Fall 2022 analysis seminar

The 2022-2023 Analysis Seminar will be organized by Shaoming Guo. The regular time and place for the Seminar will be Tuesdays at 4:00 p.m. in Van Vleck B139 (in some cases the seminar may be scheduled at different time to accommodate speakers). If you would like to subscribe to the Analysis seminar list, send a blank email to analysis+join (at) g-groups (dot) wisc (dot) edu. If you are from an institution different than UW-Madison, please send as well as an additional email to Shaoming. If you'd like to suggest speakers for the spring semester please contact Shaoming.

All talks will be in-person unless otherwise specified.

Analysis Seminar Schedule

date	speaker	institution	title	host(s)
08.23	Gustavo Garrigós	University of Murcia	Approximation by N-term trigonometric polynomials and greedy algorithms	Andreas Seeger
08.30	Simon Myerson	Warwick	Forms of the Circle Method	Shaoming Guo
09.13 (first week of semester)	Zane Li	UW Madison	A decoupling interpretation of an old argument for Vinogradov's Mean Value Theorem	Analysis group
09.16 (Friday, 1:20-2:10, Room B139)	Franky Li	UW Madison	Affine restriction estimates for surfaces in R^3 via decoupling	Analysis group
09.20 (Joint with PDE and Geometric Analysis seminar)	Andrej Zlatoš	UCSD	Homogenization in front propagation models	Hung Tran
09.23 Friday, Colloquium	Pablo Shmerkin	UBC	Incidences and line counting: from the discrete to the fractal setting	Shaoming Guo and Andreas Seeger
09.23-09.25	RTG workshop in Harmonic Analysis			Shaoming Guo and Andreas Seeger
09.27 (online, special time, 3-4pm)	Michael Magee	Durham	The maximal spectral gap of a hyperbolic surface	Simon Marshall
10.04	Philip Gressman	UPenn	Sublevel Set Estimates in Higher Dimensions: Symmetry and Uniformity	Shaoming Guo
10.11	Detlef Müller	CAU Kiel	Maximal averages along hypersurfaces: a geometric conjecture and further progress for 2-surfaces	Betsy Stovall and Andreas Seeger
10.14 (1:20 PM Friday, 901 Van Vleck. Joint with Geometry & Topology Seminar)	Min Ru	U of Houston	The K-stability and Nevanlinna/Diophantine theory	Xianghong Gong
10.18	Madelyne M. Brown	UNC	Fourier coefficients of restricted eigenfunctions	Betsy Stovall
10.24 (Monday, B135)	Milivoje Lukic	Rice	An approach to universality using Weyl m-functions	Sergey Denisov
11.01	Ziming Shi	Rutgers	Sobolev Differentiability Properties of the Modulus of Real Analytic Functions	Xianghong Gong
11.04 (Friday, 1:20-2:10, in room tbd)	Sarah Tammen	MIT		Betsy Stovall
11.08	Robert Fraser	Wichita State University	Explicit Salem Sets in $\mathbb{R}^n$	Andreas Seeger
11.15	Brian Cook	Virginia Tech	Title	Brian Street
11.22	Thanksgiving
11.29	Jaume de Dios Pont	UCLA	Title	Betsy Stovall
12.06	Shengwen Gan	MIT	Title	Shaoming Guo and Andreas Seeger
12.13	Óscar Domínguez	Universidad Complutense Madrid and University of Lyons	Title	Andreas Seeger and Brian Street
Spring 2023
3.14	Liding Yao	Ohio State		Brian Street

Spring 2023 Analysis Seminar

Abstracts

Gustavo Garrigós

Title: Approximation by N-term trigonometric polynomials and greedy algorithms

Link to Abstract: [1]

Simon Myerson

Title: Forms of the circle method

Abstract: The circle method is an analytic proof strategy, typically used in number theory when one wants to estimate the number of integer lattice points in some interesting set. Traditionally the first step is to evaluate the innocent integral $ \int_0^1 e^{2 \pi i t n} dt $ to give 1 if $ n = 0 $ and 0 if $ n $ is any other integer. Since Heath-Brown’s delta-method in the 90s this simplest step has been embellished with carefully constructed partitions of unity. In this informal discussion I will interpret these as different versions of the circle method and suggest how to understand their relative advantages.

Andrej Zlatos

Title: Homogenization in front propagation models

Abstract: Homogenization is a general principle that the dynamics of physical processes occurring in periodic or random environments often become effectively homogeneous in the long-time-large-scale limit. I will presents results showing that homogenization occurs for reaction-diffusion equations with both time-periodic-spatially-random and space-time-random KPP reactions and coefficients. These results rely on two crucial new tools: virtual linearity of KPP reaction-diffusion dynamics and a non-autonomous versions of Kingman’s subadditive ergodic theorem.

Zane Li

Title: A decoupling interpretation of an old argument for Vinogradov's Mean Value Theorem

Abstract: There are two proofs of Vinogradov's Mean Value Theorem (VMVT), the harmonic analysis decoupling proof by Bourgain, Demeter, and Guth from 2015 and the number theoretic efficient congruencing proof by Wooley from 2017. While there has been recent work illustrating the relation between these two methods, VMVT has been around since 1935. It is then natural to ask: What does old partial progress on VMVT look like in harmonic analysis language? How similar or different does it look from current decoupling proofs? We talk about a refinement of a 1973 argument of Karatsuba that showed partial progress towards VMVT and interpret this in decoupling language. This yields an argument that only uses rather simple geometry of the moment curve. This is joint work with Brian Cook, Kevin Hughes, Olivier Robert, Akshat Mudgal, and Po-Lam Yung.

Jianhui Li

Title: Affine restriction estimates for surfaces in \mathbb{R}^3 via decoupling

Abstract: We will discuss some L^2 restriction estimates for smooth compact surfaces in \mathbb{R}^3 with weights that respect affine transformations. The key ingredient is a decoupling inequality. The results are also uniform for polynomial surfaces of bounded degrees and coefficients. Part of the work is joint with Tongou Yang.

Pablo Shmerkin

Title: Incidences and line counting: from the discrete to the fractal setting

Abstract: How many lines are spanned by a set of planar points?. If the points are collinear, then the answer is clearly "one". If they are not collinear, however, several different answers exist when sets are finite and "how many" is measured by cardinality. I will discuss a bit of the history of this problem and present a recent extension to the continuum setting, obtained in collaboration with T. Orponen and H. Wang. No specialized background will be assumed.

Michael Magee

Title: The maximal spectral gap of a hyperbolic surface

Abstract: A hyperbolic surface is a surface with metric of constant curvature -1. The spectral gap between the first two eigenvalues of the Laplacian on a closed hyperbolic surface contains a good deal of information about the surface, including its connectivity, dynamical properties of its geodesic flow, and error terms in geodesic counting problems. For arithmetic hyperbolic surfaces the spectral gap is also the subject of one of the biggest open problems in automorphic forms: Selberg's eigenvalue conjecture.

A conjecture of Buser from the 1980s stated that there exists a sequence of closed hyperbolic surfaces with genera tending to infinity and spectral gap tending to 1/4. (The value 1/4 here is the asymptotically optimal one.) We proved that such a sequence does exist. I'll discuss the very interesting background of this problem in detail as well as some ideas of the proof.

This is joint work with Will Hide.

Philip Gressman

Title: Sublevel Set Estimates in Higher Dimensions: Symmetry and Uniformity

Abstract: Using even simple derivative bounds, it is possible to understand the behavior of smooth functions of a single real variable in very precise ways. In contrast, when one moves to dimensions 2 and higher, current best approaches fail to yield the same kind of sharp, uniform inequalities that are relatively easy to obtain in 1D. I will discuss a number of related problems which attempt to illuminate some of the reasons for this discrepancy and to formulate new ways of working in higher dimensions to recover some of the robustness that is available in 1D. Of particular interest will be sublevel sets and uniform estimates for integrals of the sort found in the theory of critical integrability exponents. One main result will show how machinery developed for the study of affine Hausdorff measure can be used to build nonlinear differential operators whose nonvanishing implies uniform sublevel set estimates and bounds for related integrals.

Detlef Müller

Tirlw: Maximal averages along hypersurfaces: a ``geometric conjecture and further progress for 2-surfaces.

Link to Abstract: [2]

Min Ru

Title: The K-stability and Nevanlinna/Diophantine theory

Abstract: In the recent paper with P. Vojta, we introduced the so-called beta-constant, and used it to extend the Cartan's Second Main Theorem in Nevanlinna theory and Schmidt's subspace theorem in Diophantine approximation. It turns out the beta-constant is also used in the algebro-geometric stability criterion in the Fano's case. In this talk, I'll describe and explore the somewhat mysterious connection. The talk is based on the recent joint paper with Yan He entitled "The stability threshold and Diophantine approximation", Proc. AMS, 2022.

Madelyne M. Brown

Title: Fourier coefficients of restricted eigenfunctions

Abstract: We will discuss the growth of Laplace eigenfunctions on a compact manifold when restricted to a submanifold. We analyze the behavior of the restricted eigenfunctions by studying their Fourier coefficients with respect to an arbitrary orthonormal basis for the submanifold. We give an explicit bound on these coefficients depending on how the defect measures for the two collections of functions, the eigenfunctions and the basis, relate.

Milivoje Lukic

Title: An approach to universality using Weyl m-functions

Abstract:

I will describe an approach to universality limits for orthogonal polynomials on the real line which is completely local and uses only the boundary behavior of the Weyl $m$-function at the point. We show that bulk universality of the Christoffel--Darboux kernel holds for any point where the imaginary part of the $m$-function has a positive finite nontangential limit. This approach is based on studying a matrix version of the Christoffel--Darboux kernel and the realization that bulk universality for this kernel at a point is equivalent to the fact that the corresponding $m$-function has normal limits at the same point. Our approach automatically applies to other self-adjoint systems with $2\times 2$ transfer matrices such as continuum Schr\"odinger and Dirac operators. We also obtain analogous results for orthogonal polynomials on the unit circle. This is joint work with Benjamin Eichinger and Brian Simanek.

Ziming Shi

Title: Sobolev Differentiability Properties of the Logarithmic Modulus of Real Analytic Functions

Abstract: Let $f$ be the germ of a real analytic function at the origin in $\mathbb{R}^n $ for $n \geq 2$, and suppose the codimension of the zero set of $f$ at $\mathbf{0}$ is at least $2$. We show that $\log |f|$ is $W^{1,1}_{\operatorname{loc}}$ near $\mathbf{0}$. In particular, this implies the differential inequality $|\nabla f |\leq V |f|$ holds with $V \in L^1_{\operatorname{loc}}$. As an application, we derive an inequality relating the {\L}ojasiewicz exponent and the singularity exponent for such functions. This is joint work with Ruixiang Zhang.

Robert Fraser

Title: Explicit Salem Sets in $\mathbb{R}^n$

Link to Abstract: [https://people.math.wisc.edu/~seeger/rfraser22-Abstract.pdf}

Name

Title:

Abstract

Link to the analysis seminar in spring 2023

Links to previous analysis seminars