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Seminar information archive
Seminar information archive ～06/05｜Today's seminar 06/06 | Future seminars 06/07～
2026/06/05
Algebraic Geometry Seminar
14:00-15:00 Room #大講義室（NISSAY Lecture Hall） (Graduate School of Math. Sci. Bldg.)
Young-Hoon Kiem (Korea Institute for Advanced Study)
Cohomology of moduli spaces of curves
Young-Hoon Kiem (Korea Institute for Advanced Study)
Cohomology of moduli spaces of curves
[ Abstract ]
Moduli spaces of stable pointed curves have been much studied but still we know surprisingly little about their cohomology. In this talk, I will discuss some recent progresses based on techniques from combinatorics and probability theory as well as the algebraic geometry of wall crossings in the stack of maps.
Moduli spaces of stable pointed curves have been much studied but still we know surprisingly little about their cohomology. In this talk, I will discuss some recent progresses based on techniques from combinatorics and probability theory as well as the algebraic geometry of wall crossings in the stack of maps.
2026/06/04
Applied Analysis
16:00-17:30 Room # 002 (Graduate School of Math. Sci. Bldg.)
Shobu Shiraki (University of Zagreb)
Beckner's sharp inequalities revisited on binary cubes (Japanese)
Shobu Shiraki (University of Zagreb)
Beckner's sharp inequalities revisited on binary cubes (Japanese)
[ Abstract ]
The Hausdorff–Young inequality and Young’s convolution inequality are fundamental tools in harmonic analysis. The landmark paper “Inequalities in Fourier Analysis” by William Beckner (Ann. of Math., 1975) established the exact values of the sharp constants appearing in these inequalities. Recently, these inequalities have received renewed attention in the setting of binary cubes, driven by applications in additive combinatorics through works by Kane–Tao, de Dios Pont–Greenfeld–Ivanisvili–Madrid, and others. In this discrete setting, the sharp constant is known to be 1 and is no longer the central issue. Instead, the focus shifts to the range of exponents for which the Hausdorff–Young inequality and Young’s convolution inequality hold — a range that is enlarged compared to the classical case. In this talk, we aim to fully characterize this range. This is joint work with Tonći Crmarić (University of Split) and Vjekoslav Kovač (University of Zagreb).
The Hausdorff–Young inequality and Young’s convolution inequality are fundamental tools in harmonic analysis. The landmark paper “Inequalities in Fourier Analysis” by William Beckner (Ann. of Math., 1975) established the exact values of the sharp constants appearing in these inequalities. Recently, these inequalities have received renewed attention in the setting of binary cubes, driven by applications in additive combinatorics through works by Kane–Tao, de Dios Pont–Greenfeld–Ivanisvili–Madrid, and others. In this discrete setting, the sharp constant is known to be 1 and is no longer the central issue. Instead, the focus shifts to the range of exponents for which the Hausdorff–Young inequality and Young’s convolution inequality hold — a range that is enlarged compared to the classical case. In this talk, we aim to fully characterize this range. This is joint work with Tonći Crmarić (University of Split) and Vjekoslav Kovač (University of Zagreb).
2026/06/02
Operator Algebra Seminars
16:45-18:15 Room #126 (Graduate School of Math. Sci. Bldg.)
Yusuke Nishinaka (Osaka Metropolitan Univ.)
Costello-Gwilliam factorization algebras and vertex algebras
[ Reference URL ]
https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm
Yusuke Nishinaka (Osaka Metropolitan Univ.)
Costello-Gwilliam factorization algebras and vertex algebras
[ Reference URL ]
https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm
FJ-LMI Seminar
10:00-12:00 Room # (Graduate School of Math. Sci. Bldg.)
Makiko SASADA (The University of Tokyo)
Scaling Limits of Interacting Particle Systems: From Gaussian Fields to KPZ Universality
https://fj-lmi.cnrs.fr/fj-lmi-day-2026/
Makiko SASADA (The University of Tokyo)
Scaling Limits of Interacting Particle Systems: From Gaussian Fields to KPZ Universality
[ Abstract ]
This talk explores the scaling limits of interacting particle systems with multiple conserved quantities. Starting from weakly asymmetric dynamics on a lattice, we characterize the evolution of fluctuation fields in the diffusive limit. We show how the interplay between different conserved modes leads to a transition from linear Gaussian fields to the KPZ (Kardar-Parisi-Zhang) universality class. Using the framework of Nonlinear Fluctuating Hydrodynamics, we discuss how the second-order nonlinearities in the macroscopic currents determine whether each mode exhibits diffusive or anomalous scaling. This talk is based on joint work with Hugo Da Cunha.
[ Reference URL ]This talk explores the scaling limits of interacting particle systems with multiple conserved quantities. Starting from weakly asymmetric dynamics on a lattice, we characterize the evolution of fluctuation fields in the diffusive limit. We show how the interplay between different conserved modes leads to a transition from linear Gaussian fields to the KPZ (Kardar-Parisi-Zhang) universality class. Using the framework of Nonlinear Fluctuating Hydrodynamics, we discuss how the second-order nonlinearities in the macroscopic currents determine whether each mode exhibits diffusive or anomalous scaling. This talk is based on joint work with Hugo Da Cunha.
https://fj-lmi.cnrs.fr/fj-lmi-day-2026/
FJ-LMI Seminar
10:00-12:00 Room # (Graduate School of Math. Sci. Bldg.)
Takeshi SAITO (The University of Tokyo)
Some developments in cohomology theories in arithmetic (英語)
https://fj-lmi.cnrs.fr/fj-lmi-day-2026/
Takeshi SAITO (The University of Tokyo)
Some developments in cohomology theories in arithmetic (英語)
[ Abstract ]
The introduction of cohomology theories into arithmetic geometry has its roots in the Weil conjectures and began with Grothendieck’s definition of étale cohomology in the 1960s. We will discuss several more recent developments, particularly those arising from collaborations between French and Japanese mathematicians, including motives with modulus, $p$-adic Simpson correspondences, and analogies with microlocal analysis.
[ Reference URL ]The introduction of cohomology theories into arithmetic geometry has its roots in the Weil conjectures and began with Grothendieck’s definition of étale cohomology in the 1960s. We will discuss several more recent developments, particularly those arising from collaborations between French and Japanese mathematicians, including motives with modulus, $p$-adic Simpson correspondences, and analogies with microlocal analysis.
https://fj-lmi.cnrs.fr/fj-lmi-day-2026/
FJ-LMI Seminar
10:00-12:00 Room # (Graduate School of Math. Sci. Bldg.)
Luc PIRIO (CNRS FJ-LMI)
Lines, Curves, Surfaces, and Functional Equations
https://fj-lmi.cnrs.fr/fj-lmi-day-2026/
Luc PIRIO (CNRS FJ-LMI)
Lines, Curves, Surfaces, and Functional Equations
[ Abstract ]
This short talk will offer an informal and visual introduction to families of curves on surfaces, and explain how these geometric objects naturally lead to an interesting class of functional equations.
[ Reference URL ]This short talk will offer an informal and visual introduction to families of curves on surfaces, and explain how these geometric objects naturally lead to an interesting class of functional equations.
https://fj-lmi.cnrs.fr/fj-lmi-day-2026/
FJ-LMI Seminar
10:00-12:00 Room # (Graduate School of Math. Sci. Bldg.)
Valentin MASSICOT (CNRS FJ-LMI (IRL2025) & LMR (UMR 9008))
Double quotients for symmetry breaking
https://fj-lmi.cnrs.fr/fj-lmi-day-2026/
Valentin MASSICOT (CNRS FJ-LMI (IRL2025) & LMR (UMR 9008))
Double quotients for symmetry breaking
[ Abstract ]
The orbit structure in flag varieties encodes branching laws for real reductive groups. In this talk, we describe a family of double quotients which arise naturally in the context of symmetry breaking for the general linear group.
These spaces generalize certain classical quotients, a fundamental example being the one associated with Gaussian elimination and the Bruhat decomposition. In this setting, double cosets are described using natural invariants inspired by the ranks of submatrices in the classical case.
[ Reference URL ]The orbit structure in flag varieties encodes branching laws for real reductive groups. In this talk, we describe a family of double quotients which arise naturally in the context of symmetry breaking for the general linear group.
These spaces generalize certain classical quotients, a fundamental example being the one associated with Gaussian elimination and the Bruhat decomposition. In this setting, double cosets are described using natural invariants inspired by the ranks of submatrices in the classical case.
https://fj-lmi.cnrs.fr/fj-lmi-day-2026/
Numerical Analysis Seminar
16:30-18:00 Room #002 (Graduate School of Math. Sci. Bldg.)
Mikhail Lavrentiev (Novosibirsk State University and Institute of Automation & Electrometry SB RAS)
Fast numerical solution to shallow water system at PC - application to tsunami simulation (English)
https://sites.google.com/g.ecc.u-tokyo.ac.jp/utnas-bulletin-board/
Mikhail Lavrentiev (Novosibirsk State University and Institute of Automation & Electrometry SB RAS)
Fast numerical solution to shallow water system at PC - application to tsunami simulation (English)
[ Abstract ]
To calculate the distribution of maximal tsunami wave heights along the shoreline immediately after the earthquake a number of algorithms have been developed. Due to the hardware acceleration (the use of FPGA - Field Programmable Gates Array - microchip) numerical solution to the shallow water system takes 1 minute with Personal Computer within 1000x600 km water area, grid step compared to 250 m.
It takes 25 min to compute wave propagation over the entire Pacific Ocean at 1 min grid. Using the advantages of FPGA architecture, values of wave parameters are calculated at 7 time layers at one computer clock. The propores technology could be applied for more problems in computational hydrodynamics.
[ Reference URL ]To calculate the distribution of maximal tsunami wave heights along the shoreline immediately after the earthquake a number of algorithms have been developed. Due to the hardware acceleration (the use of FPGA - Field Programmable Gates Array - microchip) numerical solution to the shallow water system takes 1 minute with Personal Computer within 1000x600 km water area, grid step compared to 250 m.
It takes 25 min to compute wave propagation over the entire Pacific Ocean at 1 min grid. Using the advantages of FPGA architecture, values of wave parameters are calculated at 7 time layers at one computer clock. The propores technology could be applied for more problems in computational hydrodynamics.
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.
Tomohiro Asano (Kyoto University)
Knot types of Lagrangian intersections and epimorphisms between knot groups (JAPANESE)
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html
Pre-registration required. See our seminar webpage.
Tomohiro Asano (Kyoto University)
Knot types of Lagrangian intersections and epimorphisms between knot groups (JAPANESE)
[ Abstract ]
Lagrangian intersections in symplectic manifolds have been studied from various perspectives. In recent years, several works have also investigated the knot types of Lagrangian intersections.
In this talk, we discuss a problem posed by Okamoto. Starting from a knot in the 3-dimensional Euclidean space, we move its conormal bundle in the cotangent bundle by a compactly supported Hamiltonian isotopy. When its intersection with the zero-section is connected and clean, it gives rise to another knot. We ask how the knot type of this new knot is related to that of the original one.
I will explain a new constraint on this problem obtained by using microlocal sheaf theory, in terms of the fundamental groups of knot complements. This talk is based on joint work with Yukihiro Okamoto (Tokyo Metropolitan University).
[ Reference URL ]Lagrangian intersections in symplectic manifolds have been studied from various perspectives. In recent years, several works have also investigated the knot types of Lagrangian intersections.
In this talk, we discuss a problem posed by Okamoto. Starting from a knot in the 3-dimensional Euclidean space, we move its conormal bundle in the cotangent bundle by a compactly supported Hamiltonian isotopy. When its intersection with the zero-section is connected and clean, it gives rise to another knot. We ask how the knot type of this new knot is related to that of the original one.
I will explain a new constraint on this problem obtained by using microlocal sheaf theory, in terms of the fundamental groups of knot complements. This talk is based on joint work with Yukihiro Okamoto (Tokyo Metropolitan University).
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html
FJ-LMI Seminar
10:00-12:00 Room # (Graduate School of Math. Sci. Bldg.)
Toshiyuki Kobayashi (The University of Tokyo)
Symmetry Breaking and Geometric Analysis
https://fj-lmi.cnrs.fr/fj-lmi-day-2026/
Toshiyuki Kobayashi (The University of Tokyo)
Symmetry Breaking and Geometric Analysis
[ Abstract ]
In this talk, I first give a brief overview of fundamental problems in the branching theory of infinite-dimensional representations, namely the study of restricted representations. I then discuss recent advances in this area and their applications to spectral analysis on locally symmetric spaces beyond the traditional Riemannian setting, with particular emphasis on joint work with French colleagues.
[ Reference URL ]In this talk, I first give a brief overview of fundamental problems in the branching theory of infinite-dimensional representations, namely the study of restricted representations. I then discuss recent advances in this area and their applications to spectral analysis on locally symmetric spaces beyond the traditional Riemannian setting, with particular emphasis on joint work with French colleagues.
https://fj-lmi.cnrs.fr/fj-lmi-day-2026/
2026/06/01
Seminar on Geometric Complex Analysis
10:30-12:00 Room #126 (Graduate School of Math. Sci. Bldg.)
Yohei Komori (Waseda Univ.)
Classification of arithmetic twice-punctured torus groups (Japanese)
https://forms.gle/8ERsVDLuKHwbVzm57
Yohei Komori (Waseda Univ.)
Classification of arithmetic twice-punctured torus groups (Japanese)
[ Abstract ]
A Fuchsian group is called arithmetic if it is commensurable with a Fuchsian group derived from a quaternion algebra. In this talk we will determine arithmetic twice-punctured torus groups; arithmetic once-punctured torus groups were already classified by Kisao Takeuchi. Our strategy is based on Takeuchi's approach to classify quadrilateral subgroups of the modular group. (“Subgroups of the modular group with signature (0 ; e1, e2, e3, e4)”（Saitama Math. Jour. Vol.14, 55—78, 1996).)
[ Reference URL ]A Fuchsian group is called arithmetic if it is commensurable with a Fuchsian group derived from a quaternion algebra. In this talk we will determine arithmetic twice-punctured torus groups; arithmetic once-punctured torus groups were already classified by Kisao Takeuchi. Our strategy is based on Takeuchi's approach to classify quadrilateral subgroups of the modular group. (“Subgroups of the modular group with signature (0 ; e1, e2, e3, e4)”（Saitama Math. Jour. Vol.14, 55—78, 1996).)
https://forms.gle/8ERsVDLuKHwbVzm57
2026/05/29
Algebraic Geometry Seminar
13:15-14:45 Room #117 (Graduate School of Math. Sci. Bldg.)
Yuki Koto (Academia Sinica)
Towards a quantization of the Kirwan map via Fourier transform
Yuki Koto (Academia Sinica)
Towards a quantization of the Kirwan map via Fourier transform
[ Abstract ]
Quantum cohomology ring is a deformation of the ordinary cohomology ring defined using counts of rational curves (genus zero Gromov-Witten invariants). In this talk, I will propose a Fourier transform for the quantum cohomology of smooth projective GIT quotients, viewed as a quantum analogue of the Kirwan map in ordinary cohomology. I will present several examples where this Fourier transform can be constructed and discuss some applications. This talk is based on ongoing work.
Quantum cohomology ring is a deformation of the ordinary cohomology ring defined using counts of rational curves (genus zero Gromov-Witten invariants). In this talk, I will propose a Fourier transform for the quantum cohomology of smooth projective GIT quotients, viewed as a quantum analogue of the Kirwan map in ordinary cohomology. I will present several examples where this Fourier transform can be constructed and discuss some applications. This talk is based on ongoing work.
2026/05/27
Number Theory Seminar
17:00-18:00 Room #117 (Graduate School of Math. Sci. Bldg.)
ONISHI Haruto (University of Tokyo)
Geometric realization of the local Langlands and local Jacquet-Langlands correspondences for GL(4) in a partially ramified case
ONISHI Haruto (University of Tokyo)
Geometric realization of the local Langlands and local Jacquet-Langlands correspondences for GL(4) in a partially ramified case
[ Abstract ]
The local Langlands correspondence and the local Jacquet-Langlands correspondence are realized using Lubin-Tate spaces. However, only limited cases of the correspondence between supercuspidal representations and L-parameters have been geometrically realized by algebraic varieties defined by explicit equations. There are several works in which such algebraic varieties are obtained as reductions of special affinoids in the Lubin-Tate space at infinite level. Even in the essentially tame case, where the correspondence is explicitly described by Bushnell–Henniart, such affinoids had previously been constructed only in the unramified and totally ramified cases. In this talk, I will explain a result constructing such affinoids in a partially ramified case, under certain special assumptions.
The local Langlands correspondence and the local Jacquet-Langlands correspondence are realized using Lubin-Tate spaces. However, only limited cases of the correspondence between supercuspidal representations and L-parameters have been geometrically realized by algebraic varieties defined by explicit equations. There are several works in which such algebraic varieties are obtained as reductions of special affinoids in the Lubin-Tate space at infinite level. Even in the essentially tame case, where the correspondence is explicitly described by Bushnell–Henniart, such affinoids had previously been constructed only in the unramified and totally ramified cases. In this talk, I will explain a result constructing such affinoids in a partially ramified case, under certain special assumptions.
Tokyo-Nagoya Algebra Seminar
16:00-17:30 Online
Yuki Mizuno (Utrecht University)
Bondal–Orlov’s reconstruction theorem in noncommutative projective geometry (Japanese)
http://www.math.nagoya-u.ac.jp/~aaron.chan/TNAseminar.html
Yuki Mizuno (Utrecht University)
Bondal–Orlov’s reconstruction theorem in noncommutative projective geometry (Japanese)
[ Abstract ]
The (derived) category of coherent sheaves on a scheme encodes rich
information about the underlying geometry. P. Gabriel showed that for
noetherian schemes X and Y, if Coh X and Coh Y are equivalent as abelian
categories, then X and Y are isomorphic. Furthermore, A. Bondal and D.
Orlov proved that for smooth projective schemes X and Y with
(anti-)ample canonical bundles, if D^b(Coh X) and D^b(Coh Y) are
equivalent as triangulated categories, then X and Y are isomorphic. On
the other hand, J.-P. Serre showed that the category of coherent sheaves
on a projective scheme can be described as the quotient category of
finitely generated graded modules over the homogeneous coordinate ring
by the subcategory of torsion modules. Motivated by the results of
Gabriel and Serre, the quotient category of finitely generated graded
modules over a (not necessarily commutative) graded ring by the
subcategory of torsion modules is called a noncommutative projective scheme.
In this talk, I will present an analogue of Bondal–Orlov’s
reconstruction theorem for noncommutative projective geometry.
Furthermore, if time permits, I will discuss recent progress on the
study of the derived autoequivalence groups of noncommutative projective
schemes. Specifically, I will mention a structure result for the derived
autoequivalence groups of certain noncommutative projective planes.
ミーティング ID: 828 6882 8074
パスコード: 131261
[ Reference URL ]The (derived) category of coherent sheaves on a scheme encodes rich
information about the underlying geometry. P. Gabriel showed that for
noetherian schemes X and Y, if Coh X and Coh Y are equivalent as abelian
categories, then X and Y are isomorphic. Furthermore, A. Bondal and D.
Orlov proved that for smooth projective schemes X and Y with
(anti-)ample canonical bundles, if D^b(Coh X) and D^b(Coh Y) are
equivalent as triangulated categories, then X and Y are isomorphic. On
the other hand, J.-P. Serre showed that the category of coherent sheaves
on a projective scheme can be described as the quotient category of
finitely generated graded modules over the homogeneous coordinate ring
by the subcategory of torsion modules. Motivated by the results of
Gabriel and Serre, the quotient category of finitely generated graded
modules over a (not necessarily commutative) graded ring by the
subcategory of torsion modules is called a noncommutative projective scheme.
In this talk, I will present an analogue of Bondal–Orlov’s
reconstruction theorem for noncommutative projective geometry.
Furthermore, if time permits, I will discuss recent progress on the
study of the derived autoequivalence groups of noncommutative projective
schemes. Specifically, I will mention a structure result for the derived
autoequivalence groups of certain noncommutative projective planes.
ミーティング ID: 828 6882 8074
パスコード: 131261
http://www.math.nagoya-u.ac.jp/~aaron.chan/TNAseminar.html
2026/05/26
Operator Algebra Seminars
16:45-18:15 Room #126 (Graduate School of Math. Sci. Bldg.)
Takumi Nishihara (RIMS, Kyoto Univ.)
Compact group actions and $G$-kernels on von Neumann algebras
[ Reference URL ]
https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar-e.htm
Takumi Nishihara (RIMS, Kyoto Univ.)
Compact group actions and $G$-kernels on von Neumann algebras
[ Reference URL ]
https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar-e.htm
Numerical Analysis Seminar
16:30-18:00 Room #002 (Graduate School of Math. Sci. Bldg.)
Qin(Tim) Sheng (Baylor University)
Advances in Splitting: Intercardinal Approaches to Nonlinear Hideo Kawarada Equations
(English)
https://sites.google.com/g.ecc.u-tokyo.ac.jp/utnas-bulletin-board/
Qin(Tim) Sheng (Baylor University)
Advances in Splitting: Intercardinal Approaches to Nonlinear Hideo Kawarada Equations
(English)
[ Abstract ]
This presentation addresses two main issues. First, we shall discuss recent advancements in both exponential and non-exponential splitting methods, with particular emphasis on their stability, accuracy and global error estimates. Second, we shall introduce a new splitting configuration for solving nonlinear Hideo Kawarada equations with mixed derivative terms. This approach leads to intercardinal splitting finite-difference schemes that provide efficient and accurate numerical approximations of the underlying solutions.
We shall further demonstrate that the resulting implicit methods are numerically stable, convergent, and efficient, while preserving key physical properties such as the positivity and monotonicity. The dynamic orders of accuracy of the proposed algorithms will be illustrated using generalized Milne devices. Simulation examples of the solution procedure will be presented and investigated, and several open problems will also be outlined.
[ Reference URL ]This presentation addresses two main issues. First, we shall discuss recent advancements in both exponential and non-exponential splitting methods, with particular emphasis on their stability, accuracy and global error estimates. Second, we shall introduce a new splitting configuration for solving nonlinear Hideo Kawarada equations with mixed derivative terms. This approach leads to intercardinal splitting finite-difference schemes that provide efficient and accurate numerical approximations of the underlying solutions.
We shall further demonstrate that the resulting implicit methods are numerically stable, convergent, and efficient, while preserving key physical properties such as the positivity and monotonicity. The dynamic orders of accuracy of the proposed algorithms will be illustrated using generalized Milne devices. Simulation examples of the solution procedure will be presented and investigated, and several open problems will also be outlined.
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.
Kento Sakai (The University of Tokyo)
On the large-scale geometry of k-multicurve graphs (JAPANESE)
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html
Pre-registration required. See our seminar webpage.
Kento Sakai (The University of Tokyo)
On the large-scale geometry of k-multicurve graphs (JAPANESE)
[ Abstract ]
Graphs whose vertices are isotopy classes of simple closed curves, or multicurves, on surfaces have been widely studied, since they admit natural actions of mapping class groups. The curve graph and the pants graph are two fundamental examples. These graphs have found many applications in low-dimensional topology, including the study of Teichmüller spaces, Kleinian groups, and topology of 3-manifolds. In particular, the Gromov hyperbolicity of the curve graph, established by Masur and Minsky, played an important role in the proof of the Ending Lamination Theorem.
The k-multicurve graph, introduced by Erlandsson and Fanoni, is a graph whose vertices are multicurves with k components. It provides a natural interpolation between the curve graph and the pants graph. In this talk, we will present results on large-scale geometric properties of k-multicurve graphs, including hyperbolicity, relative hyperbolicity, and quasi-flat rank. If time permits, we will also discuss some connections with mapping class groups and Teichmüller spaces. This talk is based on joint work with Erika Kuno (Shibaura Institute of Technology) and Rin Kuramochi (The University of Tokyo).
[ Reference URL ]Graphs whose vertices are isotopy classes of simple closed curves, or multicurves, on surfaces have been widely studied, since they admit natural actions of mapping class groups. The curve graph and the pants graph are two fundamental examples. These graphs have found many applications in low-dimensional topology, including the study of Teichmüller spaces, Kleinian groups, and topology of 3-manifolds. In particular, the Gromov hyperbolicity of the curve graph, established by Masur and Minsky, played an important role in the proof of the Ending Lamination Theorem.
The k-multicurve graph, introduced by Erlandsson and Fanoni, is a graph whose vertices are multicurves with k components. It provides a natural interpolation between the curve graph and the pants graph. In this talk, we will present results on large-scale geometric properties of k-multicurve graphs, including hyperbolicity, relative hyperbolicity, and quasi-flat rank. If time permits, we will also discuss some connections with mapping class groups and Teichmüller spaces. This talk is based on joint work with Erika Kuno (Shibaura Institute of Technology) and Rin Kuramochi (The University of Tokyo).
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html
Lie Groups and Representation Theory
16:00-17:00 Room #128 (Graduate School of Math. Sci. Bldg.)
Víctor Pérez-Valdés (The University of Tokyo)
On sporadic symmetry breaking operators from $S^3$ to $S^2$
Víctor Pérez-Valdés (The University of Tokyo)
On sporadic symmetry breaking operators from $S^3$ to $S^2$
[ Abstract ]
In this talk we construct and classify all differential symmetry breaking operators between certain principal series representations of the pair $(SO_0(4,1), SO_0(3,1))$.
In this case, we also prove a localness theorem, namely, all symmetry breaking operators between the principal series representations in concern are necessarily differential operators.
In addition, we show that all these symmetry breaking operators are sporadic, that is, they cannot be obtained by residue formulas of meromorphic families of symmetry breaking operators.
In this talk we construct and classify all differential symmetry breaking operators between certain principal series representations of the pair $(SO_0(4,1), SO_0(3,1))$.
In this case, we also prove a localness theorem, namely, all symmetry breaking operators between the principal series representations in concern are necessarily differential operators.
In addition, we show that all these symmetry breaking operators are sporadic, that is, they cannot be obtained by residue formulas of meromorphic families of symmetry breaking operators.
2026/05/25
Seminar on Geometric Complex Analysis
10:30-12:00 Room #126 (Graduate School of Math. Sci. Bldg.)
Misa Ohashi (Nagoya Institute of Technology)
Geometric structures on Hirzebruch surfaces from the viewpoint of $S^{3} \times S^{3}$ (Japanese)
https://forms.gle/8ERsVDLuKHwbVzm57
Misa Ohashi (Nagoya Institute of Technology)
Geometric structures on Hirzebruch surfaces from the viewpoint of $S^{3} \times S^{3}$ (Japanese)
[ Abstract ]
For a non-negative integer $m$, each Hirzebruch surface Wm is defined as a complex two-dimensional K\"ahler submanifold of the product of the complex projective line and the complex projective plane. It is known that Hirzebruch surfaces are all biregularly distinct. The purpose of this talk is to describe the complex structures on Hirzebruch surfaces from a differential geometric point of view. For each $m$, we show that the real two-dimensional torus bundle over a Hirzebruch surface is diffeomorphic to the product of two 3-spheres, $S^{3} \times S^{3}$. From this, we realize the complex structure as a global section (tensor field) on $S^{3} \times S^{3}$. We explain the construction of these diffeomorphisms and their properties. This talk is based on joint work with Hideya Hashimoto.
[ Reference URL ]For a non-negative integer $m$, each Hirzebruch surface Wm is defined as a complex two-dimensional K\"ahler submanifold of the product of the complex projective line and the complex projective plane. It is known that Hirzebruch surfaces are all biregularly distinct. The purpose of this talk is to describe the complex structures on Hirzebruch surfaces from a differential geometric point of view. For each $m$, we show that the real two-dimensional torus bundle over a Hirzebruch surface is diffeomorphic to the product of two 3-spheres, $S^{3} \times S^{3}$. From this, we realize the complex structure as a global section (tensor field) on $S^{3} \times S^{3}$. We explain the construction of these diffeomorphisms and their properties. This talk is based on joint work with Hideya Hashimoto.
https://forms.gle/8ERsVDLuKHwbVzm57
Tokyo Probability Seminar
16:00-17:30 Room #126 (Graduate School of Math. Sci. Bldg.)
We are having teatime from 15:15 in the common room on the second floor. Please join us.
Fumiya Okazaki (Science Tokyo)
非局所ディリクレ形式に関する調和写像の微分に付随する接束上のマルチンゲールについて
We are having teatime from 15:15 in the common room on the second floor. Please join us.
Fumiya Okazaki (Science Tokyo)
非局所ディリクレ形式に関する調和写像の微分に付随する接束上のマルチンゲールについて
[ Abstract ]
リーマン多様体が高次のユークリッド空間に埋め込まれているという仮定の下では, その多様体に値を取る非局所ディリクレ形式に関する調和写像を変分原理に基づいて定義できる. 例えば分数冪ラプラシアンに関するディリクレ形式を考えた場合は, Da Lio-Rivière (2011)で導入された分数冪ラプラシアンに関する調和写像に対応する. 本研究では値域の多様体の幾何と調和写像の関係を見ることを目的として, 調和写像にある程度の正則性を課し, その微分を確率過程を通して考察する. まず接束上の不連続なセミマルチンゲールに対する伊藤解析を, 第2基本形式などを用いてジャンプを定めることで定式化し, それを用いて接束上の不連続なマルチンゲールを導入する. また写像の定義域の空間として別のリーマン多様体と, その上のあるKillingベクトル場による変換で不変なディリクレ形式を考え, そのKillingベクトル場による調和写像の微分から定まるジャンプ過程が接束上のマルチンゲールとなることを紹介する.
リーマン多様体が高次のユークリッド空間に埋め込まれているという仮定の下では, その多様体に値を取る非局所ディリクレ形式に関する調和写像を変分原理に基づいて定義できる. 例えば分数冪ラプラシアンに関するディリクレ形式を考えた場合は, Da Lio-Rivière (2011)で導入された分数冪ラプラシアンに関する調和写像に対応する. 本研究では値域の多様体の幾何と調和写像の関係を見ることを目的として, 調和写像にある程度の正則性を課し, その微分を確率過程を通して考察する. まず接束上の不連続なセミマルチンゲールに対する伊藤解析を, 第2基本形式などを用いてジャンプを定めることで定式化し, それを用いて接束上の不連続なマルチンゲールを導入する. また写像の定義域の空間として別のリーマン多様体と, その上のあるKillingベクトル場による変換で不変なディリクレ形式を考え, そのKillingベクトル場による調和写像の微分から定まるジャンプ過程が接束上のマルチンゲールとなることを紹介する.
2026/05/22
Algebraic Geometry Seminar
13:15-14:45 Room #117 (Graduate School of Math. Sci. Bldg.)
Justin Sawon (University of North Carolina Chapel Hill)
Classification results for Lagrangian fibrations
Justin Sawon (University of North Carolina Chapel Hill)
Classification results for Lagrangian fibrations
[ Abstract ]
A Lagrangian fibration on a holomorphic symplectic manifold or variety is one whose general fibre is an abelian variety that is Lagrangian with respect to the symplectic form. Examples were constructed by Beauville/Mukai whose fibres are Jacobians of curves, and by Markushevich-Tikhomirov, Arbarella-Sacca-Ferretti, Matteini, S-Shen, and Brakkee-Camere-Grossi-Pertusi-Sacca-Viktorova whose fibres are Prym varieties of curves with involutions. In all of these examples the family of curves is a linear system on a K3 surface, suggesting the question: is this always the case? Markushevich answered this affirmatively in the genus two case: if the relative compactified Jacobian of a family of genus two curves is a Lagrangian fibration then the curves all lie on a K3 surface, and the Lagrangian fibration is a Beauville-Mukai system. In this talk I will describe our generalization of this result to higher genus, and also to relative Prym varieties of genus three covers with involutions (joint work with Xuqiang Qin).
A Lagrangian fibration on a holomorphic symplectic manifold or variety is one whose general fibre is an abelian variety that is Lagrangian with respect to the symplectic form. Examples were constructed by Beauville/Mukai whose fibres are Jacobians of curves, and by Markushevich-Tikhomirov, Arbarella-Sacca-Ferretti, Matteini, S-Shen, and Brakkee-Camere-Grossi-Pertusi-Sacca-Viktorova whose fibres are Prym varieties of curves with involutions. In all of these examples the family of curves is a linear system on a K3 surface, suggesting the question: is this always the case? Markushevich answered this affirmatively in the genus two case: if the relative compactified Jacobian of a family of genus two curves is a Lagrangian fibration then the curves all lie on a K3 surface, and the Lagrangian fibration is a Beauville-Mukai system. In this talk I will describe our generalization of this result to higher genus, and also to relative Prym varieties of genus three covers with involutions (joint work with Xuqiang Qin).
Colloquium
15:30-16:30 Room #NISSAY Lecture Hall (Graduate School of Math. Sci. Bldg.)
Evgeny Shinder (University of Sheffield / University of Tokyo)
Gromov's cancellation question in birational algebraic geometry
Evgeny Shinder (University of Sheffield / University of Tokyo)
Gromov's cancellation question in birational algebraic geometry
[ Abstract ]
Gromov's 1999 cancellation question is: given two open embeddings of a variety U into a variety X, do they always have isomorphic closed complements? In my joint work with Hsueh-Yung Lin we reformulate this question in terms of the structure of the Grothendieck ring of varieties and answer it in various situations. The answer will be positive or negative depending on the dimension of varieties and the ground field. Finally, I will present an application to the structure of the Cremona group of birational self-maps of the projective space.
Gromov's 1999 cancellation question is: given two open embeddings of a variety U into a variety X, do they always have isomorphic closed complements? In my joint work with Hsueh-Yung Lin we reformulate this question in terms of the structure of the Grothendieck ring of varieties and answer it in various situations. The answer will be positive or negative depending on the dimension of varieties and the ground field. Finally, I will present an application to the structure of the Cremona group of birational self-maps of the projective space.
2026/05/21
FJ-LMI Seminar
14:15-15:00 Room # (Graduate School of Math. Sci. Bldg.)
Julien ROUYER (École Centrale de Pékin, Beihang university, Beijing)
How to cross an intersection ?
Julien ROUYER (École Centrale de Pékin, Beihang university, Beijing)
How to cross an intersection ?
[ Abstract ]
Under certain constraints, we enumerate the different ways of simultaneously crossing a road intersection with alternating entries and exits, for a maximal number of vehicles. The problem reduces to the study of various types of non-crossing partitions of {1,…,n} and gives rise to new integer sequences. Standard combinatorial methods then lead to systems of polynomial equations, in which the unknowns are the generating functions of these sequences.
Under certain constraints, we enumerate the different ways of simultaneously crossing a road intersection with alternating entries and exits, for a maximal number of vehicles. The problem reduces to the study of various types of non-crossing partitions of {1,…,n} and gives rise to new integer sequences. Standard combinatorial methods then lead to systems of polynomial equations, in which the unknowns are the generating functions of these sequences.
2026/05/20
Number Theory Seminar
17:00-18:00 Room #117 (Graduate School of Math. Sci. Bldg.)
Yukako Kezuka (University of Tokyo)
Special values of $L$-functions and the Birch and Swinnerton-Dyer conjecture for CM elliptic curves
https://www.ms.u-tokyo.ac.jp/~kezuka/
Yukako Kezuka (University of Tokyo)
Special values of $L$-functions and the Birch and Swinnerton-Dyer conjecture for CM elliptic curves
[ Abstract ]
Elliptic curves with complex multiplication (CM) have long served as some of the most powerful examples for understanding the Birch and Swinnerton-Dyer (BSD) conjecture. In particular, a wide range of arithmetic phenomena has been observed in families of quadratic twists of these curves. In this talk, I will explain how CM elliptic curves have been used to advance our understanding of the conjecture, and discuss some current directions in this area, focusing in particular on Iwasawa theory and recent developments involving the Gross family of elliptic curves.
[ Reference URL ]Elliptic curves with complex multiplication (CM) have long served as some of the most powerful examples for understanding the Birch and Swinnerton-Dyer (BSD) conjecture. In particular, a wide range of arithmetic phenomena has been observed in families of quadratic twists of these curves. In this talk, I will explain how CM elliptic curves have been used to advance our understanding of the conjecture, and discuss some current directions in this area, focusing in particular on Iwasawa theory and recent developments involving the Gross family of elliptic curves.
https://www.ms.u-tokyo.ac.jp/~kezuka/
Tokyo-Nagoya Algebra Seminar
13:00-14:30 Online
Heizo Sakamoto (University of Tokyo)
アフィン型団代数のモノイダル圏化におけるアフィン量子群の実加群と虚加群の分類 (Japanese)
[ Reference URL ]
https://www.math.nagoya-u.ac.jp/~aaron.chan/TNAseminar.html
Heizo Sakamoto (University of Tokyo)
アフィン型団代数のモノイダル圏化におけるアフィン量子群の実加群と虚加群の分類 (Japanese)
[ Reference URL ]
https://www.math.nagoya-u.ac.jp/~aaron.chan/TNAseminar.html
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