## Seminar information archive

Seminar information archive ～11/07｜Today's seminar 11/08 | Future seminars 11/09～

#### Lie Groups and Representation Theory

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

Online

Computation of weighted Bergman inner products on bounded symmetric domains and restriction to subgroups (Japanese)

Online

**Ryosuke NAKAHAMA**(Kyushu University)Computation of weighted Bergman inner products on bounded symmetric domains and restriction to subgroups (Japanese)

[ Abstract ]

Let $D¥subset M(r,¥mathbb{C})$ be the bounded symmetric domain, and we consider the weighted Bergman space $¥mathcal{H}_¥lambda(D)$ on $D$. Then $SU(r,r)$ acts unitarily on $¥mathcal{H}_¥lambda(D)$.

In this seminar, we compute explicitly the inner products for some polynomials on $¥operatorname{Alt}(r,¥mathbb{C})$, $¥operatorname{Sym}(r,¥mathbb{C})¥subset M(r,¥mathbb{C})$, and prove that the inner products are given by multivariate hypergeometric polynomials when the polynomials are some powers of the determinants or the Pfaffians.

As an application, we present the results on the construction of symmetry breaking operators from $SU(r,r)$ to $Sp(r,¥mathbb{R})$ or $SO^*(2r)$.

Let $D¥subset M(r,¥mathbb{C})$ be the bounded symmetric domain, and we consider the weighted Bergman space $¥mathcal{H}_¥lambda(D)$ on $D$. Then $SU(r,r)$ acts unitarily on $¥mathcal{H}_¥lambda(D)$.

In this seminar, we compute explicitly the inner products for some polynomials on $¥operatorname{Alt}(r,¥mathbb{C})$, $¥operatorname{Sym}(r,¥mathbb{C})¥subset M(r,¥mathbb{C})$, and prove that the inner products are given by multivariate hypergeometric polynomials when the polynomials are some powers of the determinants or the Pfaffians.

As an application, we present the results on the construction of symmetry breaking operators from $SU(r,r)$ to $Sp(r,¥mathbb{R})$ or $SO^*(2r)$.

### 2021/05/10

#### Seminar on Geometric Complex Analysis

10:30-12:00 Online

強擬凹複素曲面の境界に現れる接触構造 (Japanese)

https://u-tokyo-ac-jp.zoom.us/meeting/register/tJ0vcu2rrDIqG9Rv5AT0Mpi37urIkJ1IRldB

**Naohiko Kasuya**(Hokkaido University)強擬凹複素曲面の境界に現れる接触構造 (Japanese)

[ Abstract ]

強擬凸複素曲面の境界は3次元強擬凸CR多様体であり、正の接触構造を誘導する。BogomolovとDe Oliveiraは強擬凸複素曲面の境界に現れる接触構造はStein fillableであること（CR構造としては、Stein fillableなものに変形同値であること）を示した。

一方、強擬凹複素曲面の境界には負の3次元接触構造が現れる。本講演では、任意の負の3次元閉接触多様体が強擬凹複素曲面の境界として実現可能であることを示す。証明は、EliashbergによるStein manifoldの構成法を参考にして強擬凹境界への正則ハンドルの接着手法を確立することによってなされる。

尚、本講演内容はDaniele Zuddas氏（トリエステ大学）との共同研究である。

[ Reference URL ]強擬凸複素曲面の境界は3次元強擬凸CR多様体であり、正の接触構造を誘導する。BogomolovとDe Oliveiraは強擬凸複素曲面の境界に現れる接触構造はStein fillableであること（CR構造としては、Stein fillableなものに変形同値であること）を示した。

一方、強擬凹複素曲面の境界には負の3次元接触構造が現れる。本講演では、任意の負の3次元閉接触多様体が強擬凹複素曲面の境界として実現可能であることを示す。証明は、EliashbergによるStein manifoldの構成法を参考にして強擬凹境界への正則ハンドルの接着手法を確立することによってなされる。

尚、本講演内容はDaniele Zuddas氏（トリエステ大学）との共同研究である。

https://u-tokyo-ac-jp.zoom.us/meeting/register/tJ0vcu2rrDIqG9Rv5AT0Mpi37urIkJ1IRldB

### 2021/05/06

#### Tokyo-Nagoya Algebra Seminar

16:00-17:30 Online

Please see the URL below for details on the online seminar.

Derived quotients of Cohen-Macaulay rings (English)

http://www.math.nagoya-u.ac.jp/~aaron.chan/TNAseminar.html

Please see the URL below for details on the online seminar.

**Liran Shaul**(Charles University)Derived quotients of Cohen-Macaulay rings (English)

[ Abstract ]

It is well known that if A is a Cohen-Macaulay ring and $a_1,\dots,a_n$ is an $A$-regular sequence, then the quotient ring $A/(a_1,\dots,a_n)$ is also a Cohen-Macaulay ring. In this talk we explain that by deriving the quotient operation, if A is a Cohen-Macaulay ring and $a_1,\dots,a_n$ is any sequence of elements in $A$, the derived quotient of $A$ with respect to $(a_1,\dots,a_n)$ is Cohen-Macaulay. Several applications of this result are given, including a generalization of Hironaka's miracle flatness theorem to derived algebraic geometry.

[ Reference URL ]It is well known that if A is a Cohen-Macaulay ring and $a_1,\dots,a_n$ is an $A$-regular sequence, then the quotient ring $A/(a_1,\dots,a_n)$ is also a Cohen-Macaulay ring. In this talk we explain that by deriving the quotient operation, if A is a Cohen-Macaulay ring and $a_1,\dots,a_n$ is any sequence of elements in $A$, the derived quotient of $A$ with respect to $(a_1,\dots,a_n)$ is Cohen-Macaulay. Several applications of this result are given, including a generalization of Hironaka's miracle flatness theorem to derived algebraic geometry.

http://www.math.nagoya-u.ac.jp/~aaron.chan/TNAseminar.html

#### Information Mathematics Seminar

16:50-18:35 Online

From the birth of the computer to high-speed computing (Japanese)

https://docs.google.com/forms/d/1zdmPdHWcVgH6Sn62nVHNp0ODVBJ7fyHKJHdABtDd_Tw

**Hiroshi Fujiwara**(BroadBand Tower, Inc.)From the birth of the computer to high-speed computing (Japanese)

[ Abstract ]

Explanation on the birth of the computer and the development of high-speed computing

[ Reference URL ]Explanation on the birth of the computer and the development of high-speed computing

https://docs.google.com/forms/d/1zdmPdHWcVgH6Sn62nVHNp0ODVBJ7fyHKJHdABtDd_Tw

### 2021/04/30

#### Colloquium

15:30-16:30 Online

Registration is closed (12:00, April 30).

Uniform bound of the number of weighted blow-ups to compute the minimal log discrepancy for smooth 3-folds (Talk in Japanese, Slide in English)

Registration is closed (12:00, April 30).

**Shihoko Ishii**(The University of Tokyo)Uniform bound of the number of weighted blow-ups to compute the minimal log discrepancy for smooth 3-folds (Talk in Japanese, Slide in English)

[ Abstract ]

In the talk I will show that the minimal log discrepancy of every pair consisting of a smooth 3-fold and a "general" real ideal is computed by the divisor obtained by at most two weighted blow ups. Our proof suggests the following conjecture:

Every pair consisting of a smooth N-fold and a "general" real ideal is computed by a divisor obtained by at most N-1 weighted blow ups.

This is regarded as a weighted blow up version of Mustata-Nakamura's conjecture. The condition "general" is slightly weakened from the version presented in ZAG Seminar.

In the talk I will show that the minimal log discrepancy of every pair consisting of a smooth 3-fold and a "general" real ideal is computed by the divisor obtained by at most two weighted blow ups. Our proof suggests the following conjecture:

Every pair consisting of a smooth N-fold and a "general" real ideal is computed by a divisor obtained by at most N-1 weighted blow ups.

This is regarded as a weighted blow up version of Mustata-Nakamura's conjecture. The condition "general" is slightly weakened from the version presented in ZAG Seminar.

### 2021/04/28

#### Algebraic Geometry Seminar

15:00-16:00 Room #Zoom (Graduate School of Math. Sci. Bldg.)

Dimensional reduction in cohomological Donaldson-Thomas theory (日本語)

**Tasuki Kinjo**(Tokyo/IPMU)Dimensional reduction in cohomological Donaldson-Thomas theory (日本語)

[ Abstract ]

None

None

### 2021/04/27

#### Numerical Analysis Seminar

16:30-18:00 Online

Rigorous numerics for nonlinear heat equations in the complex plane of time (Japanese)

[ Reference URL ]

https://forms.gle/qW5ktphBB6dsh8Np7

**Akitoshi Takayasu**(University of Tsukuba)Rigorous numerics for nonlinear heat equations in the complex plane of time (Japanese)

[ Reference URL ]

https://forms.gle/qW5ktphBB6dsh8Np7

#### Operator Algebra Seminars

16:45-18:15 Online

The bulk-boundary correspondence for topological insulators on lattices with screw dislocation

[ Reference URL ]

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

**Yosuke Kubota**(Shinshu Univ.)The bulk-boundary correspondence for topological insulators on lattices with screw dislocation

[ Reference URL ]

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

#### Tuesday Seminar on Topology

17:00-18:00 Online

Pre-registration required. See our seminar webpage.

On a singular de Rham complex in diffeology (JAPANESE)

https://u-tokyo-ac-jp.zoom.us/meeting/register/tJUpcOCppzwpGd3r_XqdszQ1XN6FvXpNURbj

Pre-registration required. See our seminar webpage.

**Katsuhiko Kuribayashi**(Shinshu University)On a singular de Rham complex in diffeology (JAPANESE)

[ Abstract ]

Diffeology gives a complete, co-complete, cartesian closed category into which the category of manifolds embeds. In the framework of diffeology, the de Rham complex in the sense of Souriau enables us to develop de Rham calculus. Moreover,Iglesias-Zemmour has been introduced homotopical concepts such as homotopy groups, cubic homology groups and fibrations in diffeology. Thus one might expect `differential homotopy theory'. However, the de Rham theorem does not hold for Souriau's cochain

complex in general. In this talk, I will introduce a singular de Rham complex endowed with an integration map into the singular cochain complex which gives the de Rham theorem for every diffeological space.

[ Reference URL ]Diffeology gives a complete, co-complete, cartesian closed category into which the category of manifolds embeds. In the framework of diffeology, the de Rham complex in the sense of Souriau enables us to develop de Rham calculus. Moreover,Iglesias-Zemmour has been introduced homotopical concepts such as homotopy groups, cubic homology groups and fibrations in diffeology. Thus one might expect `differential homotopy theory'. However, the de Rham theorem does not hold for Souriau's cochain

complex in general. In this talk, I will introduce a singular de Rham complex endowed with an integration map into the singular cochain complex which gives the de Rham theorem for every diffeological space.

https://u-tokyo-ac-jp.zoom.us/meeting/register/tJUpcOCppzwpGd3r_XqdszQ1XN6FvXpNURbj

### 2021/04/26

#### Seminar on Geometric Complex Analysis

10:30-12:00 Online

多様体の留数 (Japanese)

https://u-tokyo-ac-jp.zoom.us/meeting/register/tJ0vcu2rrDIqG9Rv5AT0Mpi37urIkJ1IRldB

**Jun O'Hara**(Chiba University)多様体の留数 (Japanese)

[ Abstract ]

$M$を多様体、$z$を複素数とし、$M$の二点間の距離の$z$乗を積空間$M\times M$上積分したものを考えると、$z$の実部が大きいところで$z$の正則関数になる。解析接続により複素平面上の有理関数で1位の極のみ持つものが得られる。この有理型関数、特にその留数の性質を紹介する。具体的には、メビウス不変性、留数と似た量（曲面のWillmoreエネルギー、4次元多様体のGraham-Wittenエネルギー、積分幾何で出てくる内在的体積、ラプラシアンのスペクトルなど）との比較、有理型関数・留数による多様体の同定問題などを扱う。

参考資料：https://sites.google.com/site/junohara/ ダウンロード 「多様体のエネルギーと留数」（少し古い）, arXiv:2012.01713

[ Reference URL ]$M$を多様体、$z$を複素数とし、$M$の二点間の距離の$z$乗を積空間$M\times M$上積分したものを考えると、$z$の実部が大きいところで$z$の正則関数になる。解析接続により複素平面上の有理関数で1位の極のみ持つものが得られる。この有理型関数、特にその留数の性質を紹介する。具体的には、メビウス不変性、留数と似た量（曲面のWillmoreエネルギー、4次元多様体のGraham-Wittenエネルギー、積分幾何で出てくる内在的体積、ラプラシアンのスペクトルなど）との比較、有理型関数・留数による多様体の同定問題などを扱う。

参考資料：https://sites.google.com/site/junohara/ ダウンロード 「多様体のエネルギーと留数」（少し古い）, arXiv:2012.01713

https://u-tokyo-ac-jp.zoom.us/meeting/register/tJ0vcu2rrDIqG9Rv5AT0Mpi37urIkJ1IRldB

### 2021/04/22

#### Tokyo-Nagoya Algebra Seminar

16:00-17:30 Online

Please see the URL below for details on the online seminar.

Exact categories via A-infinity algebras (English)

http://www.math.nagoya-u.ac.jp/~aaron.chan/TNAseminar.html

Please see the URL below for details on the online seminar.

**Julian Külshammer**(Uppsala University)Exact categories via A-infinity algebras (English)

[ Abstract ]

Many instances of extension closed subcategories appear throughout representation theory, e.g. filtered modules, Gorenstein projectives, as well as modules of finite projective dimension. In the first part of the talk, I will outline a general strategy to realise such subcategories as categories of induced modules from a subalgebra using A-infinity algebras. In the second part, I will describe how this strategy has been successfully applied for the exact category of filtered modules over a quasihereditary algebra. In particular I will present compatibility results of this approach with heredity ideals in a quasihereditary algebra from joint work with Teresa Conde.

[ Reference URL ]Many instances of extension closed subcategories appear throughout representation theory, e.g. filtered modules, Gorenstein projectives, as well as modules of finite projective dimension. In the first part of the talk, I will outline a general strategy to realise such subcategories as categories of induced modules from a subalgebra using A-infinity algebras. In the second part, I will describe how this strategy has been successfully applied for the exact category of filtered modules over a quasihereditary algebra. In particular I will present compatibility results of this approach with heredity ideals in a quasihereditary algebra from joint work with Teresa Conde.

http://www.math.nagoya-u.ac.jp/~aaron.chan/TNAseminar.html

#### Applied Analysis

16:30-18:00 Online

Relaxation of Optimal Transport problem on finite state space via Bregman divergence (Japanese)

[ Reference URL ]

https://forms.gle/yg9XZDVdxYG6qMos8

**( )**Relaxation of Optimal Transport problem on finite state space via Bregman divergence (Japanese)

[ Reference URL ]

https://forms.gle/yg9XZDVdxYG6qMos8

#### Information Mathematics Seminar

16:50-18:35 Online

Look back on the half life of a challenge to Digital technology and Entrepreneurship (Japanese)

https://docs.google.com/forms/d/1zdmPdHWcVgH6Sn62nVHNp0ODVBJ7fyHKJHdABtDd_Tw

**Hiroshi Fujiwara**(BroadBand Tower, Inc.)Look back on the half life of a challenge to Digital technology and Entrepreneurship (Japanese)

[ Abstract ]

Recollection on the half life of a challenge to Digital technology and Entrepreneurship

[ Reference URL ]Recollection on the half life of a challenge to Digital technology and Entrepreneurship

https://docs.google.com/forms/d/1zdmPdHWcVgH6Sn62nVHNp0ODVBJ7fyHKJHdABtDd_Tw

### 2021/04/21

#### Algebraic Geometry Seminar

15:00-16:00 Room #ZOOM (Graduate School of Math. Sci. Bldg.)

A decomposition formula for J-stability and its applications (日本語)

**Masafumi Hattori**(Kyoto)A decomposition formula for J-stability and its applications (日本語)

[ Abstract ]

J-stability is an analog of K-stability and plays an important role in K-stability for general polarized varieties (not only for Kahler-Einstein metrics). Strikingly, G.Chen proved uniform J-stability and slope uniform J-stability are equivalent, analogous to Ross-Thomas slope theory and Mumford-Takemoto slope theory for vector bundles, by differential geometric arguments recently. However, this fact has not been proved in algebro-geometric way before. In this talk, I would like to explain a decomposition formula of non-Archimedean J-functional, the (n+1)-dimensional intersection number into n-dimensional intersection numbers and its applications to prove the fact for surfaces and to construct a K-stable but not uniformly K-stable lc pair. Based on arXiv:2103.04603

J-stability is an analog of K-stability and plays an important role in K-stability for general polarized varieties (not only for Kahler-Einstein metrics). Strikingly, G.Chen proved uniform J-stability and slope uniform J-stability are equivalent, analogous to Ross-Thomas slope theory and Mumford-Takemoto slope theory for vector bundles, by differential geometric arguments recently. However, this fact has not been proved in algebro-geometric way before. In this talk, I would like to explain a decomposition formula of non-Archimedean J-functional, the (n+1)-dimensional intersection number into n-dimensional intersection numbers and its applications to prove the fact for surfaces and to construct a K-stable but not uniformly K-stable lc pair. Based on arXiv:2103.04603

#### Seminar on Probability and Statistics

14:30-16:00 Room # (Graduate School of Math. Sci. Bldg.)

Stationary distribution approximations for two-island and seed bank models (ENGLISH)

https://docs.google.com/forms/d/e/1FAIpQLSfLezQNquom7pjodIrc1suI0o5rsWg9AHNv7cix0A7h39tx-g/viewform

**Han Liang Gan**(University of Waikato)Stationary distribution approximations for two-island and seed bank models (ENGLISH)

[ Abstract ]

Asia-Pacific Seminar in Probability and Statistics (APSPS)

https://sites.google.com/view/apsps/home

Two-island Wright-Fisher models are used to model genetic frequencies and variability for subdivided populations. One of the key components of the model is the level of migration between the two

islands. We show that as the population size increases, the appropriate approximation and limit for the stationary distribution of a two-island Wright-Fisher Markov chain depends on the level of migration. In a seed bank model, individuals in one of the islands stay dormant rather than reproduce. We give analogous results for the seed bank model, compare and contrast the differences and examine the effect the seed bank has on genetic variability. Our results are derived from a new development of Stein's method for the two-island diffusion model and existing results for Stein's method for the Dirichlet distribution.

This talk is based on joint work with Adrian Röllin, Nathan Ross and Maite Wilke Berenguer.

[ Reference URL ]Asia-Pacific Seminar in Probability and Statistics (APSPS)

https://sites.google.com/view/apsps/home

Two-island Wright-Fisher models are used to model genetic frequencies and variability for subdivided populations. One of the key components of the model is the level of migration between the two

islands. We show that as the population size increases, the appropriate approximation and limit for the stationary distribution of a two-island Wright-Fisher Markov chain depends on the level of migration. In a seed bank model, individuals in one of the islands stay dormant rather than reproduce. We give analogous results for the seed bank model, compare and contrast the differences and examine the effect the seed bank has on genetic variability. Our results are derived from a new development of Stein's method for the two-island diffusion model and existing results for Stein's method for the Dirichlet distribution.

This talk is based on joint work with Adrian Röllin, Nathan Ross and Maite Wilke Berenguer.

https://docs.google.com/forms/d/e/1FAIpQLSfLezQNquom7pjodIrc1suI0o5rsWg9AHNv7cix0A7h39tx-g/viewform

#### Seminar on Probability and Statistics

14:30-16:00 Room # (Graduate School of Math. Sci. Bldg.)

Stationary distribution approximations for two-island and seed bank models

https://docs.google.com/forms/d/e/1FAIpQLSfLezQNquom7pjodIrc1suI0o5rsWg9AHNv7cix0A7h39tx-g/viewform

**Han Liang Gan**(University of Waikato)Stationary distribution approximations for two-island and seed bank models

[ Abstract ]

Asia-Pacific Seminar in Probability and Statistics (APSPS)

https://sites.google.com/view/apsps/home

Two-island Wright-Fisher models are used to model genetic frequencies and variability for subdivided populations. One of the key components of the model is the level of migration between the two islands. We show that as the population size increases, the appropriate approximation and limit for the stationary distribution of a two-island Wright-Fisher Markov chain depends on the level of migration. In a seed bank model, individuals in one of the islands stay dormant rather than reproduce. We give analogous results for the seed bank model, compare and contrast the differences and examine the effect the seed bank has on genetic variability. Our results are derived from a new development of Stein's method for the two-island diffusion model and existing results for

Stein's method for the Dirichlet distribution.

This talk is based on joint work with Adrian Röllin, Nathan Ross and Maite Wilke Berenguer.

[ Reference URL ]Asia-Pacific Seminar in Probability and Statistics (APSPS)

https://sites.google.com/view/apsps/home

Two-island Wright-Fisher models are used to model genetic frequencies and variability for subdivided populations. One of the key components of the model is the level of migration between the two islands. We show that as the population size increases, the appropriate approximation and limit for the stationary distribution of a two-island Wright-Fisher Markov chain depends on the level of migration. In a seed bank model, individuals in one of the islands stay dormant rather than reproduce. We give analogous results for the seed bank model, compare and contrast the differences and examine the effect the seed bank has on genetic variability. Our results are derived from a new development of Stein's method for the two-island diffusion model and existing results for

Stein's method for the Dirichlet distribution.

This talk is based on joint work with Adrian Röllin, Nathan Ross and Maite Wilke Berenguer.

https://docs.google.com/forms/d/e/1FAIpQLSfLezQNquom7pjodIrc1suI0o5rsWg9AHNv7cix0A7h39tx-g/viewform

### 2021/04/20

#### Tuesday Seminar on Topology

17:00-18:00 Online

Pre-registration required. See our seminar webpage.

Realisation of measured laminations on boundaries of convex cores (JAPANESE)

https://u-tokyo-ac-jp.zoom.us/meeting/register/tJUpcOCppzwpGd3r_XqdszQ1XN6FvXpNURbj

Pre-registration required. See our seminar webpage.

**Ken’ichi Ohshika**(Gakushuin University)Realisation of measured laminations on boundaries of convex cores (JAPANESE)

[ Abstract ]

I shall present a generalisation of the theorem by Bonahon-Otal concerning realisation of measured laminations as bending laminations of geometrically finite groups, to general Kleinian surface groups which might be geometrically infinite. Our proof is based on analysis of geometric limits, and is independent of the technique of hyperbolic cone-manifolds employed by Bonahon-Otal. This is joint work with Shinpei Baba (Osaka Univ.).

[ Reference URL ]I shall present a generalisation of the theorem by Bonahon-Otal concerning realisation of measured laminations as bending laminations of geometrically finite groups, to general Kleinian surface groups which might be geometrically infinite. Our proof is based on analysis of geometric limits, and is independent of the technique of hyperbolic cone-manifolds employed by Bonahon-Otal. This is joint work with Shinpei Baba (Osaka Univ.).

https://u-tokyo-ac-jp.zoom.us/meeting/register/tJUpcOCppzwpGd3r_XqdszQ1XN6FvXpNURbj

#### Operator Algebra Seminars

16:45-18:15 Online

Boundary and rigidity of nonsingular Bernoulli actions

[ Reference URL ]

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

**Yusuke Isono**(RIMS, Kyoto Univ.)Boundary and rigidity of nonsingular Bernoulli actions

[ Reference URL ]

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

### 2021/04/19

#### Seminar on Geometric Complex Analysis

10:30-12:00 Online

カスプと有理同値 (Japanese)

https://u-tokyo-ac-jp.zoom.us/meeting/register/tJ0vcu2rrDIqG9Rv5AT0Mpi37urIkJ1IRldB

**Shouhei Ma**(Tokyo Institute of Technology)カスプと有理同値 (Japanese)

[ Abstract ]

標題の「カスプ」とはいわゆるモジュラー多様体の（ベイリー・ボレル）コンパクト化の境界成分のことである。

1970年代にマニンとドリンフェルトは合同モジュラー曲線の２つのカスプの差がピカール群において有限位数であることを発見した。

代数サイクルの観点からこの現象の高次元版をいくつか古典的な系列のモジュラー多様体の（ベイリー・ボレル、トロイダル）コンパクト化に対して調べたので、それについて報告する。

[ Reference URL ]標題の「カスプ」とはいわゆるモジュラー多様体の（ベイリー・ボレル）コンパクト化の境界成分のことである。

1970年代にマニンとドリンフェルトは合同モジュラー曲線の２つのカスプの差がピカール群において有限位数であることを発見した。

代数サイクルの観点からこの現象の高次元版をいくつか古典的な系列のモジュラー多様体の（ベイリー・ボレル、トロイダル）コンパクト化に対して調べたので、それについて報告する。

https://u-tokyo-ac-jp.zoom.us/meeting/register/tJ0vcu2rrDIqG9Rv5AT0Mpi37urIkJ1IRldB

### 2021/04/15

#### Applied Analysis

### 2021/04/14

#### Algebraic Geometry Seminar

15:00-16:00 Room #Zoom (Graduate School of Math. Sci. Bldg.)

Arithmetic deformation of F-singularities (日本語)

**Kenta Sato**(Kyushu)Arithmetic deformation of F-singularities (日本語)

[ Abstract ]

None

None

### 2021/04/13

#### Tuesday Seminar on Topology

17:00-18:00 Online

Pre-registration required. See our seminar webpage.

Quantitative Birman-Menasco theorem and applications to crossing number (JAPANESE)

https://u-tokyo-ac-jp.zoom.us/meeting/register/tJUpcOCppzwpGd3r_XqdszQ1XN6FvXpNURbj

Pre-registration required. See our seminar webpage.

**Tetsuya Ito**(Kyoto University)Quantitative Birman-Menasco theorem and applications to crossing number (JAPANESE)

[ Abstract ]

Birman-Menasco proved that there are finitely many knots having a given genus and braid index. We give a quantitative version of Birman-Menasco finiteness theorem; an estimate of the crossing number of knots in terms of genus and braid index. As applications, we give various supporting evidences of various conjectural properties of the crossing number of knots.

[ Reference URL ]Birman-Menasco proved that there are finitely many knots having a given genus and braid index. We give a quantitative version of Birman-Menasco finiteness theorem; an estimate of the crossing number of knots in terms of genus and braid index. As applications, we give various supporting evidences of various conjectural properties of the crossing number of knots.

https://u-tokyo-ac-jp.zoom.us/meeting/register/tJUpcOCppzwpGd3r_XqdszQ1XN6FvXpNURbj

#### Operator Algebra Seminars

16:45-18:15 Online

On central sequence algebras of tracial von Neumann algebras

[ Reference URL ]

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

**Yasuhito Hashiba**(Univ. Tokyo)On central sequence algebras of tracial von Neumann algebras

[ Reference URL ]

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

### 2021/04/08

#### Tokyo-Nagoya Algebra Seminar

16:00-17:30 Online

Please see the URL below for details on the online seminar.

Abelian envelopes of monoidal categories (English)

http://www.math.nagoya-u.ac.jp/~aaron.chan/TNAseminar.html

Please see the URL below for details on the online seminar.

**Kevin Coulembier**(Univeristy of Sydney)Abelian envelopes of monoidal categories (English)

[ Abstract ]

For the purposes of this talk, a ‘tensor category’ is an abelian rigid monoidal category, linear over some field. I will try to argue that there are good reasons (inspired by classification attempts of tensor categories, by motives, by Frobenius twists on tensor categories and by the idea of universal tensor categories), to try to associate tensor categories to non-abelian rigid monoidal categories. Then I will comment on some of the recent progress made on such constructions (in work of Benson, Comes, Entova, Etingof, Heidersdof, Hinich, Ostrik, Serganova and myself).

[ Reference URL ]For the purposes of this talk, a ‘tensor category’ is an abelian rigid monoidal category, linear over some field. I will try to argue that there are good reasons (inspired by classification attempts of tensor categories, by motives, by Frobenius twists on tensor categories and by the idea of universal tensor categories), to try to associate tensor categories to non-abelian rigid monoidal categories. Then I will comment on some of the recent progress made on such constructions (in work of Benson, Comes, Entova, Etingof, Heidersdof, Hinich, Ostrik, Serganova and myself).

http://www.math.nagoya-u.ac.jp/~aaron.chan/TNAseminar.html

### 2021/04/06

#### Operator Algebra Seminars

16:45-18:15 Online

Finite Dimensional Approximations of Spectral Triples on Quantum tori (English)

[ Reference URL ]

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

**Frederic Latremoliere**(Univ. Denver)Finite Dimensional Approximations of Spectral Triples on Quantum tori (English)

[ Reference URL ]

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

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