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Seminar information archive
Seminar information archive ～07/10｜Today's seminar 07/11 | Future seminars 07/12～
2026/07/08
Number Theory Seminar
17:00-18:00 Room #117 (Graduate School of Math. Sci. Bldg.)
Vova Sosnilo (RIKEN iTHEMS)
Descent for algebraic K-theory of algebraic stacks
https://vova-sosnilo.com/
Vova Sosnilo (RIKEN iTHEMS)
Descent for algebraic K-theory of algebraic stacks
[ Abstract ]
Algebraic K-theory satisfies descent with respect to Nisnevich covers, which allows one to deduce global computations for schemes to the affine case. For algebraic stacks this is insufficient, since algebraic stacks with nontrivial stabilizers do not admit Nisnevich covers by affine schemes. However, a theorem of Deshmukh shows that any algebraic stack with separated diagonal admits a Nisnevich surjection from an affine scheme. The Atiyah—Segal completion theorem measures precisely the failure of algebraic K-theory to satisfy descent with respect to Nisnevich surjections. We show that it holds for ANS algebraic stacks of finite type over a field of characteristic 0 using trace methods and equivariant resolution of singularities. Time permitting, we discuss an ongoing work attempting to extend this result in characteristic p.
[ Reference URL ]Algebraic K-theory satisfies descent with respect to Nisnevich covers, which allows one to deduce global computations for schemes to the affine case. For algebraic stacks this is insufficient, since algebraic stacks with nontrivial stabilizers do not admit Nisnevich covers by affine schemes. However, a theorem of Deshmukh shows that any algebraic stack with separated diagonal admits a Nisnevich surjection from an affine scheme. The Atiyah—Segal completion theorem measures precisely the failure of algebraic K-theory to satisfy descent with respect to Nisnevich surjections. We show that it holds for ANS algebraic stacks of finite type over a field of characteristic 0 using trace methods and equivariant resolution of singularities. Time permitting, we discuss an ongoing work attempting to extend this result in characteristic p.
https://vova-sosnilo.com/
Tokyo-Nagoya Algebra Seminar
13:00-14:30 Online
Yuta Takaya (University of Tokyo)
Characteristic-free approaches around Yu's construction (Japanese)
https://www.math.nagoya-u.ac.jp/~aaron.chan/TNAseminar.html
Yuta Takaya (University of Tokyo)
Characteristic-free approaches around Yu's construction (Japanese)
[ Abstract ]
Yu's construction is one of the most wide-ranging constructions of supercuspidal representations. Recently, Fintzen, Kaletha, and Spice introduced a quadratic twist of this construction to build stable L-packets, which also appears in the geometric realization via positive-depth Deligne-Lusztig induction. In this talk, I will present a direct approach to twisted Yu's construction and explain how to remove technical conditions on small primes in the theory of Yu's construction and positive-depth Deligne-Lusztig induction.
Zoom ID 882 6509 3568 Password 616173
[ Reference URL ]Yu's construction is one of the most wide-ranging constructions of supercuspidal representations. Recently, Fintzen, Kaletha, and Spice introduced a quadratic twist of this construction to build stable L-packets, which also appears in the geometric realization via positive-depth Deligne-Lusztig induction. In this talk, I will present a direct approach to twisted Yu's construction and explain how to remove technical conditions on small primes in the theory of Yu's construction and positive-depth Deligne-Lusztig induction.
Zoom ID 882 6509 3568 Password 616173
https://www.math.nagoya-u.ac.jp/~aaron.chan/TNAseminar.html
2026/07/07
Operator Algebra Seminars
16:45-18:15 Room #126 (Graduate School of Math. Sci. Bldg.)
Nanami Hashimoto (Keio University)
Equivalence of categories of KK-theory or E-theory for $C^*$-algebras over topological spaces by reflection functors
[ Reference URL ]
https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm
Nanami Hashimoto (Keio University)
Equivalence of categories of KK-theory or E-theory for $C^*$-algebras over topological spaces by reflection functors
[ Reference URL ]
https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm
Tuesday Seminar on Topology
16:00-17:00 Online
Pre-registration required. See our seminar webpage.
Tatsuhiko Yagasaki (Kyoto Institute of Technology)
Topological properties of groups of volume-preserving diffeomorphisms and groups of uniform homeomorphisms (JAPANESE)
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html
Pre-registration required. See our seminar webpage.
Tatsuhiko Yagasaki (Kyoto Institute of Technology)
Topological properties of groups of volume-preserving diffeomorphisms and groups of uniform homeomorphisms (JAPANESE)
[ Abstract ]
This talk is a continuation of survey on topological properties of groups of homeomorphisms/diffeomorphisms on noncompact manifolds. As a subject related to ends of noncompact manifolds, we discuss volume transfer towards ends, which leads to the existence of continuous sections under the compact-open topology for the actions of diffeomorphism groups on the spaces of volume forms on noncompact manifolds (a noncompact version of Moser's theorem) and for the end charge homomorphisms introduced by Alpern and Prasad. We also give a brief survey on the local and end deformation properties in groups of uniform homeomorphisms on noncompact metric manifolds with the sup-metric.
[ Reference URL ]This talk is a continuation of survey on topological properties of groups of homeomorphisms/diffeomorphisms on noncompact manifolds. As a subject related to ends of noncompact manifolds, we discuss volume transfer towards ends, which leads to the existence of continuous sections under the compact-open topology for the actions of diffeomorphism groups on the spaces of volume forms on noncompact manifolds (a noncompact version of Moser's theorem) and for the end charge homomorphisms introduced by Alpern and Prasad. We also give a brief survey on the local and end deformation properties in groups of uniform homeomorphisms on noncompact metric manifolds with the sup-metric.
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html
2026/07/06
Seminar on Geometric Complex Analysis
10:30-12:00 Room #126 (Graduate School of Math. Sci. Bldg.)
Xiaojun Wu (Tsukuba Univ.)
Generalised Ueda Obstruction Classes and Non-Semipositive Line Bundles (English)
https://forms.gle/8ERsVDLuKHwbVzm57
Xiaojun Wu (Tsukuba Univ.)
Generalised Ueda Obstruction Classes and Non-Semipositive Line Bundles (English)
[ Abstract ]
Serre’s classical example provides a fundamental instance of a nef but non-semipositive line bundle and motivated the analytic definition of nefness introduced by Demailly–Peternell–Schneider. Building on subsequent developments by Koike, the classical Ueda obstruction classes provide a natural criterion for non-semipositivity. In this talk, we introduce a natural generalisation of the Ueda obstruction classes that is always well defined and for which the Chern curvature naturally determines representatives. As an application, we obtain an elementary and systematic method for constructing nef but non-semipositive line bundles.
[ Reference URL ]Serre’s classical example provides a fundamental instance of a nef but non-semipositive line bundle and motivated the analytic definition of nefness introduced by Demailly–Peternell–Schneider. Building on subsequent developments by Koike, the classical Ueda obstruction classes provide a natural criterion for non-semipositivity. In this talk, we introduce a natural generalisation of the Ueda obstruction classes that is always well defined and for which the Chern curvature naturally determines representatives. As an application, we obtain an elementary and systematic method for constructing nef but non-semipositive line bundles.
https://forms.gle/8ERsVDLuKHwbVzm57
Tokyo Probability Seminar
16:00-17:30 Room #126 (Graduate School of Math. Sci. Bldg.)
We are having teatime from 15:20 in the common room on the second floor. Please join us.
Tadahisa Funaki (BIMSA)
Interface motion from non-gradient Glauber-Kawasaki dynamics
We are having teatime from 15:20 in the common room on the second floor. Please join us.
Tadahisa Funaki (BIMSA)
Interface motion from non-gradient Glauber-Kawasaki dynamics
[ Abstract ]
Motivated by the problem of dynamic phase transitions, we study the derivation of interface motion from non-gradient Glauber-Kawasaki dynamics. In the balanced case, the limiting interface evolves according to the anisotropic curvature flow, while in the unbalanced case it is governed by a geometric Hamilton-Jacobi equation. We establish this result as a quantitative hydrodynamic limit and, by applying the method of quantitative homogenization, obtain convergence rates. We also investigate fluctuations of the interface and derive a linear stochastic partial differential equation. This talk is partially based on several joint works with Chenlin Gu (Tsinghua U), Han Wang (Tsinghua U), Shuhan Zhou (Peking U), Hyunjoon Park (Meiji U), Claudio Landim (IMPA), Sunder Sethuraman (U Arizona).
Motivated by the problem of dynamic phase transitions, we study the derivation of interface motion from non-gradient Glauber-Kawasaki dynamics. In the balanced case, the limiting interface evolves according to the anisotropic curvature flow, while in the unbalanced case it is governed by a geometric Hamilton-Jacobi equation. We establish this result as a quantitative hydrodynamic limit and, by applying the method of quantitative homogenization, obtain convergence rates. We also investigate fluctuations of the interface and derive a linear stochastic partial differential equation. This talk is partially based on several joint works with Chenlin Gu (Tsinghua U), Han Wang (Tsinghua U), Shuhan Zhou (Peking U), Hyunjoon Park (Meiji U), Claudio Landim (IMPA), Sunder Sethuraman (U Arizona).
2026/07/03
Algebraic Geometry Seminar
13:15-14:45 Room #117 (Graduate School of Math. Sci. Bldg.)
Shou Yoshikawa (Institute of Science Tokyo)
Hodge–Tate splitting and Akizuki–Nakano vanishing
Shou Yoshikawa (Institute of Science Tokyo)
Hodge–Tate splitting and Akizuki–Nakano vanishing
2026/07/01
Number Theory Seminar
17:00-18:00 Room #117 (Graduate School of Math. Sci. Bldg.)
ISHIKURA Rintaro (University of Tokyo)
On boundedness of the number of cuspidal automorphic representations of Mp(4) ordinary at p
ISHIKURA Rintaro (University of Tokyo)
On boundedness of the number of cuspidal automorphic representations of Mp(4) ordinary at p
[ Abstract ]
The notion of ordinary modular forms, introduced and developed in Hida theory, has played a central role in the study of p-adic families of automorphic forms. It is therefore natural to ask how this notion extends to automorphic representations of covering groups. This talk is concerned with p-ordinary cuspidal automorphic representations of the metaplectic group Mp(4) with holomorphic discrete series at infinity. Using two Iwahori-level Hecke operators, we define an ordinary projector and investigate the conditions for a representation to be ordinary at p. Fixing the level K, we prove a bound (depending only on K) for the number of genuine cuspidal automorphic representations of Mp(4) ordinary at p and containing nonzero K-fixed vectors, as the holomorphic weight varies.
The notion of ordinary modular forms, introduced and developed in Hida theory, has played a central role in the study of p-adic families of automorphic forms. It is therefore natural to ask how this notion extends to automorphic representations of covering groups. This talk is concerned with p-ordinary cuspidal automorphic representations of the metaplectic group Mp(4) with holomorphic discrete series at infinity. Using two Iwahori-level Hecke operators, we define an ordinary projector and investigate the conditions for a representation to be ordinary at p. Fixing the level K, we prove a bound (depending only on K) for the number of genuine cuspidal automorphic representations of Mp(4) ordinary at p and containing nonzero K-fixed vectors, as the holomorphic weight varies.
2026/06/30
Tuesday Seminar on Topology
16:00-17:30 Room #hybrid/123 (Graduate School of Math. Sci. Bldg.)
Pre-registration required. See our seminar webpage.
Sang-hyun Kim (Korea Institute For Advanced Study)
Structure and rigidity of manifold diffeomorphism groups (ENGLISH)
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html
Pre-registration required. See our seminar webpage.
Sang-hyun Kim (Korea Institute For Advanced Study)
Structure and rigidity of manifold diffeomorphism groups (ENGLISH)
[ Abstract ]
Given a manifold M and a structure S, we denote by Homeo(M;S) the group of S-preserving homeomorphisms of M. We will be particularly concerned with the case tha S is the C^r structure in the sense of Hölder continuity. In such a case, the group is written as Diff^r(M). The goal of this lecture series is to survey recent results and open questions on the rigidity of the group structures involving these groups. When M is a compact one-manifold, namely an interval or a circle, each real number r≥1 admits a finitely generated subgroup G_r of Diff^r(M) such that G_r never embeds into Diff^s(M) for any s>r. This generalizes observations by earlier foliation theorists on the case r=0 or r=1. In the second talk, I will propose a rigidity phenomenon regarding higher dimensional manifolds. Namely, we consider the question exactly when two manifold diffeomorphism groups Diff^r(M) and Diff^s(N) have the same logical structure. Modern findings regarding this question gives a generalization of classical results of Whittaker (1963), and of Takens-Filipkiewicz (1982). This talk is based on joint work with Thomas Koberda (UVa) and Javier de la Nuez-Gonzalez (KIAS).
[ Reference URL ]Given a manifold M and a structure S, we denote by Homeo(M;S) the group of S-preserving homeomorphisms of M. We will be particularly concerned with the case tha S is the C^r structure in the sense of Hölder continuity. In such a case, the group is written as Diff^r(M). The goal of this lecture series is to survey recent results and open questions on the rigidity of the group structures involving these groups. When M is a compact one-manifold, namely an interval or a circle, each real number r≥1 admits a finitely generated subgroup G_r of Diff^r(M) such that G_r never embeds into Diff^s(M) for any s>r. This generalizes observations by earlier foliation theorists on the case r=0 or r=1. In the second talk, I will propose a rigidity phenomenon regarding higher dimensional manifolds. Namely, we consider the question exactly when two manifold diffeomorphism groups Diff^r(M) and Diff^s(N) have the same logical structure. Modern findings regarding this question gives a generalization of classical results of Whittaker (1963), and of Takens-Filipkiewicz (1982). This talk is based on joint work with Thomas Koberda (UVa) and Javier de la Nuez-Gonzalez (KIAS).
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html
2026/06/29
Seminar on Geometric Complex Analysis
10:30-12:00 Room #126 (Graduate School of Math. Sci. Bldg.)
Chin-Yu Hsiao (National Taiwan University)
Heat kernel asymptotics for the $\bar{\partial}$-Neumann Laplacian on manifolds with boundary (English)
https://forms.gle/8ERsVDLuKHwbVzm57
Chin-Yu Hsiao (National Taiwan University)
Heat kernel asymptotics for the $\bar{\partial}$-Neumann Laplacian on manifolds with boundary (English)
[ Abstract ]
We study the heat kernel asymptotics of the $\bar{\partial}$-Neumann Laplacian associated with high tensor powers of a holomorphic line bundle. Specifically, for a relatively compact complex submanifold with smooth boundary in a complex manifold, we consider the $\bar{\partial}$-Neumann Laplacian acting on holomorphic sections of a holomorphic bundle over the submanifold. As the tensor power of the line bundle approaches infinity, we obtain explicit asymptotic expansions of the heat kernel in the submanifold's interior, on its boundary, and near the boundary. This is achieved by explicitly solving the heat equation for the weighted $\bar{\partial}$-Neumann Laplacian in domains that are not necessarily strongly pseudoconvex and showing uniform convergence of the associated scaled Laplacian's heat kernel to this solution. As an application, we establish analogue holomorphic Morse inequalities of Demailly on complex manifolds with boundary.
[ Reference URL ]We study the heat kernel asymptotics of the $\bar{\partial}$-Neumann Laplacian associated with high tensor powers of a holomorphic line bundle. Specifically, for a relatively compact complex submanifold with smooth boundary in a complex manifold, we consider the $\bar{\partial}$-Neumann Laplacian acting on holomorphic sections of a holomorphic bundle over the submanifold. As the tensor power of the line bundle approaches infinity, we obtain explicit asymptotic expansions of the heat kernel in the submanifold's interior, on its boundary, and near the boundary. This is achieved by explicitly solving the heat equation for the weighted $\bar{\partial}$-Neumann Laplacian in domains that are not necessarily strongly pseudoconvex and showing uniform convergence of the associated scaled Laplacian's heat kernel to this solution. As an application, we establish analogue holomorphic Morse inequalities of Demailly on complex manifolds with boundary.
https://forms.gle/8ERsVDLuKHwbVzm57
Tokyo Probability Seminar
16:00-17:30 Room #126 (Graduate School of Math. Sci. Bldg.)
We are having teatime from 15:20 in the common room on the second floor. Please join us.
Ryoichiro Noda (Waseda University)
Fine geometry of collision measures
We are having teatime from 15:20 in the common room on the second floor. Please join us.
Ryoichiro Noda (Waseda University)
Fine geometry of collision measures
[ Abstract ]
Given several independent stochastic processes, their collision measure is a random measure that records when and where they collide. In this talk, I will discuss fine geometric properties of collision measures for independent Markov processes on metric measure spaces. Under standard heat kernel estimates, we identify the local dimensions of the temporal and spatial marginals of the collision measure. We also determine the Hausdorff dimensions of their supports, as well as those of the corresponding sets of collision times and collision sites. Finally, we study logarithmic limsup gauges describing typical and thick collision times and sites.
Given several independent stochastic processes, their collision measure is a random measure that records when and where they collide. In this talk, I will discuss fine geometric properties of collision measures for independent Markov processes on metric measure spaces. Under standard heat kernel estimates, we identify the local dimensions of the temporal and spatial marginals of the collision measure. We also determine the Hausdorff dimensions of their supports, as well as those of the corresponding sets of collision times and collision sites. Finally, we study logarithmic limsup gauges describing typical and thick collision times and sites.
2026/06/26
Colloquium
15:30-16:30 Room #NISSAY Lecture Hall (Graduate School of Math. Sci. Bldg.)
Bez Neal (Graduate School of Mathematical Sciences, The University of Tokyo)
The Kakeya conjecture and the Brascamp-Lieb inequality (日本語)
Bez Neal (Graduate School of Mathematical Sciences, The University of Tokyo)
The Kakeya conjecture and the Brascamp-Lieb inequality (日本語)
[ Abstract ]
Despite being ostensibly a problem in geometric measure theory,
the Kakeya conjecture has huge significance in modern Fourier analysis.
After discussing this connection,
I will explain the relevance of the Brascamp-Lieb inequality in this context
and introduce some recent progress in the theory of this inequality.
Despite being ostensibly a problem in geometric measure theory,
the Kakeya conjecture has huge significance in modern Fourier analysis.
After discussing this connection,
I will explain the relevance of the Brascamp-Lieb inequality in this context
and introduce some recent progress in the theory of this inequality.
Geometric Analysis Seminar
13:30-14;30 Room #002 (Graduate School of Math. Sci. Bldg.)
Federica Dragoni (Cardiff University)
Convexity: from the Euclidean space to Riemannian and sub-Riemannian manifolds (英語)
https://sites.google.com/g.ecc.u-tokyo.ac.jp/geometricanalysisseminar/
Federica Dragoni (Cardiff University)
Convexity: from the Euclidean space to Riemannian and sub-Riemannian manifolds (英語)
[ Abstract ]
In this talk I will give an overview on different notions of convexity introduced in the last decades to generalise the standard (Euclidean) convexity to different geometries such as Riemannian manifolds, Carnot groups and the geometry of vector fields. Later I will show some more recent developments and how this new geometrical approach can connect most of the previous notions.
[ Reference URL ]In this talk I will give an overview on different notions of convexity introduced in the last decades to generalise the standard (Euclidean) convexity to different geometries such as Riemannian manifolds, Carnot groups and the geometry of vector fields. Later I will show some more recent developments and how this new geometrical approach can connect most of the previous notions.
https://sites.google.com/g.ecc.u-tokyo.ac.jp/geometricanalysisseminar/
Seminar on Probability and Statistics
13:30-14:30 Room #122 (Graduate School of Math. Sci. Bldg.)
Prof. Hsin-Hsiung 'Bill’ Huang (School of Data, Mathematical, and Statistical Sciences, University of Central Florida)
Scalable Bayesian Conformal Inference for High-Dimensional Spatiotemporal Zero-Inflated Count Data (English)
https://u-tokyo-ac-jp.zoom.us/meeting/register/UmviZSskR766wD4QoUvP2g
Prof. Hsin-Hsiung 'Bill’ Huang (School of Data, Mathematical, and Statistical Sciences, University of Central Florida)
Scalable Bayesian Conformal Inference for High-Dimensional Spatiotemporal Zero-Inflated Count Data (English)
[ Abstract ]
I will present a Bayesian framework for spatiotemporal count data with excess zeros, overdispersion, and ultrahigh-dimensional covariates. The model combines zero-inflated negative binomial regression, TPBN shrinkage priors for sparse fixed effects, graph-Laplacian or SPDE-type spatial random effects, smooth global time effects, and unit-specific Ornstein--Uhlenbeck SDE random effects. Pólya--Gamma augmentation yields a conditionally Gaussian structure, supporting both blocked Gibbs sampling and scalable structured variational inference. I will also discuss split conformal calibration for discrete predictive sets and an auxiliary LAQ/QMLE perspective for the OU component. Simulation studies and a measles surveillance analysis illustrate calibrated prediction and recovery of latent spatiotemporal structure.
[ Reference URL ]I will present a Bayesian framework for spatiotemporal count data with excess zeros, overdispersion, and ultrahigh-dimensional covariates. The model combines zero-inflated negative binomial regression, TPBN shrinkage priors for sparse fixed effects, graph-Laplacian or SPDE-type spatial random effects, smooth global time effects, and unit-specific Ornstein--Uhlenbeck SDE random effects. Pólya--Gamma augmentation yields a conditionally Gaussian structure, supporting both blocked Gibbs sampling and scalable structured variational inference. I will also discuss split conformal calibration for discrete predictive sets and an auxiliary LAQ/QMLE perspective for the OU component. Simulation studies and a measles surveillance analysis illustrate calibrated prediction and recovery of latent spatiotemporal structure.
https://u-tokyo-ac-jp.zoom.us/meeting/register/UmviZSskR766wD4QoUvP2g
2026/06/25
Applied Analysis
16:00-17:30 Room # 002 (Graduate School of Math. Sci. Bldg.)
Xiao Dongyuan (Tohoku University)
Complete classification of traveling wave solutions to monotone dynamical systems (Japanese)
Xiao Dongyuan (Tohoku University)
Complete classification of traveling wave solutions to monotone dynamical systems (Japanese)
[ Abstract ]
To study the propagation phenomena of solutions to the reaction-diffusion equation the asymptotic behavior of traveling wave solutions plays a crucial role. When the nonlinear reaction term satisfies the monostable condition, it is known that there exists a minimal traveling wave speed, and that traveling wave solutions exist for any speed c larger than or equal to the minimal speed. It has been shown, through simple phase plane analysis, that these traveling waves can be classified into three cases based on their decay rates.
It Is expected that a similar classification should hold for more general order-preserving systems, such as nonlocal diffusion equations, Lotka–Volterra systems, and reaction–diffusion equations with time delay. However, a complete classification remains unavailable because direct phase plane analysis is no longer applicable in these settings. In this talk, I will introduce a method based on comparison argument and sliding method to classify traveling waves. This research is based on joint work with Maolin Zhou (Nankai University) and Chang-hong Wu (National Yang Ming Chiao Tung University).
To study the propagation phenomena of solutions to the reaction-diffusion equation the asymptotic behavior of traveling wave solutions plays a crucial role. When the nonlinear reaction term satisfies the monostable condition, it is known that there exists a minimal traveling wave speed, and that traveling wave solutions exist for any speed c larger than or equal to the minimal speed. It has been shown, through simple phase plane analysis, that these traveling waves can be classified into three cases based on their decay rates.
It Is expected that a similar classification should hold for more general order-preserving systems, such as nonlocal diffusion equations, Lotka–Volterra systems, and reaction–diffusion equations with time delay. However, a complete classification remains unavailable because direct phase plane analysis is no longer applicable in these settings. In this talk, I will introduce a method based on comparison argument and sliding method to classify traveling waves. This research is based on joint work with Maolin Zhou (Nankai University) and Chang-hong Wu (National Yang Ming Chiao Tung University).
2026/06/23
Operator Algebra Seminars
16:45-18:15 Room #126 (Graduate School of Math. Sci. Bldg.)
Ravi Mistry (the University of Tokyo)
Knots, Invariants, QFT, and Beyond
[ Reference URL ]
https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm
Ravi Mistry (the University of Tokyo)
Knots, Invariants, QFT, and Beyond
[ Reference URL ]
https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm
Tuesday Seminar on Topology
16:00-17:30 Room #hybrid/056 (Graduate School of Math. Sci. Bldg.)
Pre-registration required. See our seminar webpage.
Andrei Pajitnov (Université de Nantes)
Morse-Novikov theory for links (ENGLISH)
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html
Pre-registration required. See our seminar webpage.
Andrei Pajitnov (Université de Nantes)
Morse-Novikov theory for links (ENGLISH)
[ Abstract ]
Let M be a compact manifold with a non-empty boundary N, and x an element of the first cohomology group of M. We assume that the restriction of x to N can be represented by a fibration over a circle. The Morse-Novikov number MN(M,x) is the minimal possible number of critical points of a Morse map f of M to a circle, such that [f]=x, and the restriction of f to N is a fibration over the circle. In this talk we present our results about the Morse-Novikov numbers for the exteriors of links in 3-sphere. This is joint work with L. Chen and H. Endo.
[ Reference URL ]Let M be a compact manifold with a non-empty boundary N, and x an element of the first cohomology group of M. We assume that the restriction of x to N can be represented by a fibration over a circle. The Morse-Novikov number MN(M,x) is the minimal possible number of critical points of a Morse map f of M to a circle, such that [f]=x, and the restriction of f to N is a fibration over the circle. In this talk we present our results about the Morse-Novikov numbers for the exteriors of links in 3-sphere. This is joint work with L. Chen and H. Endo.
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html
2026/06/22
Seminar on Geometric Complex Analysis
10:30-12:00 Room #126 (Graduate School of Math. Sci. Bldg.)
Online only. No in-person attendance.
Naoto Yotsutani (Shizuoka Univ./IMAG, Univ. Montpellier)
Secondary polytopes of spherical varieties (Japanese)
https://forms.gle/8ERsVDLuKHwbVzm57
Online only. No in-person attendance.
Naoto Yotsutani (Shizuoka Univ./IMAG, Univ. Montpellier)
Secondary polytopes of spherical varieties (Japanese)
[ Abstract ]
This talk is based on ongoing joint work with Thibaut Delcroix and King Leung Lee. Our main objective is to investigate the Chow stability of spherical varieties.
A celebrated theorem of Gelfand, Kapranov, Sturmfels, and Zelevinsky (1992) states that the Chow polytopes of projective toric varieties coincide with their secondary polytopes. In the spherical setting, one can construct an analogous polytope, which may be viewed as a natural generalization of the secondary polytope of a toric variety. In this talk, I will explain the construction of this polytope and its relation to Chow stability. Particular emphasis will be placed on how the classical GKZ argument in the toric setting can be adapted to the broader context of spherical varieties.
[ Reference URL ]This talk is based on ongoing joint work with Thibaut Delcroix and King Leung Lee. Our main objective is to investigate the Chow stability of spherical varieties.
A celebrated theorem of Gelfand, Kapranov, Sturmfels, and Zelevinsky (1992) states that the Chow polytopes of projective toric varieties coincide with their secondary polytopes. In the spherical setting, one can construct an analogous polytope, which may be viewed as a natural generalization of the secondary polytope of a toric variety. In this talk, I will explain the construction of this polytope and its relation to Chow stability. Particular emphasis will be placed on how the classical GKZ argument in the toric setting can be adapted to the broader context of spherical varieties.
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.
Manasa Nagatsu (Kyoto University)
Large $N$ expansion for smooth multi-trace spectral statistics of
classical matrix ensembles, central limit theorems and matrix integrals.
We are having teatime from 15:15 in the common room on the second floor. Please join us.
Manasa Nagatsu (Kyoto University)
Large $N$ expansion for smooth multi-trace spectral statistics of
classical matrix ensembles, central limit theorems and matrix integrals.
[ Abstract ]
We consider expectations of the form $E [tr h_1(X_1^N)... tr h_r(X_r^N)]$,
where $X_i^N$ are self-adjoint polynomials in various independent
classical random matrices and $h_i$ are smooth test function and obtain a
large $N$ expansion of these quantities, building on the framework of
polynomial approximation and Bernstein-type inequalities recently
developed by Chen, Garza-Vargas, Tropp, and van Handel.
As applications of the above, we prove the higher-order asymptotic
vanishing of cumulants for smooth linear statistics, establish a Central
Limit Theorem, and demonstrate the existence of formal asymptotic
expansions for the free energy and observables of matrix integrals with
smooth potentials.
In addition to presenting these results, we will briefly review the role
of linear statistics in random matrix theory and discuss the motivation
behind the large $N$ expansion framework introduced in the context of
strong convergence.
This talk is based on joint work with Benoit Collins.
We consider expectations of the form $E [tr h_1(X_1^N)... tr h_r(X_r^N)]$,
where $X_i^N$ are self-adjoint polynomials in various independent
classical random matrices and $h_i$ are smooth test function and obtain a
large $N$ expansion of these quantities, building on the framework of
polynomial approximation and Bernstein-type inequalities recently
developed by Chen, Garza-Vargas, Tropp, and van Handel.
As applications of the above, we prove the higher-order asymptotic
vanishing of cumulants for smooth linear statistics, establish a Central
Limit Theorem, and demonstrate the existence of formal asymptotic
expansions for the free energy and observables of matrix integrals with
smooth potentials.
In addition to presenting these results, we will briefly review the role
of linear statistics in random matrix theory and discuss the motivation
behind the large $N$ expansion framework introduced in the context of
strong convergence.
This talk is based on joint work with Benoit Collins.
2026/06/18
Logic
15:30-17:30 Room #122 (Graduate School of Math. Sci. Bldg.)
Paul Larson (Miami University)
Discontinuous homomorphisms without Hamel bases
Paul Larson (Miami University)
Discontinuous homomorphisms without Hamel bases
[ Abstract ]
A Hamel basis for the real line is a basis for the line over the scalar field of rational numbers. The Axiom of Choice implies that Hamel bases exist. It is a classical fact that every measurable homomorphism from the additive group on the real line to itself is continuous, and therefore is given by multiplication by some real number. However, permutations of Hamel bases naturally give rise to discontinuous homomorphisms. In this talk we will show that this implication cannot be reversed, by forcing to produce a model of ZF in which there exists a discontinuous homomorphism but there is no Hamel basis. This is joint work with Saharon Shelah.
A Hamel basis for the real line is a basis for the line over the scalar field of rational numbers. The Axiom of Choice implies that Hamel bases exist. It is a classical fact that every measurable homomorphism from the additive group on the real line to itself is continuous, and therefore is given by multiplication by some real number. However, permutations of Hamel bases naturally give rise to discontinuous homomorphisms. In this talk we will show that this implication cannot be reversed, by forcing to produce a model of ZF in which there exists a discontinuous homomorphism but there is no Hamel basis. This is joint work with Saharon Shelah.
2026/06/16
Operator Algebra Seminars
16:45-18:15 Room #126 (Graduate School of Math. Sci. Bldg.)
Hiroki Ishikura (RIMS, Kyoto Univ.)
Borel planar complexes and soficity
[ Reference URL ]
https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm
Hiroki Ishikura (RIMS, Kyoto Univ.)
Borel planar complexes and soficity
[ Reference URL ]
https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm
Tuesday Seminar on Topology
16:00-17:30 Room #hybrid/128 (Graduate School of Math. Sci. Bldg.)
Pre-registration required. See our seminar webpage.
Yuto Moriwaki (RIKEN iTHEMS)
Conformally flat factorization homology (JAPANESE)
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html
Pre-registration required. See our seminar webpage.
Yuto Moriwaki (RIKEN iTHEMS)
Conformally flat factorization homology (JAPANESE)
[ Abstract ]
This talk presents conformally flat factorization homology, introduced as a conformal Riemannian analogue of Lurie's factorization homology. Ordinary factorization homology takes a d-disk algebra as input and produces invariants of d-dimensional manifolds that are independent of the choice of metric. In contrast, conformally flat factorization homology takes as input a conformally flat d-disk algebra, which is an algebra over the operad formed by conformal open embeddings of disks, and constructs, via its left Kan extension, metric-dependent invariants of conformally flat Riemannian manifolds.
This theory provides a framework connecting representations of local conformal transformations with Riemannian geometric invariants, and describes the local structure of d-dimensional conformal field theory. The talk will also discuss concrete examples constructed using Bergman spaces and Grunsky operators in dimension two, and using unitary representations of SO+(d,1) in dimensions three and higher.
This talk is based on arXiv:2602.08729 and arXiv:2603.06491.
[ Reference URL ]This talk presents conformally flat factorization homology, introduced as a conformal Riemannian analogue of Lurie's factorization homology. Ordinary factorization homology takes a d-disk algebra as input and produces invariants of d-dimensional manifolds that are independent of the choice of metric. In contrast, conformally flat factorization homology takes as input a conformally flat d-disk algebra, which is an algebra over the operad formed by conformal open embeddings of disks, and constructs, via its left Kan extension, metric-dependent invariants of conformally flat Riemannian manifolds.
This theory provides a framework connecting representations of local conformal transformations with Riemannian geometric invariants, and describes the local structure of d-dimensional conformal field theory. The talk will also discuss concrete examples constructed using Bergman spaces and Grunsky operators in dimension two, and using unitary representations of SO+(d,1) in dimensions three and higher.
This talk is based on arXiv:2602.08729 and arXiv:2603.06491.
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html
2026/06/15
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.
Tomoyuki Ichiba (University of California Santa Barbara)
Feynman formula for discrete-time quantum walk and its applications
We are having teatime from 15:15 in the common room on the second floor. Please join us.
Tomoyuki Ichiba (University of California Santa Barbara)
Feynman formula for discrete-time quantum walk and its applications
[ Abstract ]
We explicitly connect (discrete-time) quantum walks on Z with a four-state Markov additive process via a Feynman-type formula. Using this representation, we derive a relation between the spectral decomposition of the Markov additive process and the limiting density of the homogeneous quantum walk. In addition, we consider a space-time rescaling of quantum walks, which leads to a system of quantum transport PDEs of Dirac type in continuous time and space with phase interaction and potential terms. Our probabilistic representation for this type of PDE offers its stochastic extension as well as an efficient Monte Carlo computational technique. This is joint work with Jean-Pierre Fouque and Ka Lok Lam.
We explicitly connect (discrete-time) quantum walks on Z with a four-state Markov additive process via a Feynman-type formula. Using this representation, we derive a relation between the spectral decomposition of the Markov additive process and the limiting density of the homogeneous quantum walk. In addition, we consider a space-time rescaling of quantum walks, which leads to a system of quantum transport PDEs of Dirac type in continuous time and space with phase interaction and potential terms. Our probabilistic representation for this type of PDE offers its stochastic extension as well as an efficient Monte Carlo computational technique. This is joint work with Jean-Pierre Fouque and Ka Lok Lam.
FJ-LMI Seminar
10:30-12:00 Room #002 (Graduate School of Math. Sci. Bldg.)
Eric Leclerc, . Fabrizio Cleri, Yuki Miura, Stephane Poulain (LIMMS & IIS of The University of Tokyo)
- Introduction to a quantum inspired model of the mitochondria dysfunction in liver disease;
- From Boltzmann to Lindblad: quantum systems out of equilibrium;
- A hybrid liver model of mechanistic ODE systems and machine learning;
- Presentation of research background in bioinformatics and genomics, and introduction to new research projects for in silico liver organ physiology modeling using AI and informatics tools. (英語)
Eric Leclerc, . Fabrizio Cleri, Yuki Miura, Stephane Poulain (LIMMS & IIS of The University of Tokyo)
- Introduction to a quantum inspired model of the mitochondria dysfunction in liver disease;
- From Boltzmann to Lindblad: quantum systems out of equilibrium;
- A hybrid liver model of mechanistic ODE systems and machine learning;
- Presentation of research background in bioinformatics and genomics, and introduction to new research projects for in silico liver organ physiology modeling using AI and informatics tools. (英語)
[ Abstract ]
These 4 short presentations will focus on possible interactions between two laboratories.
These 4 short presentations will focus on possible interactions between two laboratories.
2026/06/10
Number Theory Seminar
17:00-18:00 Room #117 (Graduate School of Math. Sci. Bldg.)
Ana Caraiani (Imperial College London)
Towards an Eichler-Shimura decomposition for ordinary p-adic Siegel modular forms
Ana Caraiani (Imperial College London)
Towards an Eichler-Shimura decomposition for ordinary p-adic Siegel modular forms
[ Abstract ]
There are two different ways to construct families of ordinary p-adic Siegel modular forms. One is by p-adically interpolating classes in Betti cohomology, first introduced by Hida and then given a more representation-theoretic interpretation by Emerton. The other is by p-adically interpolating classes in coherent cohomology, once again pioneered by Hida and generalised in recent years by Boxer and Pilloni. I will explain these two constructions and then discuss joint work in progress with James Newton and Juan Esteban Rodríguez Camargo that aims to compare them.
There are two different ways to construct families of ordinary p-adic Siegel modular forms. One is by p-adically interpolating classes in Betti cohomology, first introduced by Hida and then given a more representation-theoretic interpretation by Emerton. The other is by p-adically interpolating classes in coherent cohomology, once again pioneered by Hida and generalised in recent years by Boxer and Pilloni. I will explain these two constructions and then discuss joint work in progress with James Newton and Juan Esteban Rodríguez Camargo that aims to compare them.
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