Seminar information archive

Seminar information archive ~03/18Today's seminar 03/19 | Future seminars 03/20~

2024/03/14

Colloquium

14:30-17:00   Room #大講義室(auditorium) (Graduate School of Math. Sci. Bldg.)
If you do not belong to Graduate School of Mathematical Sciences, the University of Tokyo, please apply from the form at [Reference URL].
Toshiyasu Arai (Graduate School of Mathematical Sciences, The University of Tokyo) 14:30-15:30
Many years from now (JAPANESE)
[ Abstract ]
I have been studying proof theory since the 1980's. In this talk I will talk about what happened to me in these 40 years, and let me report the latest result on ordinal analysis.
[ Reference URL ]
https://forms.gle/m38f1KRi67ECuA7MA
Masahiro Yamamoto (Graduate School of Mathematical Sciences, The University of Tokyo) 16:00-17:00
Mathematics, which I eventually found that I like: from the viewpoint of some marginal areas (JAPANESE)
[ Abstract ]
Looking back on my experiences over 40 years, I have been convinced that I have been loving my own mathematics among others.

After all, I can sum up as that all my mathematics are concerned with the three topics: control theories, inverse problems and time-fractional partial differential equations. Some of these research fields has already developed to major topics, while others keep still minor interests.

When I started studies on inverse problems in 1980's, there were very few population of mathematicians as specialists in Japan. In particular, inverse problems did not call great attention of mathematicians and were understood as marginal mathematical topics in spite of practical significance and demands On the other hand, possibly available methodologies and ideas have been exploited and integrated gradually. As consequence, main research partners have been outside Japan.
I have been enjoying not only the research contents, but also such wider collaboration.

Aiming at non-meaningless reference for the youngers, and trying not to be too retrospective, I will describe how I have done in mathematics as well as my research contents.
[ Reference URL ]
https://forms.gle/m38f1KRi67ECuA7MA

Tokyo-Nagoya Algebra Seminar

10:30-12:00   Online
Arashi Sakai (Nagoya University)
Lattices of torsion classes in representation theory of finite groups (Japanese)
[ Reference URL ]
http://www.math.nagoya-u.ac.jp/~aaron.chan/TNAseminar.html

2024/03/13

Numerical Analysis Seminar

16:30-17:30   Online
David Sommer (Weierstrass Institute for Applied Analysis and Stochastics)
Approximating Langevin Monte Carlo with ResNet-like neural network architectures (English)
[ Abstract ]
We analyse a method to sample from a given target distribution by constructing a neural network which maps samples from a simple reference distribution, e.g. the standard normal, to samples from the target distribution. For this, we propose using a neural network architecture inspired by the Langevin Monte Carlo (LMC) algorithm. Based on LMC perturbation results, approximation rates of the proposed architecture for smooth, log-concave target distributions measured in the Wasserstein-2 distance are shown. The analysis heavily relies on the notion of sub-Gaussianity of the intermediate measures of the perturbed LMC process. In particular, we derive bounds on the growth of the intermediate variance proxies under different assumptions on the perturbations. Moreover, we propose an architecture similar to deep residual neural networks (ResNets) and derive expressivity results for approximating the sample to target distribution map.
[ Reference URL ]
https://sites.google.com/g.ecc.u-tokyo.ac.jp/utnas-bulletin-board/

Numerical Analysis Seminar

17:30-18:30   Online
Andreas Rathsfeld (Weierstrass Institute for Applied Analysis and Stochastics)
Analysis of the Scattering Matrix Algorithm (RCWA) for Diffraction by Periodic Surface Structures (English)
[ Abstract ]
The scattering matrix algorithm is a popular numerical method for the diffraction of optical waves by periodic surfaces. The computational domain is divided into horizontal slices and, by a clever recursion, an approximated operator, mapping incoming into outgoing waves, is obtained. Combining this with numerical schemes inside the slices, methods like RCWA and FMM have been designed.
The key for the analysis is the scattering problem with special radiation conditions for inhomogeneous cover materials. If the numerical scheme inside the slices is the FEM, then the scattering matrix algorithm is nothing else than a clever version of a domain decomposition method.
[ Reference URL ]
https://sites.google.com/g.ecc.u-tokyo.ac.jp/utnas-bulletin-board/

2024/03/12

Tuesday Seminar of Analysis

16:00-17:30   Room #123 (Graduate School of Math. Sci. Bldg.)
Kobe Marshall-Stevens (University College London)
On the generic regularity of min-max CMC hypersurfaces (English)
[ Abstract ]
Smooth constant mean curvature (CMC) hypersurfaces serve as effective tools to study the geometry and topology of Riemannian manifolds. In high dimensions however, one in general must account for their singular behaviour. I will discuss how such hypersurfaces are constructed via min-max techniques and some recent progress on their generic regularity, allowing for certain isolated singularities to be perturbed away.
[ Reference URL ]
https://forms.gle/7mqzgLqhtBuAovKB8

2024/03/11

FJ-LMI Seminar

13:30-14:30   Room #117 (Graduate School of Math. Sci. Bldg.)
Florian SALIN (Université de Lyon - 東北大学)
Fractional Nonlinear Diffusion Equation: Numerical Analysis and Large-time Behavior. (英語)
[ Abstract ]
This talk will discuss a fractional nonlinear diffusion equation on bounded domains. This equation arises by combining fractional (in space) diffusion, with a nonlinearity of porous medium or fast diffusion type. It is known that, in the porous medium case, the energy of the solutions to this equation decays algebraically, and in the fast diffusion case, solutions extinct in finite time. Based on these estimates, we will study the fine large-time asymptotic behavior of the solutions. In particular, we will show that the solutions approach separate variable solutions as the time converges to infinity in the porous medium case, or as it converges to the extinction time in the fast diffusion case. However, the extinction time is not known analytically, and to compute it, we will introduce a numerical scheme that satisfies the same decay estimates as the continuous equation.
[ Reference URL ]
https://fj-lmi.cnrs.fr/seminars/

2024/02/21

Number Theory Seminar

17:00-18:00   Room #117 (Graduate School of Math. Sci. Bldg.)
Jens Niklas Eberhardt (University of Bonn)
K-motives and Local Langlands (English)
[ Abstract ]
In this talk, we construct a geometric realisation of the category of representations of the affine Hecke algebra. For this, we introduce a formalism of K-theoretic sheaves (called K-motives) on stacks. The affine Hecke algebra arises from the K-theory of the Steinberg stack, and we explain how to “category” using K-motives.
Lastly, we briefly discuss the relation to the local Langlands program.

2024/02/13

Tuesday Seminar on Topology

17:00-18:30   Room #ハイブリッド開催/056 (Graduate School of Math. Sci. Bldg.)
Pre-registration required. See our seminar webpage.
Paul Norbury (The University of Melbourne)
Measures on the moduli space of curves and super volumes (ENGLISH)
[ Abstract ]
In this lecture I will define a family of finite measures on the moduli space of smooth curves with marked points. The measures are defined via a construction analogous to that of the Weil-Petersson metric using the extra data of a spin structure. In fact, the measures arise naturally out of the super Weil-Petersson metric defined over the moduli space of super curves. The total measure can be identified with the volume of the moduli space of super curves. It can be calculated in many examples, and conjecturally satisfies a recursion analogous to Mirzakhani's recursion relations between Weil-Petersson volumes of moduli spaces of hyperbolic surfaces. This conjecture has been verified in many cases, including the so-called Neveu-Schwarz case where it coincides with the recursion of Stanford and Witten. The general case produces deformations of the Neveu-Schwarz volume polynomials, satisfying the same Mirzakhani-like recursion relations.
[ Reference URL ]
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html

2024/02/08

Information Mathematics Seminar

16:50-18:35   Room #128 (Graduate School of Math. Sci. Bldg.)
Keita Kanno (QunaSys Inc.)
Current status of quantum computing and its applications (Japanese)
[ Abstract ]
In this seminar, current status and future prospects of quantum computing and its applications will be presented.

2024/02/05

Applied Analysis

16:00-17:30   Room #122 (Graduate School of Math. Sci. Bldg.)
Reinhard Farwig (Technische Universität Darmstadt)
Viscous Flow in Domains with Moving Boundaries - From Bounded to Unbounded Domains (English)
[ Abstract ]
https://drive.google.com/file/d/1dJJU1ybE-n8yn3LZTReTeH2UFX9wXQv9/view?usp=drive_link
[ Reference URL ]
https://forms.gle/xKPKu1uw9PeHEEck9

Tokyo Probability Seminar

17:00-18:30   Room #126 (Graduate School of Math. Sci. Bldg.)
Sunder Sethuraman (University of Arizona)
Atypical behaviors of a tagged particle in asymmetric simple exclusion (English)
[ Abstract ]
Informally, the one dimensional asymmetric simple exclusion process follows a collection of continuous time random walks on Z interacting as follows: When a clock rings, the particle jumps to the nearest right or left with probabilities p or q=1-p, if that location is unoccupied. If occupied, the jump is suppressed and clocks start again.

In this system, seen as a toy model of `traffic', the motion of a distinguished or `tagged' particle is of interest. Starting from a stationary state, we study the `typical' behavior of a tagged particle, conditioned to deviate to an `atypical' position at time Nt, for a t>0 fixed. In the course of results, an `upper tail' large deviation principle, in scale N, is established for the position of the tagged particle. Also, with respect to `lower tail' events, in the totally asymmetric version, a connection is made with a `nonentropy' solution of the associated hydrodynamic Burgers equation. This is work with S.R.S. Varadhan (arXiv:2311.0780).

2024/01/30

FJ-LMI Seminar

16:30-17:30   Room # (Graduate School of Math. Sci. Bldg.)
Danielle HILHORST (CNRS, Université de Paris-Saclay, France)
Convergence of solutions of a one-phase Stefan problem with Neumann boundary data to a self-similar profile (英語)
[ Abstract ]
We study a one-dimensional one-phase Stefan problem with a Neumann boundary condition on the fixed part of the boundary.
We construct a unique self-similar solution and show that for a large class of initial data, the solution of the time evolution problem
converges to this self-similar solution as time tends to infinity. Similar results were already obtained by Bouguezzi, Hilhorst,
Miyamoto, and Scheid in the case of Dirichlet data on the fixed boundary. However, they had to show that the space derivative
of the solution uniformly converges to its limit. Here, our proof requires less regularity, which should make our arguments easier
to adapt to different settings.

This is a joint work with Sabrina Roscani and Piotr Rybka.
[ Reference URL ]
https://fj-lmi.cnrs.fr/seminars/

Applied Analysis

16:30-17:30   Room #002 (Graduate School of Math. Sci. Bldg.)
Danielle Hilhorst (CNRS / Université de Paris-Saclay)
Convergence of solutions of a one-phase Stefan problem with Neumann boundary data to a self-similar profile. (English)
[ Abstract ]
We study a one-dimensional one-phase Stefan problem with a Neumann boundary condition on the fixed part of the boundary.
We construct a unique self-similar solution and show that for a large class of initial data, the solution of the time evolution problem converges to this self-similar solution as time tends to infinity. Similar results were already obtained by Bouguezzi, Hilhorst, Miyamoto, and Scheid in the case of Dirichlet data on the fixed boundary. However, they had to show that the space derivative of the solution uniformly converges to its limit. Here, our proof requires less regularity, which should make our arguments easier to adapt to different settings.
This is a joint work with Sabrina Roscani and Piotr Rybka.

2024/01/26

thesis presentations

9:15-10:30   Room #118 (Graduate School of Math. Sci. Bldg.)
YAMAGUCHI Tatsuki (Graduate School of Mathematical Sciences University of Tokyo)
Studies on F-singularities in equal characteristic zero via ultraproducts
(超積を用いた等標数0におけるF-特異点の研究)

thesis presentations

9:15-10:30   Room #128 (Graduate School of Math. Sci. Bldg.)
INOUE Daisuke (Graduate School of Mathematical Sciences University of Tokyo)
Numerical Methods for Nonlinear Partial Differential Equations Arising from Large-Scale Multi-Agent Control Problems
(大規模​マルチエージェント制御問題に現れる非線形偏微分方程式の数値計算)

thesis presentations

11:00-12:15   Room #118 (Graduate School of Math. Sci. Bldg.)
SHIMADA Ryosuke (Graduate School of Mathematical Sciences University of Tokyo)
Geometric Structure of Affine Deligne-Lusztig Varieties for GLn
(GLnのアファインDeligne-Lusztig多様体の幾何構造)

thesis presentations

11:00-12:15   Room #128 (Graduate School of Math. Sci. Bldg.)
ETO Tokuhiro (Graduate School of Mathematical Sciences University of Tokyo)
Numerical Analysis for Geometric Evolution Equations
(幾何学的発展方程式に対する数値解析)

thesis presentations

13:00-14:15   Room #126 (Graduate School of Math. Sci. Bldg.)
OIKAWA Mizuki (Graduate School of Mathematical Sciences University of Tokyo)
Equivariant α-induction Frobenius algebras and related constructions of tensor categories
(同変α-誘導フロベニウス代数と関連するテンソル圏の構成)

thesis presentations

14:45-16:00   Room #118 (Graduate School of Math. Sci. Bldg.)
KOIZUMI Junnosuke (Graduate School of Mathematical Sciences University of Tokyo)
Study of motives with modulus using Q-divisors
(モジュラス付きモチーフのQ因子を用いた研究)

thesis presentations

14:45-16:00   Room #122 (Graduate School of Math. Sci. Bldg.)
MIYAZAWA Jin (Graduate School of Mathematical Sciences University of Tokyo)
Real Seiberg-Witten theory and its applications to surfaces in 4-manifolds
(実Seiberg-Witten理論とその4次元多様体に埋め込まれた曲面への応用)

thesis presentations

14:45-16:00   Room #126 (Graduate School of Math. Sci. Bldg.)
HASHIBA Yasuhito (Graduate School of Mathematical Sciences University of Tokyo)
On the structure of crossed product von Neumann algebras
(接合積von Neumann環の構造について)

thesis presentations

14:45-16:00   Room #128 (Graduate School of Math. Sci. Bldg.)
YAMAGISHI Hayate ( )
Asymptotic expansion of estimators related to diffusion processes driven by fractional Brownian motion
(非整数ブラウン運動によって駆動される拡散過程に関わる推定量の漸近展開)

2024/01/25

Information Mathematics Seminar

16:50-18:35   Room #056 (Graduate School of Math. Sci. Bldg.)
Yasunari Suzuki (NTT)
Design and control of fault-tolerant quantum computer (Japanese)
[ Abstract ]
To demonstrate quantum computational advantage, we need quantum error-correction technology to reduce effective error rates to a small value. In this talk, we explain methods to fault-tolerantly control encoded logical information and methods to translate practical algorithms to basic operations.

thesis presentations

9:15-10:30   Room #122 (Graduate School of Math. Sci. Bldg.)
TAKANO Akihiro (Graduate School of Mathematical Sciences University of Tokyo)
Studies on knot theory using braid groups and Thompson’s group
(組み紐群とトンプソン群を用いた結び目理論の研究)

thesis presentations

9:15-10:30   Room #128 (Graduate School of Math. Sci. Bldg.)
HIGASHI Kohei (Graduate School of Mathematical Sciences University of Tokyo)
Fuzzy cellular automaton and systems with singular integrals and their applications
(ファジーセルオートマトンおよび特異積分をもつシステムの数理とその応用)

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