過去の記録

過去の記録 ~07/24本日 07/25 | 今後の予定 07/26~

離散数理モデリングセミナー

13:30-15:00   数理科学研究科棟(駒場) 126号室
Jaume Alonso 氏 (Technische Universität Berlin)
Discrete Painlevé equations and pencils of quadrics in 3D (English)
[ 講演概要 ]
In this talk we propose a new geometric interpretation of discrete Painlevé equations. From this point of view, the equations are birational transformations of $\mathbb{P}^3$ that preserve a pencil of quadrics and map each quadric of the pencil to a different one, according to a Möbius transformation of the pencil parameter. This allows for a classification of discrete Painlevé equations based on the classification of pencils of quadrics in $\mathbb{P}^3$. In this scheme, discrete Painlevé equations are obtained as deformations of the 3D QRT maps introduced in the previous talk, which consist of the composition of two involutions along the generators of the quadrics of a pencil of quadrics until they meet a second pencil. The deformation is then a birational (often linear) transformation in $\mathbb{P}^3$ under which the pencil remains invariant, but the individual quadrics do not.

This is a joint work with Yuri Suris and Kangning Wei.

2024年04月16日(火)

トポロジー火曜セミナー

17:00-18:00   オンライン開催
参加を希望される場合は、セミナーのホームページから参加登録を行って下さい。
軽尾 浩晃 氏 (学習院大学)
パンツ分解によるスケイン代数と量子トーラスの関係 (JAPANESE)
[ 講演概要 ]
近年, スケイン代数やその一般化の代数構造の理解において, 曲面の理想3角形分割と分裂写像を用いて量子トーラスへの埋め込みが構成されている. しかし, 閉曲面のスケイン代数や穴あき曲面のRoger--Yangスケイン代数に対してはこの分裂写像は上手く振る舞わず, これらの代数構造を調べるには別の手法が必要である. 本講演では, 上記の代数に対して曲面のパンツ分解を用いてフィルトレーションを定め, これらの随伴次数付き代数が量子トーラスへ埋め込めることを紹介する. この帰結として, Roger--Yangスケイン代数は飾り付きタイヒミュラー空間の量子化であることが従う. 本講演は, Wade Bloomquist (Morningside University), Thang Le (Georgia Institute of Technology)との共同研究に基づく.
[ 参考URL ]
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html

作用素環セミナー

16:45-18:15   数理科学研究科棟(駒場) 126号室
Jean Roydor 氏 (Sorbonne Université)
Perturbations of von Neumann algebras
[ 参考URL ]
https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm

2024年04月15日(月)

東京確率論セミナー

16:00-17:30   数理科学研究科棟(駒場) 126号室
15:15〜 2階のコモンルームでTea timeを行いますので、ぜひそちらにもご参加ください。
綾 朝弘 氏 (京都大学)
Quantitative stochastic homogenization of elliptic equations with unbounded coefficients (日本語)
[ 講演概要 ]
確率的均質化(Stochastic Homogenization)の分野において,解の収束を定量的に評価する研究が近年盛んに行われている.しかし従来の研究の対象は方程式のランダム係数が一様楕円性を持つ標本空間であり,非有界な係数を含む方程式での確率的均質化の定量的な結果は少ない.本講演ではsubadditive argument を非有界係数の場合に拡張することにより,非有界な係数を含む楕円型PDEの解の収束の速さを評価する.時間に余裕があれば関連する問題について紹介する.

複素解析幾何セミナー

10:30-12:00   数理科学研究科棟(駒場) 128号室
竹内 有哉 氏 (筑波大学)
Kohn-Rossi cohomology of spherical CR manifolds (Japanese)
[ 講演概要 ]
The Kohn-Rossi cohomology is a CR analog of the Dolbeault cohomology and is one of fundamental invariants in CR geometry. In this talk, we prove some vanishing theorems for the Kohn-Rossi cohomology of some spherical CR manifolds. To this end, we use a canonical contact form defined via the Patterson-Sullivan measure and Weitzenböck-type formulae.
[ 参考URL ]
https://forms.gle/gTP8qNZwPyQyxjTj8

2024年04月11日(木)

応用解析セミナー

16:00-17:30   数理科学研究科棟(駒場) 126号室
対面・オンラインハイブリッド開催
Jan Haskovec 氏 (KAUST, Saudi Arabia)
Non-Markovian models of collective motion (English)
[ 講演概要 ]
I will give an overview of recent results for models of collective behavior governed by functional differential equations with non-Markovian structure. The talk will focus on models of interacting agents with applications in biology (flocking, swarming), social sciences (opinion formation) and engineering (swarm robotics), where latency (delay) plays a significant role. I will characterize two main sources of delay - inter-agent communications ("transmission delay") and information processing ("reaction delay") - and discuss their impacts on the group dynamics. I will give an overview of analytical methods for studying the asymptotic behavior of the models in question and their mean-field limits. In particular, I will show that the transmission vs. reaction delay leads to fundamentally different mathematical structures and requires appropriate choice of analytical tools. Finally, motivated by situations where finite speed of information propagation is significant, I will introduce an interesting class of problems where the delay depends nontrivially and nonlinearly on the state of the system, and discuss the available analytical results and open problems here.
[ 参考URL ]
https://forms.gle/5cZ4WzqBjhsXrxgU6

2024年04月10日(水)

日仏数学拠点FJ-LMIセミナー

16:00-17:00   数理科学研究科棟(駒場) 056号室
Séverin PHILIP 氏 (京都大学 数理解析研究所, RIMS, Kyoto University)
Galois outer representation and the problem of Oda
(英語)
[ 講演概要 ]
Oda’s problem stems from considering the pro-l outer Galois actions on the moduli spaces of hyperbolic curves. These actions come from a generalization by Oda of the standard étale homotopy exact sequence for algebraic varieties over the rationals. We will introduce these geometric Galois actions and present some of the mathematics that they have stimulated over the past 30 years along with the classical problem of Oda. In the second and last part of this talk, we will see how a cyclic special loci version of this problem can be formulated and resolved in the case of simple cyclic groups using the maximal degeneration method of Ihara and Nakamura adapted to this setting.
[ 参考URL ]
https://fj-lmi.cnrs.fr/seminars/

統計数学セミナー

13:30-14:40   数理科学研究科棟(駒場) 126号室
ハイブリッド形式
Ivan Nourdin 氏 (University of Luxembourg)
Limit theorems for additive functionals of stationary Gaussian fields (English)
[ 講演概要 ]
In this talk, we will investigate central and non-central limit theorems for additive functionals of stationary Gaussian fields. Our main tool will be the Malliavin-Stein approach. Based on joint works with Nikolai Leonenko, Leonardo Maini and Francesca Pistolato.
[ 参考URL ]
https://forms.gle/uMKm3gVquLpYaVdc6

離散数理モデリングセミナー

13:30-15:00   数理科学研究科棟(駒場) 056号室
セミナー室変更:470セミナー室→056セミナー室
Jaume Alonso 氏 (Technische Universität Berlin)
Integrable birational maps and a generalisation of QRT to 3D (English)
[ 講演概要 ]
When completely integrable Hamiltonian systems are discretised, the resulting discrete-time systems are often no longer integrable themselves. This is the so-called problem of integrable discretisation. Two known exceptions to this situation in 3D are the Kahan-Hirota-Kimura discretisations of the Euler top and the Zhukovski-Volterra gyrostat with one non-zero linear parameter β, both birational maps of degree 3. The integrals of these systems define pencils of quadrics. By analysing the geometry of these pencils, we develop a framework that generalises QRT maps and QRT roots to 3D, which allows us to create new integrable maps as a composition of two involutions. We show that under certain geometric conditions, the new maps become of degree 3. We use these results to create new families of discrete integrable maps and we solve the problem of integrability of the Zhukovski-Volterra gyrostat with two β’s.

This is a joint work with Yuri Suris and Kangning Wei.

2024年04月09日(火)

トポロジー火曜セミナー

17:00-18:30   数理科学研究科棟(駒場) ハイブリッド開催/056号室
対面参加、オンライン参加のいずれの場合もセミナーのホームページから参加登録を行って下さい。
本多 正平 氏 (東京大学大学院数理科学研究科)
位相的安定性定理とグロモフ・ハウスドルフ収束 (JAPANESE)
[ 講演概要 ]
グロモフ・ハウスドルフ距離はコンパクト距離空間の同型類全体からなるモジュライ空間に距離構造を与える.そのモジュライ空間に定まる位相はとても弱いので,他の幾何学の枠組みで現れるモジュライ空間(例えばK3など)をコンパクト化したいときに役立つことがある.グロモフ・ハウスドルフ距離に関する基本的な問いの1つに「与えられた2つのコンパクト距離空間X,Yの間のグロモフ・ハウスドルフ距離が小さいときに,XとYの位相について何がいえるか」というものがある.リッチ曲率のコントロールのもとで,この問いに関して決定的な結果が90年代後半にCheegerとColdingによって得られた.本講演ではその結果をシャープな形にまで改良し,一般化する.そのための技術的なキーワードは「モジュライのコンパクト性」と「ほとんど線形増大度を持つ調和関数に対するリュービル型の定理」である.以上は東北大学のYuanlin Peng氏との共同研究である.また時間があればこの流れに沿った,調和写像と平坦トーラスへの概剛性との新しい関係についてもお話したい.こちらはChristian Ketterer (University of Freiburg),Ilaria Mondello (Université de Paris Est Créteil),Chiara Rigoni (University of Vienna)およびRaquel Perales (CIMAT)との共同研究である.
[ 参考URL ]
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html

作用素環セミナー

16:45-18:15   数理科学研究科棟(駒場) 126号室
谷本溶 氏 (Univ Rome, Tor Vergata)
Towards lattice construction of quantum field theories
[ 参考URL ]
https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm

2024年03月21日(木)

応用解析セミナー

16:00-17:30   数理科学研究科棟(駒場) 126号室
Mostafa Fazly 氏 (University of Texas at San Antonio)
Symmetry Results for Nonlinear PDEs (English)
[ 講演概要 ]
The study of qualitative behavior of solutions of Partial Differential Equations (PDEs) started roughly in mid-18th century. Since then scientists and mathematicians from different fields have put in a great effort to expand the theory of nonlinear PDEs. PDEs can be divided into two kinds: (a) the linear ones, which are relatively easy to analyze and can often be solved completely, and (b) the nonlinear ones, which are much harder to analyze and can almost never be solved completely.
We begin this talk by an introduction on foundational ideas behind the De Giorgi’s conjecture (1978) for the Allen-Cahn equation that is inspired by the Bernstein’s problem (1910). This conjecture brings together three groups of mathematicians: (a) a group specializing in nonlinear partial differential equations, (b) a group in differential geometry, and more specially on minimal surfaces and constant mean curvature surfaces, and (c) a group in mathematical physics on phase transitions. We then present natural generalizations and counterparts of the problem. These generalizations lead us to introduce certain novel concepts, and we illustrate why these novel concepts seem to be the right concepts in the context and how they can be used to study particular systems and models arising in Sciences. We give a survey of recent results.

2024年03月14日(木)

談話会・数理科学講演会

14:30-17:00   数理科学研究科棟(駒場) 大講義室(auditorium)号室
数理科学研究科所属以外の方は、[参考URL]から参加登録をお願いいたします。
新井 敏康 氏 (東京大学 大学院数理科学研究科) 14:30-15:30
40年くらい (JAPANESE)
[ 講演概要 ]
1980年代から証明論を研究してきました。この講演ではこの40年くらいの間に私に起きたことと順序数解析に関する最新の結果をお話しします。
[ 参考URL ]
https://forms.gle/m38f1KRi67ECuA7MA
山本 昌宏 氏 (東京大学 大学院数理科学研究科) 16:00-17:00
結局、好きだった数学:外縁部を歩んで (JAPANESE)
[ 講演概要 ]
40年余りたってから、今から振り返ってみると、異分野連携や運営業務にも携わってきたなかで結局、自分の数学が大好きだったと思いいたりました。自分の数学は、制御理論、逆問題、非整数階偏微分方程式の3つで尽くされます。これらは、現在では研究が盛んな分野に発展していたり、依然としてマイナーな部分もありますが、私が、たとえば逆問題をやり始めた頃は我が国では研究者人口が少なかったです。その頃は(今でもそうかもしれません)、これらの分野は、華々しい注目を浴びてはおらず数学研究の外縁部に位置していましたが、基礎として使いうる発想や方法論が辛抱強く蓄積されていた時期でした。

そのような状況にひかれて研究者としての歩みを始めました。研究活動の状況もあって、海外との研究者との共同研究が最初から大半を占めました。このような経過は、第3者の評価はともかくとして、自分に大きな楽しみを恵んでくれました。

この講演では、自分の数学の内容にふれつつ、研究の進め方などにも関連させて、回顧的になりすぎないようにお話しをしたいと思います。
[ 参考URL ]
https://forms.gle/m38f1KRi67ECuA7MA

東京名古屋代数セミナー

10:30-12:00   オンライン開催
酒井 嵐士 氏 (名古屋大学)
Lattices of torsion classes in representation theory of finite groups (Japanese)
[ 講演概要 ]
多元環の表現論においてtorsion classは古くから重要な部分圏の1つである。特にtorsion classの包含関係から得られるtorsion classの束は近年盛んに研究されており、wide intervalやbrick labellingはさまざまな良い性質が知られている。本講演では有限群の表現論においてtorsion classの束を観察する。具体的には有限群とその正規部分群の群環上の有限生成加群の圏においてtorsion classの束をそれぞれ考え、表現の誘導と制限がこれらの間に良い対応を誘導することを紹介する。また小塩-小境による台tau傾加群と誘導関手に関する結果、有限群の表現論における基本的な結果であるCliffordの定理が上記の良い対応とどのように関連するかを説明する。本講演は東京理科大学の小境雄太氏との共同研究(arXiv:2312.07299)に基づく。
[ 参考URL ]
http://www.math.nagoya-u.ac.jp/~aaron.chan/TNAseminar.html

2024年03月13日(水)

数値解析セミナー

16:30-17:30   オンライン開催
David Sommer 氏 (Weierstrass Institute for Applied Analysis and Stochastics)
Approximating Langevin Monte Carlo with ResNet-like neural network architectures (English)
[ 講演概要 ]
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.
[ 参考URL ]
https://sites.google.com/g.ecc.u-tokyo.ac.jp/utnas-bulletin-board/

数値解析セミナー

17:30-18:30   オンライン開催
Andreas Rathsfeld 氏 (Weierstrass Institute for Applied Analysis and Stochastics)
Analysis of the Scattering Matrix Algorithm (RCWA) for Diffraction by Periodic Surface Structures (English)
[ 講演概要 ]
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.
[ 参考URL ]
https://sites.google.com/g.ecc.u-tokyo.ac.jp/utnas-bulletin-board/

2024年03月12日(火)

解析学火曜セミナー

16:00-17:30   数理科学研究科棟(駒場) 123号室
対面・オンラインハイブリッド開催,通常とは場所が異なります
Kobe Marshall-Stevens 氏 (University College London)
On the generic regularity of min-max CMC hypersurfaces (English)
[ 講演概要 ]
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.
[ 参考URL ]
https://forms.gle/7mqzgLqhtBuAovKB8

2024年03月11日(月)

日仏数学拠点FJ-LMIセミナー

13:30-14:30   数理科学研究科棟(駒場) 117号室
Florian SALIN 氏 (Université de Lyon - Tohoku University)
Fractional Nonlinear Diffusion Equation: Numerical Analysis and Large-time Behavior. (英語)
[ 講演概要 ]
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.
[ 参考URL ]
https://fj-lmi.cnrs.fr/seminars/

2024年02月21日(水)

代数学コロキウム

17:00-18:00   数理科学研究科棟(駒場) 117号室
Jens Niklas Eberhardt 氏 (University of Bonn)
K-motives and Local Langlands (English)
[ 講演概要 ]
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年02月13日(火)

トポロジー火曜セミナー

17:00-18:30   数理科学研究科棟(駒場) ハイブリッド開催/056号室
対面参加、オンライン参加のいずれの場合もセミナーのホームページから参加登録を行って下さい。
Paul Norbury 氏 (The University of Melbourne)
Measures on the moduli space of curves and super volumes (ENGLISH)
[ 講演概要 ]
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.
[ 参考URL ]
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html

2024年02月08日(木)

情報数学セミナー

16:50-18:35   数理科学研究科棟(駒場) 128号室
菅野 恵太 氏 (株式会社QunaSys)
量子コンピュータとその応用の現状 (Japanese)
[ 講演概要 ]
量子コンピュータは近年急速な発達を遂げている一方、未だ本格的な産業応用には至っていない。本講演では、量子コンピュータ開発の現状と展望を、産業応用を目指して量子アルゴリズム研究開発を行うベンチャー企業の視点から紹介する。

2024年02月05日(月)

応用解析セミナー

16:00-17:30   数理科学研究科棟(駒場) 122号室
対面・オンラインハイブリッド開催(通常と開催曜日・会場が異なりますのでご注意ください)
Reinhard Farwig 氏 (Technische Universität Darmstadt)
Viscous Flow in Domains with Moving Boundaries - From Bounded to Unbounded Domains (English)
[ 講演概要 ]
以下のPDFファイルをご参照ください:
https://drive.google.com/file/d/1dJJU1ybE-n8yn3LZTReTeH2UFX9wXQv9/view?usp=drive_link
[ 参考URL ]
https://forms.gle/xKPKu1uw9PeHEEck9

東京確率論セミナー

17:00-18:30   数理科学研究科棟(駒場) 126号室
16:15から2階のコモンルームでTea timeを行いますので、ぜひそちらにもご参加ください。
Sunder Sethuraman 氏 (University of Arizona)
Atypical behaviors of a tagged particle in asymmetric simple exclusion (English)
[ 講演概要 ]
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年01月30日(火)

日仏数学拠点FJ-LMIセミナー

16:30-17:30   数理科学研究科棟(駒場) 号室
Danielle HILHORST 氏 (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)
[ 講演概要 ]
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.
[ 参考URL ]
https://fj-lmi.cnrs.fr/seminars/

応用解析セミナー

16:30-17:30   数理科学研究科棟(駒場) 002号室
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Danielle Hilhorst 氏 (CNRS / Université de Paris-Saclay)
Convergence of solutions of a one-phase Stefan problem with Neumann boundary data to a self-similar profile. (English)
[ 講演概要 ]
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.

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