:00 AM - 11:50 AM
• Place: C304 Wells Hall
• Contact: Ilya Kachkovskiy (ikachkov@msu.edu)

For dynamically-defined operator families, the Hausdorff distance of the spectra is estimated by the distance of the underlying dynamical systems while the group is amenable. We prove that if the group has strict polynomial growth and both the group action and the coefficients are Lipschitz continuous, then the spectral estimate has a square root behavior or, equivalently, the spectrum map is $\frac{1}{2}$-Holder continuous. We prove the behavior can be improved resulting in the spectrum map being Lipschitz continuous if the coefficients are locally-constant. In 1990, the square root behavior was established for the Almost Mathieu Operator or, more generally, the quasiperiodic operators with Lipschitz continuous potentials. Our results extend the square root behavior to a bigger class of operators such as (magnetic) discrete Schrodinger operators with finite range and with Lipschitz continuous coefficients.

• Speaker: Bin Sun, Oxford
• Title: $L^2$-Betti numbers of fiber bundles
• Date: 09/20/2022
• Time: 3:00 PM - 4:00 PM
• Place: C304 Wells Hall (Virtual Meeting Link)
• Contact: Vijay B Higgins (higgi231@msu.edu)

We study the $L^2$-Betti numbers of fiber bundles $F \rightarrow E \rightarrow B$ of manifolds. Under certain conditions (e.g., when $F$ is simply connected), $b_*^{(2)}(E)$ can be computed using the twisted $L^2$-Betti numbers of $B.$ We relate the twisted and untwisted $L^2$-Betti numbers of $B$ when $\pi_1(B)$ is locally indicable. As an application, we compute $b_*^{(2)}(E)$ when $B$ is either a surface or a non-positively curved $3-$manifold. This is a joint work with Dawid Kielak.

• Speaker: 
• Title: Organizational Meeting
• Date: 09/20/2022
• Time: 4:00 PM - 5:00 PM
• Place: C517 Wells Hall
• Contact: Ivan So (soivan@msu.edu)

No abstract available.

• Speaker: Alex Wilson, Dartmouth
• Title: A Diagram-Like Basis for the Multiset Partition Algebra
• Date: 09/21/2022
• Time: 3:00 PM - 3:50 PM
• Place: Online (virtual meeting) (Virtual Meeting Link)
• Contact: Bruce E Sagan (bsagan@msu.edu)

There's a classical connection between the representation theory of the symmetric group and the general linear group called Schur-Weyl Duality. Variations on this principle yield analogous connections between the symmetric group and other objects such as the partition algebra and more recently the multiset partition algebra. The partition algebra has a well-known basis indexed by graph-theoretic diagrams which allows the multiplication in the algebra to be understood visually as combinations of these diagrams. I will present an analogous basis for the multiset partition algebra and show how this basis can be used to describe generators and construct representations for the algebra.

• Speaker: Michael McNulty, MSU
• Title: Conditionally Stable Self-Similar Blowup for the Supercritical Quadratic Wave Equation Beyond the Light Cone
• Date: 09/21/2022
• Time: 4:10 PM - 5:00 PM
• Place: C304 Wells Hall
• Contact: Willie Wai-Yeung Wong (wongwil2@msu.edu)

Nonlinear wave equations of power-type serve as excellent toy models for geometric PDEs such as the Yang-Mills and wave maps equations. Of great interest in the energy supercritical setting is that of threshold phenomena. In this setting, unstable self-similar blowup solutions are believed to play an essential role in describing the threshold of singularity formation. We will discuss the stability of an explicitly known, unstable self-similar blowup solution of the energy supercritical quadratic wave equation in a region of spacetime which extends beyond the time of blowup. To overcome this instability, we introduce a new canonical method to investigate unstable self-similar solutions. This work represents the first steps toward an understanding of threshold phenomena in the energy supercritical setting.

• Speaker: Rayan Saab, University of California, San Diego (UCSD)
• Title: Quantizing neural networks
• Date: 09/22/2022
• Time: 2:30 PM - 3:30 PM
• Place: Online (virtual meeting) (Virtual Meeting Link)
• Contact: Mark A Iwen (iwenmark@msu.edu)

Neural networks are highly non-linear functions often parametrized by a staggering number of weights. Miniaturizing these networks and implementing them in hardware is a direction of research that is fueled by a practical need, and at the same time connects to interesting mathematical problems. For example, by quantizing, or replacing the weights of a neural network with quantized (e.g., binary) counterparts, massive savings in cost, computation time, memory, and power consumption can be attained. Of course, one wishes to attain these savings while preserving the action of the function on domains of interest. We present data-driven and computationally efficient methods for quantizing the weights of already trained neural networks and we prove that our methods have favorable error guarantees under a variety of assumptions. We also discuss extensions and provide the results of numerical experiments, on large multi-layer networks, to illustrate the performance of our methods. Time permitting, we will also discuss open problems and related areas of research.

• Speaker: Peikai Qi, MSU
• Title: Modular form and Hecke operator1
• Date: 09/22/2022
• Time: 3:00 PM - 4:00 PM
• Place: C204A Wells Hall
• Contact: Peikai Qi (qipeikai@msu.edu)

In the talk, we will review the definition of modular form and hecke algebra.

• Speaker: Chenyang Xu, Princeton University
• Title: K-stability and birational geometry
• Date: 09/22/2022
• Time: 4:10 PM - 5:00 PM
• Place: Online (virtual meeting) (Virtual Meeting Link)
• Contact: Joseph Waldron (waldro51@msu.edu)

The notion of K-stability for a Fano varieties was introduced by differential geometers in late 90s, to capture the existence of a Kähler-Einstein metric. In the last decade, it has gradually become clear to algebraic geometers that K-stability provides a rich algebraic theory in higher dimensional geometry. In particular, it can be used to solve the longstanding question of constructing moduli spaces for Fano varieties. I will survey the background of K-stability and how algebraic geometers’ understanding of it has evolved. In particular, I will explain algebraic geometry plays a key role of establishing the equivalence between K-stability and the existence of a Kähler-Einstein metric, i.e. the Yau-Tian-Donaldson Conjecture, for all Fano varieties. If time permits, I want to also discuss the construction of K-moduli spaces parametrizing Fano varieties, and how the recipe given by K-stability can be used to resolve the issues that mystify people for a long time.

• Speaker: Jiuzu Hong, University of North Carolina at Chapel Hill
• Title: BD Schubert varieties of parahoric group schemes and global Demazure modules of twisted current algebras
• Date: 09/26/2022
• Time: 12:30 PM - 1:30 PM
• Place: C304 Wells Hall
• Contact: Linhui Shen (shenlin1@msu.edu)

It is well-known that there is a duality between affine Demazure modules and the spaces of sections of line bundles on Schubert varieties in affine Grassmannians. This should be regarded as a local theory. In this talk, I will explain an algebraic theory of global Demazure modules of twisted current algebras. Moreover, these modules are dual to the spaces of sections of line bundles on Beilinson-Drinfeld Schubert varieties of certain parahoric groups schemes, where the factorizations of global Demazure modules are compatible with the factorizations of line bundles. This generalizes the work of Dumanski-Feigin-Finkelberg in the untwisted setting. In order to establish this duality in the twisted case, following the works of Zhu, we prove the flatness of BD Schubert varieties, and establish factorizable and equivariant structures on the rigidified line bundles over BD Grassmannians of these parahoric group schemes. This work is joint with Huanhuan Yu.

• Speaker: Remy Liu, MSU
• Title: Understanding dataset characteristics via diffusion on graph
• Date: 09/26/2022
• Time: 1:00 PM - 2:00 PM
• Place: C117 Wells Hall (Virtual Meeting Link)
• Contact: Craig Gross (grosscra@msu.edu)

Classical graph signal processing provides powerful techniques for understanding and modifying graph signals from the spectral domain, but they come with high computational costs. More recently, diffusion on graphs has been sought as an alternative approach to modifying graph signals; it is much more computationally efficient and is easy to interpret from the spatial perspective. Here, we present two different studies utilizing diffusion wavelets on a graph to filter graph signals for downstream analysis. In the first study, we aim to understand how and what is being utilized by Graph Neural Networks to achieve graph-related tasks. We do so by observing the performance difference between using the filtered graph and the original graph. We demonstrate that some image datasets, such as CIFAR and MNIST, rely on low-frequency signals; on the contrary, heterophilic datasets, such as WebKB, rely more heavily on high-frequency signals. In the second study on computational biology using gene interaction networks and gene expression data, we observe similar results where different frequency bands perform differently in a task-specific manner. In summary, our studies demonstrate the practical usage of graph diffusion to modify graph signals, leading to improved downstream prediction performance and a better understanding of the graph datasets' characteristics. $\\$ This will be a hybrid seminar and take place in C117 Wells Hall and via Zoom at https://msu.zoom.us/j/99426648081?pwd=ZEljM3BPUXg2MjVUMVM5TnlzK2NQZz09 .

• Speaker: Patrick Daniels, University of Michigan
• Title: Canonical integral models for Shimura varieties defined by tori
• Date: 09/26/2022
• Time: 3:00 PM - 4:00 PM
• Place: C304 Wells Hall
• Contact: Georgios Pappas (pappasg@msu.edu)

Pappas and Rapoport have recently conjectured the existence of canonical integral models for Shimura varieties with parahoric level structure, which are characterized using Scholze's theory of p-adic shtukas. We will illustrate the conjecture using the example of Shimura varieties defined by tori, where (surprisingly) the theory is already nontrivial. Along the way we will explain a connection with the Bhatt-Scholze theory of prismatic F-crystals.

• Speaker: Aldo Garcia Guinto, MSU
• Title: Conjugate Variables and Dual Systems
• Date: 09/26/2022
• Time: 4:00 PM - 5:30 PM
• Place: C517 Wells Hall
• Contact: Brent Nelson (banelson@msu.edu)

In free probability, the semi-circular operators are the analogue of the Gaussian distribution in classical probability. We will be using the semi-circular operators to motivate two notions of free probability: conjugate variables and dual systems. The conjugate variables are used to define free Fisher information, which is analogue of Fisher information in classical probability. While the dual systems are related to a cohomology theory for von Neumann algebras. It turns out that these two notions are not as different as they may seem.

• Speaker: Ayomikun Adeniran, Colby College
• Title: Parking completions
• Date: 09/28/2022
• Time: 3:00 PM - 3:50 PM
• Place: Online (virtual meeting) (Virtual Meeting Link)
• Contact: Bruce E Sagan (bsagan@msu.edu)

Parking functions are well-known objects in combinatorics. One interesting generalization of parking functions are parking completions. A parking completion corresponds to a set of preferences where all cars park assuming some of the spots on the street are already occupied. In this talk, we will explore how parking completions are related to restricted lattice paths. We will also present results for both the ordered and unordered variations of the problem by use of a pair of operations (termed Join and Split). A nice consequence of our results is a new volume formula for most Pitman-Stanley polytopes. This is joint work with H. Nam, P.E. Harris, G. Dorpalen-Barry, S. Butler, J.L. Martin, C. Hettle, and Q. Liang.

• Speaker: Shi-Zhuo Looi, UC Berkeley
• Title: Asymptotics for odd- and even-dimensional waves
• Date: 09/28/2022
• Time: 4:10 PM - 5:00 PM
• Place: C304 Wells Hall
• Contact: Willie Wai-Yeung Wong (wongwil2@msu.edu)

In this talk, I will give a survey of recent and upcoming results on various linear, semilinear and quasilinear wave equations on a wide class of dynamical spacetimes in various even and odd spatial dimensions. These results include asymptotics for a wide range of nonlinearities. We also highlight a dichotomy in odd dimensions between stationary and nonstationary backgrounds and explain how the stationary backgrounds lead to a faster decay rate for waves. For many of these results, the spacetimes under consideration have only weak asymptotic flatness conditions and are allowed to be large perturbations of the Minkowski spacetime. We explain the dichotomy between even- and odd-dimensional wave behaviour and how we view this dichotomy as a generalisation of the contrast between the classical weak Huygens' principle and the classical strong Huygens' principle. Part of this work is joint with Mihai Tohaneanu and Jared Wunsch.

• Speaker: Peikai Qi, MSU
• Title: Hecke algebra and Atkin-Lehner-Li’s theory
• Date: 09/29/2022
• Time: 3:00 PM - 4:00 PM
• Place: C204A Wells Hall
• Contact: Peikai Qi (qipeikai@msu.edu)

We will use double closet to define Hecke algebra. And then we will have an review of Atkin-Lehner-Li’s theory without proof. If you miss the last seminar, it doesn’t matter. you can also understand most of this section.

• Speaker: Nam Le, Indiana University Bloomington
• Title: Hessian eigenvalues and hyperbolic polynomials
• Date: 09/29/2022
• Time: 4:10 PM - 5:00 PM
• Place: C304 Wells Hall
• Contact: Olga Turanova (turanova@msu.edu)

Hessian eigenvalues are natural nonlinear analogues of the classical Dirichlet eigenvalues. The Hessian eigenvalues and their corresponding eigenfunctions are expected to share many analytic and geometric properties (such as uniqueness, stability, max-min principle, global smoothness, Brunn-Minkowski inequality, etc) as their Dirichlet counterparts. In this talk, I will discuss these issues and some recent progresses in various geometric settings. The focus will be mostly on the case of the Monge-Ampere eigenfunctions and related degenerate equations. I will also explain the unexpected role of hyperbolic polynomials in our analysis. I will not assume any familiarity with these concepts.