## 過去の記録

### 2020年05月28日(木)

#### 作用素環セミナー

16:45-18:15   オンライン開催

Index theorem of lattice Wilson-Dirac operators and almost-commuting matrices (English)
[ 参考URL ]
https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm

### 2020年05月27日(水)

#### 代数学コロキウム

17:30-18:30   オンライン開催

Shintani generating class and the p-adic polylogarithm for totally real fields (ENGLISH)
[ 講演概要 ]
In this talk, we will give a new interpretation of Shintani's work concerning the generating function of nonpositive values of Hecke $L$-functions for totally real fields. In particular, we will construct a canonical class, which we call the Shintani generating class, in the cohomology of a certain quotient stack of an infinite direct sum of algebraic tori associated with a fixed totally real field. Using our observation that cohomology classes, not functions, play an important role in the higher dimensional case, we proceed to newly define the p-adic polylogarithm function in this case, and investigate its relation to the special value of p-adic Hecke $L$-functions. Some observations concerning the quotient stack will also be discussed. This is a joint work with Kei Hagihara, Kazuki Yamada, and Shuji Yamamoto.
[ 参考URL ]
https://www.ms.u-tokyo.ac.jp/~t-saito/todai_IHES.html

### 2020年05月25日(月)

#### 複素解析幾何セミナー

10:30-12:00   オンライン開催

Cheng-Yau計量の特性形式とCR不変量
[ 講演概要 ]
Cheng-Yau計量は強擬凸領域上の双正則不変な完備Kähler-Einstein計量であり, その曲率の漸近挙動は境界のCR幾何によって記述される. この講演では, Cheng-Yau計量の特性形式の積分をrenormalizeすることによって境界の大域的CR不変量の族が得られることを説明する. また, Case-Goverによって導入されたI-prime曲率を一般化することで, CR多様体の高次の特性類の消滅から積分のCR不変性が従う曲率量を定義し, この曲率の積分が上記の不変量の族に現れることを示す.
[ 参考URL ]
https://forms.gle/vSFPoVR6ugrkTGhX7

### 2020年05月21日(木)

#### 情報数学セミナー

16:50-18:35   オンライン開催

コンピュータの誕生から演算速度のさらなる高速化へ (Japanese)
[ 講演概要 ]
URL
[学内用] https://bit.ly/2zCBj8x (g.ecc.u-tokyo.ac.jpアカウントでアクセスできます)

今日、高精細画像や情報処理の多様化に伴い、コンピュータの処理対象のデー
タ量の増大、処理の高度化に伴い、計算アルゴリズムが益々複雑化している。
また、高速化の要求に対する解決方法として並列計算と量子計算が、ホットな

と共にどこへ向かうのかを概観する。
[ 参考URL ]

#### 作用素環セミナー

16:45-18:15   オンライン開催

Partition functions as $C^*$-dynamical invariants and actions of congruence monoids (English)

### 2020年05月18日(月)

#### 複素解析幾何セミナー

10:30-12:00   オンライン開催

Higgs bundles and flat connections over compact Sasakian manifolds
[ 講演概要 ]
It is known that on a compact Kähler manifold, there is a correspondence between semisimple flat vector bundles and polystable higgs bundles with vanishing Chern classes via harmonic metrics (Simpson-Corlette). The purpose of this talk is to give the Sasakian (odd dimensional analogue of Kähler geometry) version of this correspondence. We prove that on a compact Sasakian manifold, there is an correspondence between semisimple flat vector bundles and the polystable basic Higgs bundles with vanishing basic Chern classes. (Joint work with Indranil Biswas, arXiv:1905.06178)
[ 参考URL ]
https://forms.gle/vSFPoVR6ugrkTGhX7

### 2020年05月14日(木)

#### 作用素環セミナー

16:45-18:15   オンライン開催

Connes' bicentralizer problem for q-deformed Araki-Woods algebras (English)
[ 参考URL ]
https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm

#### 情報数学セミナー

16:50-18:35   オンライン開催

[ 講演概要 ]
URL
[学内用] https://bit.ly/2zCBj8x (g.ecc.u-tokyo.ac.jpアカウントでアクセスできます)

機械学習と深層学習の登場で、AIは、コンピュータサイエンスの研究対象から、実用段階に入った。そして、あらゆる学術分野・産業分野における研究対象、事業対象へと変貌を遂げた。本講演では、今日のAI研究とAIビジネスの過去・現在・未来について展望する。

### 2020年05月13日(水)

#### 代数学コロキウム

17:30-18:30   オンライン開催
Yifeng Liu 氏 (Yale University)
On the Beilinson-Bloch-Kato conjecture for Rankin-Selberg motives (ENGLISH)
[ 講演概要 ]
In this talk, we will explain the final outcome on the Beilinson-Bloch-Kato conjecture for motives coming from certain automorphic representations of GL(n) x GL(n+1), of our recent project with Yichao Tian, Liang Xiao, Wei Zhang, and Xinwen Zhu. In particular, we show that the nonvanishing of the central L-value of the motive implies the vanishing of the corresponding Bloch-Kato Selmer group. We will also explain the main ideas and ingredients of the proof.
[ 参考URL ]
https://www.ms.u-tokyo.ac.jp/~t-saito/todai_IHES.html

### 2020年05月07日(木)

#### 情報数学セミナー

16:50-18:35   数理科学研究科棟(駒場) Zoom（詳細は講演概要に記載）号室

AIと量子計算（暗号理論を含む）を主題とする新たな数理科学

『私たちは誰？どこから来たのか？私たちはどこにいるのか？
私たちはどこへ行くのか？そのための数理科学の役割とは？』
～社会課題解決型と基礎理論回帰型アプローチの新学問体系の確立へ向けて～ (Japanese)
[ 講演概要 ]

[学内用] https://bit.ly/2zCBj8x (g.ecc.u-tokyo.ac.jpアカウントでアクセスできます)

【目次】
１．私たちは誰？（私の場合）
２．私たちはどこから来たのか？（私の場合）
３．私たちはどこにいるのか？
４．私たちはどこへ行くのか？
５．アントレプレナーシップとオープンイノベーションとは？
～産学連携の方向性とは？～

#### 作用素環セミナー

16:45-18:15   オンライン開催

A new construction of deformation quantization for Lagrangian fiber bundles (English)
[ 参考URL ]
https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm

### 2020年05月01日(金)

#### 統計数学セミナー

17:00-18:10   数理科学研究科棟(駒場) φ号室
Zoomでの開催となります。３日前までに講演参考URLから参加申込みをしてください。
Xiao Fang 氏 (Chinese University of Hong Kong)
High order distributional approximations by Stein's method (ENGLISH)
[ 講演概要 ]
Stein's method is a powerful tool to proving distributional approximations with error bounds. In this talk, we present two recent developments of Stein's method for high order approximations. (1) Together with Li Luo and Qi-Man Shao, we consider skewness correction in normal approximation. We prove a refined Cram¥'er-type moderate deviation result for a class of statistics possessing a local structure. We discuss applications to k-runs, U-statistics and subgraph counts. (2) Together with Anton Braverman and Jim Dai, we derive and justify new diffusion approximations with state-dependent diffusion coefficients for stationary distributions of Markov chains. We discuss applications to the Erlang-C system, a hospital inpatient flow model and the auto-regressive model.
[ 参考URL ]

### 2020年04月30日(木)

#### 作用素環セミナー

16:45-18:15   オンライン開催
Felix Parraud 氏 (ENS Lyon)
Interpolation between random matrices and their free limit with the help of free stochastic processes (English)
[ 参考URL ]
https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm

### 2020年04月23日(木)

#### 作用素環セミナー

16:45-18:15   オンライン開催

Lattice isomorphisms between projection lattices of von Neumann algebras
[ 参考URL ]
https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm

### 2020年04月22日(水)

#### 代数学コロキウム

17:30-18:30   オンライン開催
Arthur-César Le Bras 氏 (CNRS & Université Paris 13)
Prismatic Dieudonné theory (ENGLISH)
[ 講演概要 ]
I would like to explain a classification result for p-divisible groups, which unifies many of the existing results in the literature. The main tool is the theory of prisms and prismatic cohomology recently developed by Bhatt and Scholze. This is joint work with Johannes Anschütz.

### 2020年04月16日(木)

#### 統計数学セミナー

17:00-18:10   数理科学研究科棟(駒場) φ号室
Zoomでの開催となります。３日前までに講演参考URLから参加申込みをしてください。

Hawkes process and Edgeworth expansion with application to Maximum Likelihood Estimator (JAPANESE)
[ 講演概要 ]
The Hawkes process is a point process with a self-exciting property. It has been used to model earthquakes, social media events, infections, etc. and is getting a lot of attention. However, as a real problem, there are often situations where we can not obtain data with sufficient observation time. In such cases, it is not appropriate to approximate the error distribution of an estimator by the normal distribution. We established the Edgeworth expansion for a functional of a geometric mixing process, and applied this scheme to a functional of the Hawkes process with an exponential kernel. Furthermore, we gave a more appropriate asymptotic distribution for the error of the Maximum Likelihood Estimator of the Hawks process, i.e. a higher-order asymptotic distribution than the normal distribution. Here, in addition to the details of these statements, we also present the simulation results.
[ 参考URL ]

#### 作用素環セミナー

16:45-18:15   オンライン開催
Cyril Houdayer 氏 (Univ. Paris-Sud)
Structure theorem for unitary representations of irreducible lattices in product groups
[ 参考URL ]
https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm

### 2020年03月26日(木)

#### 談話会・数理科学講演会

16:00-17:00   数理科学研究科棟(駒場) 117号室

モノドロミー表現とその高次圏への拡張 (JAPANESE)

### 2020年03月02日(月)

#### 代数幾何学セミナー

15:30-17:00   数理科学研究科棟(駒場) 002号室

Evgeny Shinder 氏 (The University of Sheffield)
Semiorthogonal decompositions for singular varieties (English)
[ 講演概要 ]
I will define the semiorthogonal decomposition for derived categories of singular projective varieties due to Professor Kawamata, into finite-dimensional algebras, generalizing the concept of an exceptional collection in the smooth case. I will present known constructions of these for nodal curves (Burban), torsion-free toric surfaces (Karmazyn-Kuznetsov-Shinder) and two nodal threefolds (Kawamata). I will also explain obstructions coming from the K_{-1} group, and how it translates to maximal nonfactoriality in the nodal threefold case. This is joint work with M.Kalck and N.Pavic.

### 2020年02月28日(金)

#### PDE実解析研究会

16:00-17:00   数理科学研究科棟(駒場) 370号室

Maximilian Moser 氏 (University of Regensburg)
Convergence of the Allen-Cahn equation with a nonlinear Robin-boundary condition to mean curvature flow with constant contact angle (English)
[ 講演概要 ]
In this talk I will present a result for the sharp interface limit of the Allen-Cahn equation with a nonlinear Robin boundary condition in a two-dimensional domain, in the situation where an interface has developed and intersects the boundary. The boundary condition is designed in such a way that one obtains as the limit problem the mean curvature flow with constant contact angle. Convergence using strong norms is shown for contact angles close to 90° and small times, when a smooth solution to the limit problem exists. For the proof the method of de Mottoni and Schatzman is used: we construct an approximate solution for the Allen-Cahn system using asymptotic expansions based on the solution to the limit problem. Then we estimate the difference of the exact and approximate solution with a spectral estimate for the linearized (at the approximate solution) Allen-Cahn operator.
This is joint work with Helmut Abels from Regensburg.

### 2020年02月21日(金)

#### 代数幾何学セミナー

13:30-15:00   数理科学研究科棟(駒場) 370号室
いつもと曜日・時間・部屋が異なります
Jakub Witaszek 氏 (Michigan)
Keel's theorem and quotients in mixed characteristic (English)
[ 講演概要 ]
In trying to understand characteristic zero varieties one can apply a wide range of techniques coming from analytic methods such as vanishing theorems. More complicated though they are, positive characteristic varieties come naturally with Frobenius action which sometimes allows for imitating analytic proofs or even showing results which are false over complex numbers. Of all the three classes, the mixed characteristic varieties are the most difficult to understand as they represent the worst of both worlds: one lacks the analytic methods as well the Frobenius action.

What is key for many applications of Frobenius in positive characteristic (to birational geometry, moduli theory, constructing quotients, etc.) is the fact that every universal homeomorphism of algebraic varieties factors through a power of Frobenius. In this talk I will discuss an analogue of this fact (and applications thereof) in mixed characteristic.
[ 参考URL ]
http://www-personal.umich.edu/~jakubw/

### 2020年02月18日(火)

#### 解析学火曜セミナー

16:50-18:20   数理科学研究科棟(駒場) 128号室

Alessio Porretta 氏 (Tor Vergata university of Rome)
Long time behavior of mean field games systems (English)
[ 講演概要 ]
I will review several aspects related to the long time ergodic behavior of mean field game systems: the turnpike property, the exponential rate of convergence, the role of monotonicity of the couplings, the convergence of u up to translations, the limit of the vanishing discounted problem, the long time behavior of the master equation. All those aspects have independent interest and are correlated at the same time.

#### 東京無限可積分系セミナー

15:00-16:00   数理科学研究科棟(駒場) 002号室
Vincent Pasquier 氏 (IPhT Saclay)
Hydrodynamics of a one dimensional lattice gas.
(ENGLISH)
[ 講演概要 ]
The simplest boxball model is a one dimensional lattice gas obtained as
a certain (cristal) limit of the six vertex model where the evolution
determined by the transfer matrix becomes deterministic. One can
study its thermodynamics in and out of equilibrium and we shall present
preliminary results in this direction.

Collaboration with Atsuo Kuniba and Grégoire Misguich.

### 2020年02月17日(月)

#### 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

Precompactness of the moduli space of pseudo-normed graded algebras
[ 講演概要 ]
Graded algebras (such as canonical rings) coming from the spaces of sections of polarized algebraic varieties are studied by many mathematicians. On the other hand, the pseudo-norm project proposed by S.-T. Yau and C.-Y. Chi gives us a new differential geometric aspect of the Torelli type theorem.
In this talk, we give the details of how the geometry of pseudo-normed graded algebras allows us to obtain a natural compactification of the moduli space of pseudo-normed graded algebras.
(1) For a sequence of pseudo-normed graded algebras (of the same type), the above precompactness gives us some limit different from the Gromov-Hausdorff limit in Riemannian geometry.
(2) As an example of our construction, we have the Deligne-Mumford compactification, in which the notion of the orthogonal direct sum of pseudo-normed spaces comes up naturally. We also have a higher dimensional analogue by using weight filtration.

#### 離散数理モデリングセミナー

16:30-18:30   数理科学研究科棟(駒場) 126号室
Sanjay Ramassamy 氏 (IPhT, CEA Saclay)
Cluster algebras, dimer models and geometric dynamics
[ 講演概要 ]
Cluster algebras were introduced by Fomin and Zelevinsky at the beginning of the 21st century and have since then been related to several areas of mathematics. In this talk I will describe cluster algebras coming from quivers and give two concrete situations were they arise. The first is the bipartite dimer model coming from statistical mechanics. The second is in several dynamics on configurations of points/lines/circles/planes.

This is based on joint work with Niklas Affolter (TU Berlin), Max Glick (Google) and Pavlo Pylyavskyy (University of Minnesota).