## Seminar information archive

### 2021/04/28

#### Algebraic Geometry Seminar

15:00-16:00   Room #Zoom (Graduate School of Math. Sci. Bldg.)
Tasuki Kinjo (Tokyo/IPMU)
Dimensional reduction in cohomological Donaldson-Thomas theory (日本語)
[ Abstract ]
None

### 2021/04/27

#### Numerical Analysis Seminar

16:30-18:00   Online
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
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.
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 ]
https://u-tokyo-ac-jp.zoom.us/meeting/register/tJUpcOCppzwpGd3r_XqdszQ1XN6FvXpNURbj

### 2021/04/26

#### Seminar on Geometric Complex Analysis

10:30-12:00   Online
Jun O'Hara (Chiba University)

[ 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。

[ Reference URL ]
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.
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 ]
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

#### Information Mathematics Seminar

16:50-18:35   Online
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 ]

### 2021/04/21

#### Algebraic Geometry Seminar

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

#### Seminar on Probability and Statistics

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

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 ]

#### Seminar on Probability and Statistics

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

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 ]

### 2021/04/20

#### Tuesday Seminar on Topology

17:00-18:00   Online
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 ]
https://u-tokyo-ac-jp.zoom.us/meeting/register/tJUpcOCppzwpGd3r_XqdszQ1XN6FvXpNURbj

#### Operator Algebra Seminars

16:45-18:15   Online
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
Shouhei Ma (Tokyo Institute of Technology)
カスプと有理同値 (Japanese)
[ Abstract ]

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。

[ Reference URL ]
https://u-tokyo-ac-jp.zoom.us/meeting/register/tJ0vcu2rrDIqG9Rv5AT0Mpi37urIkJ1IRldB

### 2021/04/15

#### Applied Analysis

16:00-17:30   Online
( )
(Japanese)
[ Reference URL ]
https://forms.gle/61xaUyw6Pk44QVZi9

### 2021/04/14

#### Algebraic Geometry Seminar

15:00-16:00   Room #Zoom (Graduate School of Math. Sci. Bldg.)
Kenta Sato (Kyushu)
Arithmetic deformation of F-singularities (日本語)
[ Abstract ]
None

### 2021/04/13

#### Tuesday Seminar on Topology

17:00-18:00   Online
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 ]
https://u-tokyo-ac-jp.zoom.us/meeting/register/tJUpcOCppzwpGd3r_XqdszQ1XN6FvXpNURbj

#### Operator Algebra Seminars

16:45-18:15   Online
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.
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 ]
http://www.math.nagoya-u.ac.jp/~aaron.chan/TNAseminar.html

### 2021/04/06

#### Operator Algebra Seminars

16:45-18:15   Online
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

### 2021/03/29

#### Seminar on Probability and Statistics

14:00-15:10   Online
Register at least 3 days before at the reference URL. The URL for participation sent before the seminar.
Masaaki Imaizumi (University of Tokyo)
On Gaussian Approximation for M-Estimator (JAPANESE)
[ Abstract ]
This study develops a non-asymptotic Gaussian approximation theory for distributions of M-estimators, which are defined as maximizers of empirical criterion functions. In existing mathematical statistics literature, numerous studies have focused on approximating the distributions of the M-estimators for statistical inference. In contrast to the existing approaches, which mainly focus on limiting behaviors, this study employs a non-asymptotic approach, establishes abstract Gaussian approximation results for maximizers of empirical criteria, and proposes a Gaussian multiplier bootstrap approximation method. Our developments can be considered as extensions of the seminal works on the approximation theory for distributions of suprema of empirical processes toward their maximizers. Through this work, we shed new lights on the statistical theory of M-estimators. Our theory covers not only regular estimators, such as the least absolute deviations, but also some non-regular cases where it is difficult to derive or to approximate numerically the limiting distributions such as non-Donsker classes and cube root estimators.
[ Reference URL ]

### 2021/03/24

#### Seminar on Probability and Statistics

14:30-16:00   Online
Register at least 3 days before at the reference URL. The URL for participation sent before the seminar.
Rachel Fewster (University of Auckland)
Stochastic modelling in ecology: why is it interesting? (ENGLISH)
[ Abstract ]
Asia-Pacific Seminar in Probability and Statistics https://sites.google.com/view/apsps/home

The ecological sciences offer rich pickings for stochastic modellers. There is currently an abundance of new technologies for　monitoring wildlife and biodiversity, for which no practicable data-analysis methods exist. Often, modelling approaches that are motivated by a specific problem with relatively narrow focus can turn out to have　surprisingly broad application elsewhere. As the generality of the problem structure becomes clear, this can also motivate new statistical theory.

I will describe some ecological modelling scenarios that have led to interesting developments from methodological and theoretical perspectives.　As time allows, these will include: saddlepoint approximations for dealing　with data corrupted by non-invertible linear transformations; information theory for assuring that it is a good idea to unite data from multiple sources; and methods for dealing with so-called 'enigmatic' data from remote sensors, involving a blend of ideas from point processes, queuing theory, and trigonometry. All scenarios will be generously illustrated with　pictures of charismatic wildlife.

This talk covers joint work with numerous collaborators, especially Joey Wei Zhang, Mark Bravington, Peter Jupp, Jesse Goodman, Martin Hazelton,　Godrick Oketch, Ben Stevenson, David Borchers, Paul van Dam-Bates, and　Stephen Marsland.
[ Reference URL ]

### 2021/03/19

#### Colloquium

15:00-17:30   Online
Yoshikazu Giga (University of Tokyo) 15:00-16:00
Effects of viscosity and diffusion described by differential equations (JAPANESE)
Toshitake Kohno (Meiji University/University of Tokyo) 16:30-17:30
Monodromy representations in higher categories and iterated integrals (JAPANESE)

#### Lectures

18:00-19:00   Online
Day 3 of a series of three lectures (3/17,18,19)
Matthew Morrow (CNRS, IMJ-PRG)
Progress in syntomic cohomology (ENGLISH)
[ Abstract ]
The talks will present a survey of the (quasi)syntomic cohomology theory introduced by Bhatt, Scholze, and the speaker; this provides a variant of the syntomic cohomology of Fontaine, Kato, and Messing which has the advantage of being defined in a greater degree of generality and working well with torsion coefficients even for small primes. Although it underlies in principle a general theory of p-adic étale motivic cohomology, the talks will probably focus more on arithmetic aspects such as applications in p-adic Hodge theory. Based on various projects joint with Antieau, Bhatt, Clausen, Kelly, Lüders, Mathew, Nikolaus, and Scholze.
[ Reference URL ]
https://www.ms.u-tokyo.ac.jp/~shiho/spparis/index.html

### 2021/03/18

#### Lectures

17:30-18:30   Online
Day 2 of a series of three lectures (3/17,18,19)
Matthew Morrow (CNRS, IMJ-PRG)
Progress in syntomic cohomology (ENGLISH)
[ Abstract ]
The talks will present a survey of the (quasi)syntomic cohomology theory introduced by Bhatt, Scholze, and the speaker; this provides a variant of the syntomic cohomology of Fontaine, Kato, and Messing which has the advantage of being defined in a greater degree of generality and working well with torsion coefficients even for small primes. Although it underlies in principle a general theory of p-adic étale motivic cohomology, the talks will probably focus more on arithmetic aspects such as applications in p-adic Hodge theory. Based on various projects joint with Antieau, Bhatt, Clausen, Kelly, Lüders, Mathew, Nikolaus, and Scholze.
[ Reference URL ]
https://www.ms.u-tokyo.ac.jp/~shiho/spparis/index.html