## Seminar information archive

Seminar information archive ～09/18｜Today's seminar 09/19 | Future seminars 09/20～

#### Operator Algebra Seminars

16:45-18:15 Online

On Arveson's boundary theorem (English)

[ Reference URL ]

https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm

**Yoshimichi Ueda**(Nagoya Univ.)On Arveson's boundary theorem (English)

[ Reference URL ]

https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm

### 2020/06/17

#### Number Theory Seminar

17:30-18:30 Online

On modular representations of GL_2(L) for unramified L (ENGLISH)

https://www.ms.u-tokyo.ac.jp/~t-saito/todai_IHES.html

**Christophe Breuil**(CNRS, Université Paris-Sud)On modular representations of GL_2(L) for unramified L (ENGLISH)

[ Abstract ]

Let p be a prime number and L a finite unramified extension of Q_p. We give a survey of past and new results on smooth admissible representations of GL_2(L) that appear in mod p cohomology. This is joint work with Florian Herzig, Yongquan Hu, Stefano Morra and Benjamin Schraen.

[ Reference URL ]Let p be a prime number and L a finite unramified extension of Q_p. We give a survey of past and new results on smooth admissible representations of GL_2(L) that appear in mod p cohomology. This is joint work with Florian Herzig, Yongquan Hu, Stefano Morra and Benjamin Schraen.

https://www.ms.u-tokyo.ac.jp/~t-saito/todai_IHES.html

### 2020/06/11

#### Operator Algebra Seminars

16:45-18:15 Online

Homology and K-theory of torsion free ample groupoids and Smale spaces (English)

[ Reference URL ]

https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm

**Makoto Yamashita**(Univ. Oslo)Homology and K-theory of torsion free ample groupoids and Smale spaces (English)

[ Reference URL ]

https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm

#### Information Mathematics Seminar

16:50-18:35 Online

Big picture of the modern AI and Machine learning in the basics (Japanese)

[学外用] https://docs.google.com/forms/d/1d1RWvV8j1TzXg8eF93zMZeIzJeIvdq9zY8htO8w2St0/ [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)

**Hiroshi Fujiwara**(BroadBand Tower, Inc.)Big picture of the modern AI and Machine learning in the basics (Japanese)

[ Abstract ]

Explanation of the modern AI and Machine learning

[ Reference URL ]Explanation of the modern AI and Machine learning

[学外用] https://docs.google.com/forms/d/1d1RWvV8j1TzXg8eF93zMZeIzJeIvdq9zY8htO8w2St0/ [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)

### 2020/06/08

#### Seminar on Geometric Complex Analysis

10:30-12:00 Online

Applications of the Quot-scheme limit to variational aspects of the Hermitian-Einstein metric

https://forms.gle/vSFPoVR6ugrkTGhX7

**HASHIMOTO Yoshinori**(Tokyo Institute of Technology)Applications of the Quot-scheme limit to variational aspects of the Hermitian-Einstein metric

[ Abstract ]

The Kobayashi-Hitchin correspondence, proved by Donaldson and Uhlenbeck-Yau by using the nonlinear PDE theory, states that the existence of Hermitian-Einstein metrics on a holomorphic vector bundle is equivalent to an algebro-geometric stability condition. We present some results that exhibit an explicit link between differential and algebraic geometry in the above correspondence, from a variational point of view. The key to such results is an object called the Quot-scheme limit of Fubini-Study metrics, which is used to evaluate certain algebraic 1-parameter subgroups of Hermitian metrics by using the theory of Quot-schemes in algebraic geometry. This method also works for the proof of the correspondence between the balanced metrics and the Gieseker stability, as originally proved by X.W. Wang. Joint work with Julien Keller.

[ Reference URL ]The Kobayashi-Hitchin correspondence, proved by Donaldson and Uhlenbeck-Yau by using the nonlinear PDE theory, states that the existence of Hermitian-Einstein metrics on a holomorphic vector bundle is equivalent to an algebro-geometric stability condition. We present some results that exhibit an explicit link between differential and algebraic geometry in the above correspondence, from a variational point of view. The key to such results is an object called the Quot-scheme limit of Fubini-Study metrics, which is used to evaluate certain algebraic 1-parameter subgroups of Hermitian metrics by using the theory of Quot-schemes in algebraic geometry. This method also works for the proof of the correspondence between the balanced metrics and the Gieseker stability, as originally proved by X.W. Wang. Joint work with Julien Keller.

https://forms.gle/vSFPoVR6ugrkTGhX7

### 2020/06/05

#### Colloquium

15:30-16:30 Online

Please register at the link below to attend this online colloquium

Exact WKB analysis and related topics

https://zoom.us/webinar/register/WN_ezXY3HjIQcCK2G9V-2CYrw

Please register at the link below to attend this online colloquium

**Kohei Iwaki**(Graduate School of Mathematical Sciences, University of Tokyo)Exact WKB analysis and related topics

[ Abstract ]

Exact WKB analysis, developed by Voros et.al., is an effective method for global study of (singularly perturbed) ordinary differential equations defined on a complex domain. After recalling several fundamental facts on exact WKB analysis, I'll talk about relationships to other research topics, such as cluster algebras, topological recursion, integrable systems of Painlevé type, etc.

[ Reference URL ]Exact WKB analysis, developed by Voros et.al., is an effective method for global study of (singularly perturbed) ordinary differential equations defined on a complex domain. After recalling several fundamental facts on exact WKB analysis, I'll talk about relationships to other research topics, such as cluster algebras, topological recursion, integrable systems of Painlevé type, etc.

https://zoom.us/webinar/register/WN_ezXY3HjIQcCK2G9V-2CYrw

### 2020/06/04

#### Operator Algebra Seminars

16:45-18:15 Online

Equivariant $O_2$-absorption theorem for exact groups

**Yuhei Suzuki**(Hokkaido Univ.)Equivariant $O_2$-absorption theorem for exact groups

#### Information Mathematics Seminar

16:50-18:35 Online

Telework society and importance of the cyber security to increase

**Hiroshi Fujiwara**(BroadBand Tower, Inc.)Telework society and importance of the cyber security to increase

[ Abstract ]

Explanation on telework society and importance of the cyber security

Explanation on telework society and importance of the cyber security

### 2020/05/28

#### Operator Algebra Seminars

16:45-18:15 Online

Index theorem of lattice Wilson-Dirac operators and almost-commuting matrices (English)

[ Reference URL ]

https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm

**Yosuke Kubota**(Shinshu Univ.)Index theorem of lattice Wilson-Dirac operators and almost-commuting matrices (English)

[ Reference URL ]

https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm

### 2020/05/27

#### Number Theory Seminar

17:30-18:30 Online

Shintani generating class and the p-adic polylogarithm for totally real fields (ENGLISH)

https://www.ms.u-tokyo.ac.jp/~t-saito/todai_IHES.html

**Kenichi Bannai**(Keio University/RIKEN)Shintani generating class and the p-adic polylogarithm for totally real fields (ENGLISH)

[ Abstract ]

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.

[ Reference URL ]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.

https://www.ms.u-tokyo.ac.jp/~t-saito/todai_IHES.html

### 2020/05/25

#### Seminar on Geometric Complex Analysis

10:30-12:00 Online

Characteristic forms of Cheng-Yau metric and CR invariants

[ Reference URL ]

https://forms.gle/vSFPoVR6ugrkTGhX7

**MARUGAME Taiji**(Riken AIP - Osaka University)Characteristic forms of Cheng-Yau metric and CR invariants

[ Reference URL ]

https://forms.gle/vSFPoVR6ugrkTGhX7

### 2020/05/21

#### Information Mathematics Seminar

16:50-18:35 Online

From the birth of the computer to further speedup of the calculation speed

(Japanese)

https://docs.google.com/forms/d/1d1RWvV8j1TzXg8eF93zMZeIzJeIvdq9zY8htO8w2St0/

**Hiroshi Fujiwara**(BroadBand Tower, Inc.)From the birth of the computer to further speedup of the calculation speed

(Japanese)

[ Abstract ]

Explanation of the birth of computer and the further speedup of calculation speed

[ Reference URL ]Explanation of the birth of computer and the further speedup of calculation speed

https://docs.google.com/forms/d/1d1RWvV8j1TzXg8eF93zMZeIzJeIvdq9zY8htO8w2St0/

#### Operator Algebra Seminars

16:45-18:15 Online

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

**Takuya Takeishi**(Kyoto Institute of Technology)Partition functions as $C^*$-dynamical invariants and actions of congruence monoids (English)

### 2020/05/18

#### Seminar on Geometric Complex Analysis

10:30-12:00 Online

Higgs bundles and flat connections over compact Sasakian manifolds

https://forms.gle/vSFPoVR6ugrkTGhX7

**KASUYA Hisashi**(Osaka University)Higgs bundles and flat connections over compact Sasakian manifolds

[ Abstract ]

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)

[ Reference URL ]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)

https://forms.gle/vSFPoVR6ugrkTGhX7

### 2020/05/14

#### Operator Algebra Seminars

16:45-18:15 Online

Connes' bicentralizer problem for q-deformed Araki-Woods algebras (English)

[ Reference URL ]

https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm

**Yusuke Isono**(RIMS, Kyoto Univ.)Connes' bicentralizer problem for q-deformed Araki-Woods algebras (English)

[ Reference URL ]

https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm

#### Information Mathematics Seminar

16:50-18:35 Online

The past, the present, the future of the AI that a practical use stage began (Japanese)

**Hiroshi Fujiwara**(BroadBand Tower, Inc.)The past, the present, the future of the AI that a practical use stage began (Japanese)

[ Abstract ]

The explanation on the past, the present, the future of the AI that a practical use stage began

The explanation on the past, the present, the future of the AI that a practical use stage began

### 2020/05/13

#### Number Theory Seminar

17:30-18:30 Online

On the Beilinson-Bloch-Kato conjecture for Rankin-Selberg motives (ENGLISH)

https://www.ms.u-tokyo.ac.jp/~t-saito/todai_IHES.html

**Yifeng Liu**(Yale University)On the Beilinson-Bloch-Kato conjecture for Rankin-Selberg motives (ENGLISH)

[ Abstract ]

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.

[ Reference URL ]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.

https://www.ms.u-tokyo.ac.jp/~t-saito/todai_IHES.html

### 2020/05/07

#### Information Mathematics Seminar

16:50-18:35 Room #Zoom（詳細は講演概要に記載） (Graduate School of Math. Sci. Bldg.)

"Who are we? Where have we come from? Where are we?

Where will we go? What is the role of the mathematical science?"

～To establish of the new academic system by the basic theory regression

type approach and the social problem solving type approach～

(Japanese)

**Hiroshi Fujiwara**(BroadBand Tower, Inc.)"Who are we? Where have we come from? Where are we?

Where will we go? What is the role of the mathematical science?"

～To establish of the new academic system by the basic theory regression

type approach and the social problem solving type approach～

(Japanese)

#### Operator Algebra Seminars

16:45-18:15 Online

A new construction of deformation quantization for Lagrangian fiber bundles (English)

[ Reference URL ]

https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm

**Mayuko Yamashita**(RIMS, Kyoto Univ.)A new construction of deformation quantization for Lagrangian fiber bundles (English)

[ Reference URL ]

https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm

### 2020/05/01

#### Seminar on Probability and Statistics

17:00-18:10 Room #φ (Graduate School of Math. Sci. Bldg.)

High order distributional approximations by Stein's method (ENGLISH)

https://docs.google.com/forms/d/e/1FAIpQLSeSVwYsjhyQQXzjt3ZpvRh9ZEO5qZXxxLxYDYOu301Mc89RCA/viewform

**Xiao Fang**(Chinese University of Hong Kong)High order distributional approximations by Stein's method (ENGLISH)

[ Abstract ]

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.

[ Reference URL ]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.

https://docs.google.com/forms/d/e/1FAIpQLSeSVwYsjhyQQXzjt3ZpvRh9ZEO5qZXxxLxYDYOu301Mc89RCA/viewform

### 2020/04/30

#### Operator Algebra Seminars

16:45-18:15 Online

Interpolation between random matrices and their free limit with the help of free stochastic processes (English)

[ Reference URL ]

https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm

**Felix Parraud**(ENS Lyon)Interpolation between random matrices and their free limit with the help of free stochastic processes (English)

[ Reference URL ]

https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm

### 2020/04/23

#### Operator Algebra Seminars

16:45-18:15 Online

Lattice isomorphisms between projection lattices of von Neumann algebras

[ Reference URL ]

https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm

**Michiya Mori**(Univ. Tokyo)Lattice isomorphisms between projection lattices of von Neumann algebras

[ Reference URL ]

https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm

### 2020/04/22

#### Number Theory Seminar

17:30-18:30 Online

Prismatic Dieudonné theory (ENGLISH)

**Arthur-César Le Bras**(CNRS & Université Paris 13)Prismatic Dieudonné theory (ENGLISH)

[ Abstract ]

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.

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.

### 2020/04/16

#### Seminar on Probability and Statistics

17:00-18:10 Room #φ (Graduate School of Math. Sci. Bldg.)

Hawkes process and Edgeworth expansion with application to Maximum Likelihood Estimator (JAPANESE)

https://docs.google.com/forms/d/18MDagC71CtB7SJmW2s0tPIBW9YDUNWH5XH1uby2W6Xc/edit

**Masatoshi Goda**(University of Tokyo)Hawkes process and Edgeworth expansion with application to Maximum Likelihood Estimator (JAPANESE)

[ Abstract ]

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.

[ Reference URL ]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.

https://docs.google.com/forms/d/18MDagC71CtB7SJmW2s0tPIBW9YDUNWH5XH1uby2W6Xc/edit

#### Operator Algebra Seminars

16:45-18:15 Online

Structure theorem for unitary representations of irreducible lattices in product groups

[ Reference URL ]

https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm

**Cyril Houdayer**(Univ. Paris-Sud)Structure theorem for unitary representations of irreducible lattices in product groups

[ Reference URL ]

https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm

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