Text only print
Full screen print
Future seminars
Seminar information archive ～09/24｜Today's seminar 09/25 | Future seminars 09/26～
2026/09/28
Tokyo Probability Seminar
14:00-17:30 Room #126 (Graduate School of Math. Sci. Bldg.)
We are having teatime from 15:20 in the common room on the second floor. Please join us.
Stefan Junk ( Gakushuin University) 14:00-15:15
Some elements of the proof of equivalence of strong and very strong disorder for directed polymers (private seminar)
Dominik Schmid ( University of Augsburg) 16:00-17:30
The periodic directed landscape
We are having teatime from 15:20 in the common room on the second floor. Please join us.
Stefan Junk ( Gakushuin University) 14:00-15:15
Some elements of the proof of equivalence of strong and very strong disorder for directed polymers (private seminar)
Dominik Schmid ( University of Augsburg) 16:00-17:30
The periodic directed landscape
[ Abstract ]
The Kardar--Parisi--Zhang universality class is a central topic in mathematical physics and probability theory. In this talk, we discuss the conjectural scaling limit of periodic models in the Kardar--Parisi--Zhang universality class: the periodic directed landscape. We establish the convergence of periodic exponential last passage percolation to the periodic directed landscape and give a variational characterization of the periodic KPZ fixed point, recently constructed by Baik, Liao, and Liu. We also establish the convergence of periodic asymmetric simple exclusion processes to periodic KPZ fixed points, coupled through the same periodic directed landscape. A key ingredient is a gluing technique for combining overlapping directed landscapes, which may be of independent interest. This is based on joint work with Amol Aggarwal and Ivan Corwin.
The Kardar--Parisi--Zhang universality class is a central topic in mathematical physics and probability theory. In this talk, we discuss the conjectural scaling limit of periodic models in the Kardar--Parisi--Zhang universality class: the periodic directed landscape. We establish the convergence of periodic exponential last passage percolation to the periodic directed landscape and give a variational characterization of the periodic KPZ fixed point, recently constructed by Baik, Liao, and Liu. We also establish the convergence of periodic asymmetric simple exclusion processes to periodic KPZ fixed points, coupled through the same periodic directed landscape. A key ingredient is a gluing technique for combining overlapping directed landscapes, which may be of independent interest. This is based on joint work with Amol Aggarwal and Ivan Corwin.
2026/10/02
Algebraic Geometry Seminar
10:30-12:00 Room #122 (Graduate School of Math. Sci. Bldg.)
JongHae Keum (KIAS)
Automorphisms of Fermat quartic surface
JongHae Keum (KIAS)
Automorphisms of Fermat quartic surface
[ Abstract ]
In 1944 Beniamino Segre proved that the Fermat quartic surface in the 3-dimensional projective space has infinitely many discrete automorphisms. It was the first example of an algebraic surface with infinite discrete automorphism group. Since then, it has long been an open problem to find generators of its automorphism group.
On the other hand, any other Fermat hypersurface of dimension > 1 and degree > 2 admits only projectively linear automorphisms, and has finite automorphism group.
With Keiji Oguiso and Xun Yu, we solve this problem, finding 16 geometric generators of finite order.
I will present this result, along with history of computation of automorphism groups of other K3 surfaces.
In 1944 Beniamino Segre proved that the Fermat quartic surface in the 3-dimensional projective space has infinitely many discrete automorphisms. It was the first example of an algebraic surface with infinite discrete automorphism group. Since then, it has long been an open problem to find generators of its automorphism group.
On the other hand, any other Fermat hypersurface of dimension > 1 and degree > 2 admits only projectively linear automorphisms, and has finite automorphism group.
With Keiji Oguiso and Xun Yu, we solve this problem, finding 16 geometric generators of finite order.
I will present this result, along with history of computation of automorphism groups of other K3 surfaces.
2026/10/05
Operator Algebra Seminars
15:30-17:00 Room # 126 (Graduate School of Math. Sci. Bldg.)
Takehiko Mori (Salesian Polytechnic)
The qx+r problem and the Cuntz algebra
Takehiko Mori (Salesian Polytechnic)
The qx+r problem and the Cuntz algebra
Seminar on Geometric Complex Analysis
10:30-12:00 Room #126 (Graduate School of Math. Sci. Bldg.)
Tomoyuki Hisamoto (Nagoya Univ.)
Miyaoka–Yau inequality, delta invariant, and the Calabi functional (Japanese)
[ Reference URL ]
https://forms.gle/8ERsVDLuKHwbVzm57
Tomoyuki Hisamoto (Nagoya Univ.)
Miyaoka–Yau inequality, delta invariant, and the Calabi functional (Japanese)
[ Reference URL ]
https://forms.gle/8ERsVDLuKHwbVzm57
Tokyo Probability Seminar
16:50-18:20 Room #122 (Graduate School of Math. Sci. Bldg.)
The classroom is 122. No Tea Time today.
Dai Taguchi (Kansai University)
Euler–Maruyama scheme with unbounded Hölder drift
The classroom is 122. No Tea Time today.
Dai Taguchi (Kansai University)
Euler–Maruyama scheme with unbounded Hölder drift
[ Abstract ]
In this talk, we establish the strong rate of convergence of the Euler--Maruyama scheme for multidimensional stochastic differential equations with unbounded, uniformly locally Hölder continuous drift and multiplicative noise. Our approach relies on the Itô--Tanaka trick (Zvonkin-type transformation) adapted to unbounded drift. Furthermore, in order to apply the stochastic sewing lemma, we employ heat kernel estimates for the transition density of the Euler--Maruyama scheme. This talk is based on joint work with Tsukasa Moritoki (Okayama university).
In this talk, we establish the strong rate of convergence of the Euler--Maruyama scheme for multidimensional stochastic differential equations with unbounded, uniformly locally Hölder continuous drift and multiplicative noise. Our approach relies on the Itô--Tanaka trick (Zvonkin-type transformation) adapted to unbounded drift. Furthermore, in order to apply the stochastic sewing lemma, we employ heat kernel estimates for the transition density of the Euler--Maruyama scheme. This talk is based on joint work with Tsukasa Moritoki (Okayama university).
2026/10/06
Numerical Analysis Seminar
16:30-18:00 Room #002 (Graduate School of Math. Sci. Bldg.)
Yohance Osborne (Durham University)
Numerical approximation of mean field games systems (English)
https://sites.google.com/g.ecc.u-tokyo.ac.jp/utnas-bulletin-board/
Yohance Osborne (Durham University)
Numerical approximation of mean field games systems (English)
[ Abstract ]
Mean field games (MFG) are models for Nash equilibria of competitive differential games of optimal control involving a continuum of players. MFG equilibria are often described by systems of partial differential equations, where a Hamilton–Jacobi–Bellman (HJB) equation for the representative player’s value function is coupled nonlinearly with a Kolmogorov–Fokker–Planck (KFP) equation that determines the player distribution. MFG systems are particularly challenging to approximate computationally because they exhibit the following difficulties all at once: nonlinear couplings between the HJB and KFP equations, a temporal forward–backward structure, non-negativity of absolutely continuous player distributions, as well as potential nondifferentiability of the Hamiltonian. This talk addresses the numerical approximation of MFG systems for two classes of numerical schemes: (1) monotone stabilized finite element methods for second-order MFG systems with nondifferentiable Hamiltonians, and (2) particle methods for first-order MFG systems under displacement monotonicity. I will present theorems on the strong convergence of these numerical schemes and their rates of convergence, along with discussion of some numerical experiments.
[ Reference URL ]Mean field games (MFG) are models for Nash equilibria of competitive differential games of optimal control involving a continuum of players. MFG equilibria are often described by systems of partial differential equations, where a Hamilton–Jacobi–Bellman (HJB) equation for the representative player’s value function is coupled nonlinearly with a Kolmogorov–Fokker–Planck (KFP) equation that determines the player distribution. MFG systems are particularly challenging to approximate computationally because they exhibit the following difficulties all at once: nonlinear couplings between the HJB and KFP equations, a temporal forward–backward structure, non-negativity of absolutely continuous player distributions, as well as potential nondifferentiability of the Hamiltonian. This talk addresses the numerical approximation of MFG systems for two classes of numerical schemes: (1) monotone stabilized finite element methods for second-order MFG systems with nondifferentiable Hamiltonians, and (2) particle methods for first-order MFG systems under displacement monotonicity. I will present theorems on the strong convergence of these numerical schemes and their rates of convergence, along with discussion of some numerical experiments.
https://sites.google.com/g.ecc.u-tokyo.ac.jp/utnas-bulletin-board/
Tuesday Seminar on Topology
16:00-17:30 Room #hybrid/056 (Graduate School of Math. Sci. Bldg.)
Pre-registration required. See our seminar webpage.
Kouichi Taira (Kyushu University)
Large eigenvalues and logarithmic Weyl law of the Connes-Moscovici operator (JAPANESE)
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html
Pre-registration required. See our seminar webpage.
Kouichi Taira (Kyushu University)
Large eigenvalues and logarithmic Weyl law of the Connes-Moscovici operator (JAPANESE)
[ Abstract ]
The Bohr-Sommerfeld quantization condition is a principle that describes the semiclassical eigenvalues of a quantum system in terms of action integrals along closed trajectories of the corresponding classical system. A refined quantization condition incorporating the Maslov index as a correction term was independently discovered by Keller and Maslov, and a mathematically rigorous framework was subsequently developed by Arnold and Hörmander. On the other hand, for one-dimensional Sturm-Liouville systems under suitable boundary conditions, it may give rise to discrete eigenvalues even in situations where the usual Bohr-Sommerfeld picture based on closed classical trajectories does not directly apply. In this talk, we focus on the prolate operator recently introduced by Connes and Moscovici, and explain how eigenvalues arise when the corresponding classical system has no closed trajectories, as well as how these eigenvalues can be related to action integrals and Maslov index. As an application, we present a result concerning a Weyl law with a logarithmic term, conjectured by Connes and Moscovici, which describes the asymptotic behavior of the eigenvalue counting function. This is a joint work with M. Willems(Utrecht University) and M.Wrochna (Utrecht University).
[ Reference URL ]The Bohr-Sommerfeld quantization condition is a principle that describes the semiclassical eigenvalues of a quantum system in terms of action integrals along closed trajectories of the corresponding classical system. A refined quantization condition incorporating the Maslov index as a correction term was independently discovered by Keller and Maslov, and a mathematically rigorous framework was subsequently developed by Arnold and Hörmander. On the other hand, for one-dimensional Sturm-Liouville systems under suitable boundary conditions, it may give rise to discrete eigenvalues even in situations where the usual Bohr-Sommerfeld picture based on closed classical trajectories does not directly apply. In this talk, we focus on the prolate operator recently introduced by Connes and Moscovici, and explain how eigenvalues arise when the corresponding classical system has no closed trajectories, as well as how these eigenvalues can be related to action integrals and Maslov index. As an application, we present a result concerning a Weyl law with a logarithmic term, conjectured by Connes and Moscovici, which describes the asymptotic behavior of the eigenvalue counting function. This is a joint work with M. Willems(Utrecht University) and M.Wrochna (Utrecht University).
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html
2026/10/08
Numerical Analysis Seminar
16:30-18:00 Room #002 (Graduate School of Math. Sci. Bldg.)
Note that the seminar will be held on Thursday.
Marcus Grote (University of Basel)
Adaptive FEM with Explicit Time Integration For the Wave Equation
(English)
https://sites.google.com/g.ecc.u-tokyo.ac.jp/utnas-bulletin-board/
Note that the seminar will be held on Thursday.
Marcus Grote (University of Basel)
Adaptive FEM with Explicit Time Integration For the Wave Equation
(English)
[ Abstract ]
Starting from a recent a posteriori error estimator for the finite element solution of the wave equation with explicit time integration [Grote, Lakkis, Santos, 2024], we devise a space-time adaptive strategy which includes both time evolving meshes and local time-stepping to overcome any overly stringent CFL stability restriction on the time-step due to local mesh refinement. Moreover, at each time-step the adaptive algorithm monitors the accuracy thanks to the error indicators and recomputes the current step on a refined mesh until the desired tolerance is met; meanwhile, the mesh is coarsened in regions of smaller errors. Leapfrog based local time-stepping is applied in all regions of local mesh refinement to incorporate adaptivity into fully explicit time integration with mesh change while retaining efficiency. Numerical results illustrate the optimal rate of convergence of the a posteriori error estimators on time evolving meshes.
[ Reference URL ]Starting from a recent a posteriori error estimator for the finite element solution of the wave equation with explicit time integration [Grote, Lakkis, Santos, 2024], we devise a space-time adaptive strategy which includes both time evolving meshes and local time-stepping to overcome any overly stringent CFL stability restriction on the time-step due to local mesh refinement. Moreover, at each time-step the adaptive algorithm monitors the accuracy thanks to the error indicators and recomputes the current step on a refined mesh until the desired tolerance is met; meanwhile, the mesh is coarsened in regions of smaller errors. Leapfrog based local time-stepping is applied in all regions of local mesh refinement to incorporate adaptivity into fully explicit time integration with mesh change while retaining efficiency. Numerical results illustrate the optimal rate of convergence of the a posteriori error estimators on time evolving meshes.
https://sites.google.com/g.ecc.u-tokyo.ac.jp/utnas-bulletin-board/
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)
. (Japanese)
[ Reference URL ]
https://forms.gle/8ERsVDLuKHwbVzm57
Ryota Kotani (Institute of Science Tokyo)
. (Japanese)
[ Reference URL ]
https://forms.gle/8ERsVDLuKHwbVzm57
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)
(Japanese)
[ Reference URL ]
https://forms.gle/8ERsVDLuKHwbVzm57
Takayuki Koike (Univ. of Tsukuba)
(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 )
TBA
Miho Mukohara (Kyushu University )
TBA
2026/11/02
Operator Algebra Seminars
15:30-17:00 Room # 126 (Graduate School of Math. Sci. Bldg.)
Michiya Mori (Niigata University)
TBA
Michiya Mori (Niigata University)
TBA
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
2026/11/09
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
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
2026/11/30
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
2026/12/14
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
