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Future seminars
Seminar information archive ～10/14｜Today's seminar 10/15 | Future seminars 10/16～
2026/10/16
Algebraic Geometry Seminar
13:15-14:45 Room #118 (Graduate School of Math. Sci. Bldg.)
Yutaro Naito (Nagoya University)
Symmetries of toric varieties over fields of characteristic zero
Yutaro Naito (Nagoya University)
Symmetries of toric varieties over fields of characteristic zero
Colloquium
15:30-16:30 Room #NISSAY Lecture Hall (Graduate School of Math. Sci. Bldg.)
Kouichi Taira (Graduate School of Mathematical Sciences, The University of Tokyo)
Spectral theory for the d'Alembertian on Lorentzian manifolds (日本語)
Kouichi Taira (Graduate School of Mathematical Sciences, The University of Tokyo)
Spectral theory for the d'Alembertian on Lorentzian manifolds (日本語)
[ Abstract ]
The spectrum of a linear operator on a Hilbert space may be regarded as an infinite-dimensional generalization of the notion of eigenvalues of matrices, and it has been studied extensively from the viewpoints of analysis and geometry. For example, the spectra of the Laplacian and Dirac operators on Riemannian manifolds are closely related to a variety of geometric phenomena.
Classical results include Weyl's law, which describes the asymptotic behavior of eigenvalues in terms of geometric quantities such as the volume of the manifold, and the index theorem, which relates the zero modes of the Dirac operator to characteristic classes of the manifold. These topics continue to be actively studied today.
On Lorentzian manifolds, which provide the geometric framework for relativity, the spectra of operators such as the d'Alembertian and the Dirac operator have also begun to attract increasing attention in recent years, partly because of applications to quantum theory. In contrast to the Riemannian setting, however, these differential operators are not elliptic, and many of the standard methods are therefore no longer directly applicable. As a result, even fundamental questions such as self-adjointness can be highly nontrivial.
In this talk, I will give an overview of known results on the spectra of differential operators on Riemannian and Lorentzian manifolds and, time permitting, present some of my own results.
The spectrum of a linear operator on a Hilbert space may be regarded as an infinite-dimensional generalization of the notion of eigenvalues of matrices, and it has been studied extensively from the viewpoints of analysis and geometry. For example, the spectra of the Laplacian and Dirac operators on Riemannian manifolds are closely related to a variety of geometric phenomena.
Classical results include Weyl's law, which describes the asymptotic behavior of eigenvalues in terms of geometric quantities such as the volume of the manifold, and the index theorem, which relates the zero modes of the Dirac operator to characteristic classes of the manifold. These topics continue to be actively studied today.
On Lorentzian manifolds, which provide the geometric framework for relativity, the spectra of operators such as the d'Alembertian and the Dirac operator have also begun to attract increasing attention in recent years, partly because of applications to quantum theory. In contrast to the Riemannian setting, however, these differential operators are not elliptic, and many of the standard methods are therefore no longer directly applicable. As a result, even fundamental questions such as self-adjointness can be highly nontrivial.
In this talk, I will give an overview of known results on the spectra of differential operators on Riemannian and Lorentzian manifolds and, time permitting, present some of my own results.
Seminar on Probability and Statistics
15:00-16:00 Room #128 (Graduate School of Math. Sci. Bldg.)
Krzysztof Bartoszek (Department of Computer and Information Science, Linköping University)
An introduction to quadratic stochastic operators (English)
https://u-tokyo-ac-jp.zoom.us/meeting/register/JjtHEBHOT6m4SvmAcXrtWQ
Krzysztof Bartoszek (Department of Computer and Information Science, Linköping University)
An introduction to quadratic stochastic operators (English)
[ Abstract ]
Markov chains are inherently linear processes and also are not elegant for describing interactions between agents. For this end, non-linear models are needed, and quadratic stochastic operators (QSOs) are a first step. They describe mixing of two populations, e.g., sexual reproduction, where one parent comes from the female class and the other from the male class. Studying the law, even in the limit, of a population evolving under a QSO is a challenging task due to the interaction component between the two classes of individuals. Restricting the class of QSOs, to the so-called centred quadratic stochastic operators, one is able to show that, in the case of hermaphroditic species, when the offspring's trait is equal to an additively perturbed arithmetic mean of the parents' traits, one can represent the law of the trait in descendant populations through an appropriate sum of independent random variables. QSOs can be further generalized to an arbitrary number of parents, and cubic stochastic operators are the next step.
[ Reference URL ]Markov chains are inherently linear processes and also are not elegant for describing interactions between agents. For this end, non-linear models are needed, and quadratic stochastic operators (QSOs) are a first step. They describe mixing of two populations, e.g., sexual reproduction, where one parent comes from the female class and the other from the male class. Studying the law, even in the limit, of a population evolving under a QSO is a challenging task due to the interaction component between the two classes of individuals. Restricting the class of QSOs, to the so-called centred quadratic stochastic operators, one is able to show that, in the case of hermaphroditic species, when the offspring's trait is equal to an additively perturbed arithmetic mean of the parents' traits, one can represent the law of the trait in descendant populations through an appropriate sum of independent random variables. QSOs can be further generalized to an arbitrary number of parents, and cubic stochastic operators are the next step.
https://u-tokyo-ac-jp.zoom.us/meeting/register/JjtHEBHOT6m4SvmAcXrtWQ
2026/10/19
Operator Algebra Seminars
15:30-17:00 Room # 126 (Graduate School of Math. Sci. Bldg.)
Xin-Hai Tong (The University of Tokyo)
Clustering Theorem for Bose--Hubbard class Gibbs states
Xin-Hai Tong (The University of Tokyo)
Clustering Theorem for Bose--Hubbard class Gibbs states
Seminar on Geometric Complex Analysis
10:30-12:00 Room #126 (Graduate School of Math. Sci. Bldg.)
Ryota Kotani (Institute of Science Tokyo)
A Torelli-type theorem for hyperkähler quotients (Japanese)
[ Reference URL ]
https://forms.gle/8ERsVDLuKHwbVzm57
Ryota Kotani (Institute of Science Tokyo)
A Torelli-type theorem for hyperkähler quotients (Japanese)
[ Reference URL ]
https://forms.gle/8ERsVDLuKHwbVzm57
Tokyo Probability Seminar
16:00-17:30 Room #122 (Graduate School of Math. Sci. Bldg.)
We are having teatime from 15:20 in the common room on the second floor. Please join us.
Kohki Sakamoto (The University of Tokyo)
Singularity of harmonic measure on Poisson-Voronoi tessellations in hyperbolic spaces
We are having teatime from 15:20 in the common room on the second floor. Please join us.
Kohki Sakamoto (The University of Tokyo)
Singularity of harmonic measure on Poisson-Voronoi tessellations in hyperbolic spaces
[ Abstract ]
Poisson-Voronoi tessellations provide natural examples of invariant random tilings of homogeneous spaces. Benjamini, Paquette, and Pfeffer proved that the nearest-neighbor random walk on the Poisson-Voronoi tessellation of the hyperbolic plane has positive drift and hence converges to the boundary circle. They further conjectured that its hitting measure on the boundary is singular with respect to Lebesgue measure. I will explain how this follows from an ergodic-theoretic argument based on rerooting relations, and briefly discuss the higher-dimensional case as well.
Poisson-Voronoi tessellations provide natural examples of invariant random tilings of homogeneous spaces. Benjamini, Paquette, and Pfeffer proved that the nearest-neighbor random walk on the Poisson-Voronoi tessellation of the hyperbolic plane has positive drift and hence converges to the boundary circle. They further conjectured that its hitting measure on the boundary is singular with respect to Lebesgue measure. I will explain how this follows from an ergodic-theoretic argument based on rerooting relations, and briefly discuss the higher-dimensional case as well.
2026/10/20
Tuesday Seminar on Topology
17:30-18:30 Room #hybrid/056 (Graduate School of Math. Sci. Bldg.)
Pre-registration required. See our seminar webpage.
Ken’ichi Ohshika (Gakushuin University)
Structures of unit tangent spheres of Thurston’s metric (JAPANESE)
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html
Pre-registration required. See our seminar webpage.
Ken’ichi Ohshika (Gakushuin University)
Structures of unit tangent spheres of Thurston’s metric (JAPANESE)
[ Abstract ]
Thurston introduced in the 1980s a new metric on Teichmüller space using best Lipschitz maps instead of best quasi-conformal maps. Thurston’s metric is Finsler, and so we can consider the associated norm on tangent spaces of Teichmüller space. In this talk, we show how the unit sphere of this norm looks, regarded as a convex sphere. We in particular give a formula for dimensions of faces. This is a part of joint work with A. Papadopoulos.
[ Reference URL ]Thurston introduced in the 1980s a new metric on Teichmüller space using best Lipschitz maps instead of best quasi-conformal maps. Thurston’s metric is Finsler, and so we can consider the associated norm on tangent spaces of Teichmüller space. In this talk, we show how the unit sphere of this norm looks, regarded as a convex sphere. We in particular give a formula for dimensions of faces. This is a part of joint work with A. Papadopoulos.
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html
2026/10/23
Algebraic Geometry Seminar
13:15-14:45 Room #118 (Graduate School of Math. Sci. Bldg.)
Matthias Schütt (Leibniz Univ. Hannover)
Real, Complex and Salem multiplication for K3 surfaces
Matthias Schütt (Leibniz Univ. Hannover)
Real, Complex and Salem multiplication for K3 surfaces
[ Abstract ]
TBA
TBA
2026/10/26
Seminar on Geometric Complex Analysis
10:30-12:00 Room #126 (Graduate School of Math. Sci. Bldg.)
Takayuki Koike (Univ. of Tsukuba)
Rigidity of pseudoconvex neighborhoods on Ueda-type examples
(Japanese)
[ Reference URL ]
https://forms.gle/8ERsVDLuKHwbVzm57
Takayuki Koike (Univ. of Tsukuba)
Rigidity of pseudoconvex neighborhoods on Ueda-type examples
(Japanese)
[ Reference URL ]
https://forms.gle/8ERsVDLuKHwbVzm57
Operator Algebra Seminars
15:30-17:00 Room # 126 (Graduate School of Math. Sci. Bldg.)
Miho Mukohara (Kyushu University )
C*-discrete inclusions and approximations by finite-index bimodules
Miho Mukohara (Kyushu University )
C*-discrete inclusions and approximations by finite-index bimodules
2026/11/02
Operator Algebra Seminars
15:30-17:00 Room # 126 (Graduate School of Math. Sci. Bldg.)
Michiya Mori (Niigata University)
Isometries between C*-algebras with finite corank
Michiya Mori (Niigata University)
Isometries between C*-algebras with finite corank
[ Abstract ]
In this talk, we give a characterization of linear isometries with finite corank between two arbitrary unital C*-algebras in terms of Jordan *-homomorphisms and “finite-dimensional remainders”. Also, the corresponding results are given for linear isometries and linear order embeddings between self-adjoint parts of C*-algebras. In the finite-dimensional case, we give new examples of linear isometries between matrix algebras. This talk is based on arXiv:2607.13367.
In this talk, we give a characterization of linear isometries with finite corank between two arbitrary unital C*-algebras in terms of Jordan *-homomorphisms and “finite-dimensional remainders”. Also, the corresponding results are given for linear isometries and linear order embeddings between self-adjoint parts of C*-algebras. In the finite-dimensional case, we give new examples of linear isometries between matrix algebras. This talk is based on arXiv:2607.13367.
Seminar on Geometric Complex Analysis
10:30-12:00 Room #126 (Graduate School of Math. Sci. Bldg.)
Masakazu Takakura (Tokyo Metropolitan Univ.)
(Japanese)
https://forms.gle/8ERsVDLuKHwbVzm57
Masakazu Takakura (Tokyo Metropolitan Univ.)
(Japanese)
[ Abstract ]
[ Reference URL ]https://forms.gle/8ERsVDLuKHwbVzm57
2026/11/06
Algebraic Geometry Seminar
13:15-14:45 Room #118 (Graduate School of Math. Sci. Bldg.)
Shu Nimura (Nagoya University)
TBA
Shu Nimura (Nagoya University)
TBA
[ Abstract ]
TBA
TBA
2026/11/09
Operator Algebra Seminars
15:30-17:00 Room # 126 (Graduate School of Math. Sci. Bldg.)
Hikaru Sekiyama (Keio University)
KS-Groupoids and KS-Crossed Products associated with Inverse Semigroup Actions
Hikaru Sekiyama (Keio University)
KS-Groupoids and KS-Crossed Products associated with Inverse Semigroup Actions
Seminar on Geometric Complex Analysis
10:30-12:00 Room #126 (Graduate School of Math. Sci. Bldg.)
Junjiro Noguchi (The Univ. of Tokyo)
(Japanese)
https://forms.gle/8ERsVDLuKHwbVzm57
Junjiro Noguchi (The Univ. of Tokyo)
(Japanese)
[ Abstract ]
[ Reference URL ]https://forms.gle/8ERsVDLuKHwbVzm57
Tokyo Probability Seminar
16:00-17:30 Room #122 (Graduate School of Math. Sci. Bldg.)
We are having teatime from 15:20 in the common room on the second floor. Please join us.
Kenta Misumi (The University of Tokyo)
ディリクレ空間で、準至る所ベクトル束を作り、マルコフ過程に沿って準至る所ベクトルを平行移動する。
We are having teatime from 15:20 in the common room on the second floor. Please join us.
Kenta Misumi (The University of Tokyo)
ディリクレ空間で、準至る所ベクトル束を作り、マルコフ過程に沿って準至る所ベクトルを平行移動する。
[ Abstract ]
準正則 Dirichlet 空間上において準ベクトル束の概念を定式化することにより、その分類量として第一 Stiefel–Whitney 類が自然に現れる。さらに、この枠組みに適合する接続の理論を公理的に構築することで、対応する右過程の軌道に沿ったベクトルの準至る所での平行移動を構成することが可能となる。
この構成は、従来の Riemann 多様体あるいは sub-Riemann 多様体上の Brown 運動に沿う確率平行移動を包含するだけでなく、一般のジャンプ型過程に沿う確率平行移動も含む。さらには、RCD 空間など、特異空間上の Brown 運動に沿う確率平行移動さえも導く。
したがって本理論は、滑らかさに依存していた従来の平行移動の概念を、準正則 Dirichlet 形式と右過程を基礎とする非滑らかな対象へ拡張する一般的な枠組みを与えるものとなる。
準正則 Dirichlet 空間上において準ベクトル束の概念を定式化することにより、その分類量として第一 Stiefel–Whitney 類が自然に現れる。さらに、この枠組みに適合する接続の理論を公理的に構築することで、対応する右過程の軌道に沿ったベクトルの準至る所での平行移動を構成することが可能となる。
この構成は、従来の Riemann 多様体あるいは sub-Riemann 多様体上の Brown 運動に沿う確率平行移動を包含するだけでなく、一般のジャンプ型過程に沿う確率平行移動も含む。さらには、RCD 空間など、特異空間上の Brown 運動に沿う確率平行移動さえも導く。
したがって本理論は、滑らかさに依存していた従来の平行移動の概念を、準正則 Dirichlet 形式と右過程を基礎とする非滑らかな対象へ拡張する一般的な枠組みを与えるものとなる。
2026/11/10
Numerical Analysis Seminar
16:30-18:00 Room #122 (Graduate School of Math. Sci. Bldg.)
Takiko Sasaki (Musashino University)
TBA (Japanese)
[ Reference URL ]
https://sites.google.com/g.ecc.u-tokyo.ac.jp/utnas-bulletin-board/
Takiko Sasaki (Musashino University)
TBA (Japanese)
[ Reference URL ]
https://sites.google.com/g.ecc.u-tokyo.ac.jp/utnas-bulletin-board/
2026/11/16
Operator Algebra Seminars
15:30-17:00 Room # 126 (Graduate School of Math. Sci. Bldg.)
Kohki Sakamoto (The University of Tokyo)
TBA
Kohki Sakamoto (The University of Tokyo)
TBA
2026/11/17
Numerical Analysis Seminar
16:30-18:00 Room #122 (Graduate School of Math. Sci. Bldg.)
Kazunori Matsui (Tokyo University of Marine Science and Technology)
A projection method for a visco-elasto-plasticity model with linear kinematic hardening and its vanishing viscosity limit (Japanese)
[ Reference URL ]
https://sites.google.com/g.ecc.u-tokyo.ac.jp/utnas-bulletin-board/
Kazunori Matsui (Tokyo University of Marine Science and Technology)
A projection method for a visco-elasto-plasticity model with linear kinematic hardening and its vanishing viscosity limit (Japanese)
[ Reference URL ]
https://sites.google.com/g.ecc.u-tokyo.ac.jp/utnas-bulletin-board/
2026/11/20
Seminar on Mathematics for various disciplines
14:00-15:00 Room #056 (Graduate School of Math. Sci. Bldg.)
This seminar is held on Friday afternoon.
Dieter Bothe (Technische Universität Darmstadt)
Multicomponent Diffusion — Modelling and Analysis (English)
This seminar is held on Friday afternoon.
Dieter Bothe (Technische Universität Darmstadt)
Multicomponent Diffusion — Modelling and Analysis (English)
[ Abstract ]
Diffusion in fluid systems composed of several chemical species is a classical subject with a surprisingly rich mathematical structure. In contrast to scalar diffusion, the motion of the individual components is coupled through conservation laws, thermodynamic constraints, and interspecies interactions. This leads to strongly coupled systems of nonlinear partial differential equations, whose modelling and analysis are closely intertwined. The talk introduces the main ideas of multicomponent diffusion, from its physical and thermodynamic foundations to modern mathematical formulations. Particular emphasis is placed on the relation between physically meaningful constitutive laws and the qualitative properties of the resulting PDE systems, including the question of global regularity for large data.
Diffusion in fluid systems composed of several chemical species is a classical subject with a surprisingly rich mathematical structure. In contrast to scalar diffusion, the motion of the individual components is coupled through conservation laws, thermodynamic constraints, and interspecies interactions. This leads to strongly coupled systems of nonlinear partial differential equations, whose modelling and analysis are closely intertwined. The talk introduces the main ideas of multicomponent diffusion, from its physical and thermodynamic foundations to modern mathematical formulations. Particular emphasis is placed on the relation between physically meaningful constitutive laws and the qualitative properties of the resulting PDE systems, including the question of global regularity for large data.
2026/11/30
Operator Algebra Seminars
15:30-17:00 Room #126 (Graduate School of Math. Sci. Bldg.)
Fuyuta Komura (Kyushu Institute of Technology)
Cartan-preserving *-automorphism groups: realization and obstructions for compact abelian groups
Fuyuta Komura (Kyushu Institute of Technology)
Cartan-preserving *-automorphism groups: realization and obstructions for compact abelian groups
[ Abstract ]
In this talk, we investigate automorphism groups preserving Cartan subalgebras of C*-algebras. First, we describe these groups in terms of automorphisms and 1-cocycles of twisted étale groupoids. As a consequence, we obtain a C*-algebraic analogue of a theorem of Feldman and Moore on Cartan-preserving automorphisms of von Neumann algebras. We then study Cartan-fixing automorphism groups. We show that every UCT Kirchberg algebra admits a Cartan subalgebra whose Cartan-fixing automorphism group contains every second countable compact abelian group. In contrast, for C*-algebras arising from expansive effective groupoids, we prove that compact Cartan-fixing automorphism groups must have finitely generated Pontryagin duals if the fixed point subalgebras are prime. As an application, we establish the existence of inequivalent Cartan subalgebras for Kirchberg algebras arising from expansive effective groupoids.
In this talk, we investigate automorphism groups preserving Cartan subalgebras of C*-algebras. First, we describe these groups in terms of automorphisms and 1-cocycles of twisted étale groupoids. As a consequence, we obtain a C*-algebraic analogue of a theorem of Feldman and Moore on Cartan-preserving automorphisms of von Neumann algebras. We then study Cartan-fixing automorphism groups. We show that every UCT Kirchberg algebra admits a Cartan subalgebra whose Cartan-fixing automorphism group contains every second countable compact abelian group. In contrast, for C*-algebras arising from expansive effective groupoids, we prove that compact Cartan-fixing automorphism groups must have finitely generated Pontryagin duals if the fixed point subalgebras are prime. As an application, we establish the existence of inequivalent Cartan subalgebras for Kirchberg algebras arising from expansive effective groupoids.
2026/12/07
Operator Algebra Seminars
15:30-17:00 Room # 126 (Graduate School of Math. Sci. Bldg.)
Akihiro Miyagawa (Kyoto University)
TBA
Akihiro Miyagawa (Kyoto University)
TBA
2026/12/11
Algebraic Geometry Seminar
13:15-14:45 Room #118 (Graduate School of Math. Sci. Bldg.)
Yutaro Hiroi (University of Osaka)
TBA
Yutaro Hiroi (University of Osaka)
TBA
[ Abstract ]
TBA
TBA
2026/12/14
Operator Algebra Seminars
15:30-17:00 Room # 126 (Graduate School of Math. Sci. Bldg.)
Yuki Arano (Nagoya University)
Prime actions of compact groups on von Neumann algebras
Yuki Arano (Nagoya University)
Prime actions of compact groups on von Neumann algebras
2027/01/18
Operator Algebra Seminars
15:30-17:00 Room # 126 (Graduate School of Math. Sci. Bldg.)
Katsunori Fujie (Aichi Prefectural University)
TBA
Katsunori Fujie (Aichi Prefectural University)
TBA
