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Seminar information archive
Seminar information archive ～12/24｜Today's seminar 12/25 | Future seminars 12/26～
2025/12/23
Tuesday Seminar on Topology
17:30-18:30 Room #hybrid/056 (Graduate School of Math. Sci. Bldg.)
Pre-registration required. See our seminar webpage.
Mayuko Yamashita (Perimeter Institute for Theoretical Physics / RIKEN)
Geometric engineering in Topological Modular Forms (JAPANESE)
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html
Pre-registration required. See our seminar webpage.
Mayuko Yamashita (Perimeter Institute for Theoretical Physics / RIKEN)
Geometric engineering in Topological Modular Forms (JAPANESE)
[ Abstract ]
I will explain my ongoing project to construct a functor from the category of conformal field theories to the TMF-module category, and realizing the symmetry of CFTs in genuine equivariance in TMF. I will explain the progress on the cases related to the K3 sigma model, with the motivation coming from the Mathieu moonshine.
[ Reference URL ]I will explain my ongoing project to construct a functor from the category of conformal field theories to the TMF-module category, and realizing the symmetry of CFTs in genuine equivariance in TMF. I will explain the progress on the cases related to the K3 sigma model, with the motivation coming from the Mathieu moonshine.
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html
2025/12/22
Seminar on Geometric Complex Analysis
10:30-12:00 Room #128 (Graduate School of Math. Sci. Bldg.)
Keiji Oguiso (Univ. of Tokyo)
Algebraic dynamics of Calabi-Yau manifolds of Wehler type (Japanese)
https://forms.gle/gTP8qNZwPyQyxjTj8
Keiji Oguiso (Univ. of Tokyo)
Algebraic dynamics of Calabi-Yau manifolds of Wehler type (Japanese)
[ Abstract ]
A general hypersurface $X$ of multi-degree 2 in $(\Bbb P^1)^{d+1}$ is called a Calabi-Yau manifold of Wehler type (of dimension $d$). In this talk, after recalling some remarkable properties of $X$ found by Cantat and me, I would like to show that $X$ has a birational primitive automorphism, in particular a birational automorphism with Zariski dense orbit, in any $d \ge 2$.
[ Reference URL ]A general hypersurface $X$ of multi-degree 2 in $(\Bbb P^1)^{d+1}$ is called a Calabi-Yau manifold of Wehler type (of dimension $d$). In this talk, after recalling some remarkable properties of $X$ found by Cantat and me, I would like to show that $X$ has a birational primitive automorphism, in particular a birational automorphism with Zariski dense orbit, in any $d \ge 2$.
https://forms.gle/gTP8qNZwPyQyxjTj8
Tokyo-Nagoya Algebra Seminar
16:30-18:00 Online
Riku Fushimi (Nagoya University)
siltingとsimple-minded collectionの双対性 (Japanese)
[ Reference URL ]
https://www.math.nagoya-u.ac.jp/~aaron.chan/TNAseminar.html
Riku Fushimi (Nagoya University)
siltingとsimple-minded collectionの双対性 (Japanese)
[ Reference URL ]
https://www.math.nagoya-u.ac.jp/~aaron.chan/TNAseminar.html
2025/12/20
Seminar on Probability and Statistics
10:30-17:10 Room # (Graduate School of Math. Sci. Bldg.)
- (-)
- (-)
[ Reference URL ]
https://sites.google.com/view/yuimatutorial2025/
- (-)
- (-)
[ Reference URL ]
https://sites.google.com/view/yuimatutorial2025/
2025/12/19
Algebraic Geometry Seminar
13:30-15:00 Room #118 (Graduate School of Math. Sci. Bldg.)
Hokuto Konno (University of Tokyo)
On diffeomorphisms of complex surfaces
Hokuto Konno (University of Tokyo)
On diffeomorphisms of complex surfaces
[ Abstract ]
Many basic questions about the diffeomorphism groups of complex surfaces remain unresolved. For example, until recently it was unknown whether there exists a simply-connected complex surface admitting a diffeomorphism that acts trivially on the intersection form but is not isotopic to the identity. We have recently answered this question by showing that certain elliptic surfaces do admit such diffeomorphisms. These diffeomorphisms are obtained as suitable compositions of reflections along (-2)-curves. Moreover, this result also provides a negative answer to a question of Donaldson in symplectic geometry. This talk is based on joint work with David Baraglia, and with Jianfeng Lin, Anubhav Mukherjee, and Juan Muñoz-Echániz.
Many basic questions about the diffeomorphism groups of complex surfaces remain unresolved. For example, until recently it was unknown whether there exists a simply-connected complex surface admitting a diffeomorphism that acts trivially on the intersection form but is not isotopic to the identity. We have recently answered this question by showing that certain elliptic surfaces do admit such diffeomorphisms. These diffeomorphisms are obtained as suitable compositions of reflections along (-2)-curves. Moreover, this result also provides a negative answer to a question of Donaldson in symplectic geometry. This talk is based on joint work with David Baraglia, and with Jianfeng Lin, Anubhav Mukherjee, and Juan Muñoz-Echániz.
Algebraic Geometry Seminar
15:15-16:45 Room #118 (Graduate School of Math. Sci. Bldg.)
JongHae Keum (Korea Institute for Advanced Study)
Fake quadric surfaces
JongHae Keum (Korea Institute for Advanced Study)
Fake quadric surfaces
[ Abstract ]
A smooth projective complex surface S is called a Q-homology quadric if it has the same Betti numbers as the smooth quadric surface.
Let S be a Q-homology quadric. Then its cohomology lattice is of rank 2, (even or odd) unimodular.
By the classification theory of surfaces, S is either rational or of general type.
In the latter case, S is called a fake Q-homology quadric.
There is an unsolved question raised by Hirzebruch: does there exist a surface of general type which is homeomorphic to the smooth quadric surface?
I will report recent progress on these surfaces.
A smooth projective complex surface S is called a Q-homology quadric if it has the same Betti numbers as the smooth quadric surface.
Let S be a Q-homology quadric. Then its cohomology lattice is of rank 2, (even or odd) unimodular.
By the classification theory of surfaces, S is either rational or of general type.
In the latter case, S is called a fake Q-homology quadric.
There is an unsolved question raised by Hirzebruch: does there exist a surface of general type which is homeomorphic to the smooth quadric surface?
I will report recent progress on these surfaces.
2025/12/18
Discrete mathematical modelling seminar
17:00-18:30 Room #118 (Graduate School of Math. Sci. Bldg.)
Ian Marquette (La Trobe University)
The classification of superintegrable systems with higher-order symmetries and related algebraic structures (English)
Ian Marquette (La Trobe University)
The classification of superintegrable systems with higher-order symmetries and related algebraic structures (English)
[ Abstract ]
Superintegrable systems admit more symmetries than degrees of freedom. The case of maximally superintegrable systems is characterized by 2n-1 integrals for n degrees of freedom. They possess rich mathematical structures and are related to orthogonal polynomials, special functions, and representation theory. The problem of classifying superintegrable systems was solved for quadratically superintegrable Hamiltonians in 2D conformally flat spaces about 20 years ago. The classification of superintegrable systems in higher-dimensional Riemannian spaces or with higher-order integrals is much more involved, and some partial results are known in three dimensions. These systems have attracted interest because they lead to algebraic structures known as polynomial algebras, which also appear in other contexts of mathematical physics.
This talk is devoted to discussing different approaches and recent results related to the classification of superintegrable systems with second-order and higher-order symmetries and the associated algebraic structures. In the direct approach, consisting of solving systems of partial differential equations, compatibility equations can be related to the works of Bureau, Chazy, and Cosgrove on higher-order nonlinear differential equations and Painlevé transcendents. I will present some examples related to the fourth and sixth Painlevé transcendents and demonstrate that their integrals lead to polynomial algebras. We discuss how these algebraic structures can still be used to gain insight into the spectrum.
I will discuss another and more recent approach to classifying superintegrable systems, which build a completely algebraic setting and on higher-degree polynomials in the enveloping algebra of Lie algebras. This allows the construction of algebraic Hamiltonians, integrals, and new perspectives on their associated algebraic structures. This approach offers greater flexibility, as different realizations can be used. This notion of the commutant leads to generalizations of Racah-type algebras.
Superintegrable systems admit more symmetries than degrees of freedom. The case of maximally superintegrable systems is characterized by 2n-1 integrals for n degrees of freedom. They possess rich mathematical structures and are related to orthogonal polynomials, special functions, and representation theory. The problem of classifying superintegrable systems was solved for quadratically superintegrable Hamiltonians in 2D conformally flat spaces about 20 years ago. The classification of superintegrable systems in higher-dimensional Riemannian spaces or with higher-order integrals is much more involved, and some partial results are known in three dimensions. These systems have attracted interest because they lead to algebraic structures known as polynomial algebras, which also appear in other contexts of mathematical physics.
This talk is devoted to discussing different approaches and recent results related to the classification of superintegrable systems with second-order and higher-order symmetries and the associated algebraic structures. In the direct approach, consisting of solving systems of partial differential equations, compatibility equations can be related to the works of Bureau, Chazy, and Cosgrove on higher-order nonlinear differential equations and Painlevé transcendents. I will present some examples related to the fourth and sixth Painlevé transcendents and demonstrate that their integrals lead to polynomial algebras. We discuss how these algebraic structures can still be used to gain insight into the spectrum.
I will discuss another and more recent approach to classifying superintegrable systems, which build a completely algebraic setting and on higher-degree polynomials in the enveloping algebra of Lie algebras. This allows the construction of algebraic Hamiltonians, integrals, and new perspectives on their associated algebraic structures. This approach offers greater flexibility, as different realizations can be used. This notion of the commutant leads to generalizations of Racah-type algebras.
2025/12/16
Numerical Analysis Seminar
16:30-18:00 Room #002 (Graduate School of Math. Sci. Bldg.)
Laurent Mertz (City University of Hong Kong)
A Control Variate Method Driven by Diffusion Approximation (English)
https://sites.google.com/g.ecc.u-tokyo.ac.jp/utnas-bulletin-board/
Laurent Mertz (City University of Hong Kong)
A Control Variate Method Driven by Diffusion Approximation (English)
[ Abstract ]
We present a control variate estimator for a quantity that can be expressed as the expectation of a functional of a random process, that is itself the solution of a differential equation driven by fast mean-reverting ergodic forces. The control variate is the expectation of the same functional for the limit diffusion process that approximates the original process when the mean-reversion time goes to zero. To get an efficient control variate estimator, we propose a coupling method to build the original process and the limit diffusion process. We show that the correlation between the two processes indeed goes to one when the mean reversion time goes to zero and we quantify the convergence rate, which makes it possible to characterize the variance reduction of the proposed control variate method. The efficiency of the method is illustrated on a few examples. This is joint work with Josselin Garnier (École Polytechnique, France). Link to the paper: https://doi.org/10.1002/cpa.21976
[ Reference URL ]We present a control variate estimator for a quantity that can be expressed as the expectation of a functional of a random process, that is itself the solution of a differential equation driven by fast mean-reverting ergodic forces. The control variate is the expectation of the same functional for the limit diffusion process that approximates the original process when the mean-reversion time goes to zero. To get an efficient control variate estimator, we propose a coupling method to build the original process and the limit diffusion process. We show that the correlation between the two processes indeed goes to one when the mean reversion time goes to zero and we quantify the convergence rate, which makes it possible to characterize the variance reduction of the proposed control variate method. The efficiency of the method is illustrated on a few examples. This is joint work with Josselin Garnier (École Polytechnique, France). Link to the paper: https://doi.org/10.1002/cpa.21976
https://sites.google.com/g.ecc.u-tokyo.ac.jp/utnas-bulletin-board/
Tuesday Seminar on Topology
17:00-18:00 Online
Pre-registration required. See our seminar webpage.
Tomoshige Yukita (Ashikaga University)
Continuity and minimality of growth rates of Coxeter systems (JAPANESE)
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html
Pre-registration required. See our seminar webpage.
Tomoshige Yukita (Ashikaga University)
Continuity and minimality of growth rates of Coxeter systems (JAPANESE)
[ Abstract ]
A pair (G, S) consisting of a group G and an ordered finite generating set S is called a marked group. On the set of all marked groups, one can define a distance that measures how similar the neighborhoods of the identity element in their Cayley graphs are. This space is called the space of marked groups. For a marked group, the function that counts the number of elements whose word length with respect to S is k is called the growth function, and the quantity describing its rate of divergence is called the growth rate. In this talk, we will discuss the continuity of the growth rate for marked Coxeter systems, and the problem of determining the minimal growth rate among Coxeter systems that are lattices in the isometry group of hyperbolic space.
[ Reference URL ]A pair (G, S) consisting of a group G and an ordered finite generating set S is called a marked group. On the set of all marked groups, one can define a distance that measures how similar the neighborhoods of the identity element in their Cayley graphs are. This space is called the space of marked groups. For a marked group, the function that counts the number of elements whose word length with respect to S is k is called the growth function, and the quantity describing its rate of divergence is called the growth rate. In this talk, we will discuss the continuity of the growth rate for marked Coxeter systems, and the problem of determining the minimal growth rate among Coxeter systems that are lattices in the isometry group of hyperbolic space.
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html
2025/12/11
Tokyo-Nagoya Algebra Seminar
13:00-14:30 Room #056 (Graduate School of Math. Sci. Bldg.)
Hybrid meeting, Zoom ID 895 8731 1175 Password 489352
Paul Balmer (UCLA)
The stable permutation category of a finite group (English)
https://www.math.nagoya-u.ac.jp/~aaron.chan/TNAseminar.html
Hybrid meeting, Zoom ID 895 8731 1175 Password 489352
Paul Balmer (UCLA)
The stable permutation category of a finite group (English)
[ Abstract ]
In this joint work with Martin Gallauer, we discuss the definition of the stable permutation category in modular representation theory. That category should be to the ordinary stable module category what the derived permutation category is to the ordinary derived category. Our construction is inspired by the picture provided by tensor-triangular geometry. We also use this geometric picture to decide when this new stable permutation category is connected or not, and to compute some components.
[ Reference URL ]In this joint work with Martin Gallauer, we discuss the definition of the stable permutation category in modular representation theory. That category should be to the ordinary stable module category what the derived permutation category is to the ordinary derived category. Our construction is inspired by the picture provided by tensor-triangular geometry. We also use this geometric picture to decide when this new stable permutation category is connected or not, and to compute some components.
https://www.math.nagoya-u.ac.jp/~aaron.chan/TNAseminar.html
2025/12/10
Number Theory Seminar
17:00-18:00 Room #117 (Graduate School of Math. Sci. Bldg.)
Paul Balmer (University of California, Los Angeles)
The spectrum of Artin motives
Paul Balmer (University of California, Los Angeles)
The spectrum of Artin motives
[ Abstract ]
In this joint work with Martin Gallauer, we investigate the tensor-triangular geometry of the category of Artin motives with coefficients of positive characteristic. This problem relates to modular representation theory of profinite groups and to the category of permutation modules. We shall explain some of the techniques that come into play in the study of the latter.
In this joint work with Martin Gallauer, we investigate the tensor-triangular geometry of the category of Artin motives with coefficients of positive characteristic. This problem relates to modular representation theory of profinite groups and to the category of permutation modules. We shall explain some of the techniques that come into play in the study of the latter.
2025/12/09
Tuesday Seminar of Analysis
16:00-17:30 Room # 002 (Graduate School of Math. Sci. Bldg.)
Marco Squassina (Università Cattolica del Sacro Cuore)
Log-concave solutions of the log-Schrodinger equation in a convex domain (English)
Marco Squassina (Università Cattolica del Sacro Cuore)
Log-concave solutions of the log-Schrodinger equation in a convex domain (English)
[ Abstract ]
First, we discuss some recent results on power concavity for certain classes of quasi-linear elliptic problems. We then turn our attention to a new problem involving the so-called log-Schrödinger equation, which cannot be addressed within the standard framework. To handle this, we introduce new techniques that lead to the existence of log-concave solutions to the log-Schrödinger equation in convex domains. Finally, we conclude with a brief discussion of (quantitative) partial concavity results for both elliptic and parabolic problems, as well as some perspectives on future developments concerning (quantitative) quasi-radiality results for problems in the ball.
First, we discuss some recent results on power concavity for certain classes of quasi-linear elliptic problems. We then turn our attention to a new problem involving the so-called log-Schrödinger equation, which cannot be addressed within the standard framework. To handle this, we introduce new techniques that lead to the existence of log-concave solutions to the log-Schrödinger equation in convex domains. Finally, we conclude with a brief discussion of (quantitative) partial concavity results for both elliptic and parabolic problems, as well as some perspectives on future developments concerning (quantitative) quasi-radiality results for problems in the ball.
Operator Algebra Seminars
16:45-18:15 Room #126 (Graduate School of Math. Sci. Bldg.)
Dan Voiculescu (UC Berkeley)
Around entropy in free probability theory
[ Reference URL ]
https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm
Dan Voiculescu (UC Berkeley)
Around entropy in free probability theory
[ Reference URL ]
https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm
Tuesday Seminar on Topology
17:00-18:30 Room #hybrid/056 (Graduate School of Math. Sci. Bldg.)
Pre-registration required. See our seminar webpage.
Yusuke Kuno (Tsuda University)
Emergent version of Drinfeld's associator equations (JAPANESE)
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html
Pre-registration required. See our seminar webpage.
Yusuke Kuno (Tsuda University)
Emergent version of Drinfeld's associator equations (JAPANESE)
[ Abstract ]
In 2012, Alekseev and Torossian proved that any solution of Drinfeld's associator equations gives rise to a solution of the Kashiwara-Vergne equations. Both equations arise in natural topological contexts. For the former, these are knots and braids in 3-space, and for the latter there are at least two contexts: one is the w-foams, a certain Reidemeister theory of singular surfaces in 4-space, and the other is the Goldman-Turaev loop operations on oriented 2-manifolds. With the hope of getting a better understanding of the relations among these topological objects, we introduce the concept of emergent braids, a low-degree Vassiliev quotient of braids over a punctured disk. Then we discuss a work in progress on the associated formality equations, the emergent version of Drinfeld's associator equations. This talk is partially based on a joint work with D. Bar-Natan, Z, Dancso, T. Hogan and D. Lin.
[ Reference URL ]In 2012, Alekseev and Torossian proved that any solution of Drinfeld's associator equations gives rise to a solution of the Kashiwara-Vergne equations. Both equations arise in natural topological contexts. For the former, these are knots and braids in 3-space, and for the latter there are at least two contexts: one is the w-foams, a certain Reidemeister theory of singular surfaces in 4-space, and the other is the Goldman-Turaev loop operations on oriented 2-manifolds. With the hope of getting a better understanding of the relations among these topological objects, we introduce the concept of emergent braids, a low-degree Vassiliev quotient of braids over a punctured disk. Then we discuss a work in progress on the associated formality equations, the emergent version of Drinfeld's associator equations. This talk is partially based on a joint work with D. Bar-Natan, Z, Dancso, T. Hogan and D. Lin.
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html
Numerical Analysis Seminar
16:30-18:00 Room #122 (Graduate School of Math. Sci. Bldg.)
Dorin Bucur (Université Savoie Mont Blanc)
On polygonal nonlocal isoperimetric inequalities: Hardy-Littlewood, Riesz, Faber-Krahn (English)
https://sites.google.com/g.ecc.u-tokyo.ac.jp/utnas-bulletin-board/
Dorin Bucur (Université Savoie Mont Blanc)
On polygonal nonlocal isoperimetric inequalities: Hardy-Littlewood, Riesz, Faber-Krahn (English)
[ Abstract ]
The starting point is the Faber-Krahn inequality on the first eigenvalue of the Dirichlet Laplacian. Many refinements were obtained in the last years, mainly due to the use of recent techniques based on the analysis of vectorial free boundary problems. It turns out that the polygonal version of this inequality, very easy to state, is extremely hard to prove and remains open since 1947, when it was conjectured by Polya. I will connect this question to somehow easier problems, like polygonal versions of Hardy-Littlewood and Riesz inequalities and I will discuss the local minimality of regular polygons and the possibility to prove the conjecture by a mixed approach. This talk is based on joint works with Beniamin Bogosel and Ilaria Fragala.
[ Reference URL ]The starting point is the Faber-Krahn inequality on the first eigenvalue of the Dirichlet Laplacian. Many refinements were obtained in the last years, mainly due to the use of recent techniques based on the analysis of vectorial free boundary problems. It turns out that the polygonal version of this inequality, very easy to state, is extremely hard to prove and remains open since 1947, when it was conjectured by Polya. I will connect this question to somehow easier problems, like polygonal versions of Hardy-Littlewood and Riesz inequalities and I will discuss the local minimality of regular polygons and the possibility to prove the conjecture by a mixed approach. This talk is based on joint works with Beniamin Bogosel and Ilaria Fragala.
https://sites.google.com/g.ecc.u-tokyo.ac.jp/utnas-bulletin-board/
2025/12/08
Seminar on Geometric Complex Analysis
10:30-12:00 Room #128 (Graduate School of Math. Sci. Bldg.)
Rei Murakami (Tohoku Univ.)
. (Japanese)
[ Reference URL ]
https://forms.gle/gTP8qNZwPyQyxjTj8
Rei Murakami (Tohoku Univ.)
. (Japanese)
[ Reference URL ]
https://forms.gle/gTP8qNZwPyQyxjTj8
2025/12/03
Number Theory Seminar
17:00-18:00 Room #117 (Graduate School of Math. Sci. Bldg.)
Takato Watanabe (University of Tokyo)
On p-adic Galois representations of monomial fields and p-adic differential modules on fake annuli
Takato Watanabe (University of Tokyo)
On p-adic Galois representations of monomial fields and p-adic differential modules on fake annuli
[ Abstract ]
The fake annuli introduced by Kedlaya are certain one-dimensional subannuli of p-adic polyannuli with multiple derivations. They are related to monomial fields, which are generalizations of Laurent series fields over fields of characteristic p. We compare the arithmetic and differential Swan conductors of rank one p-adic Galois representations of monomial fields with finite local monodromy. We also introduce a p-adic counterpart of monomial fields and explain generalizations of classical results to this setting, such as the overconvergence of p-adic Galois representations, and Berger’s construction of p-adic differential modules from de Rham ones.
The fake annuli introduced by Kedlaya are certain one-dimensional subannuli of p-adic polyannuli with multiple derivations. They are related to monomial fields, which are generalizations of Laurent series fields over fields of characteristic p. We compare the arithmetic and differential Swan conductors of rank one p-adic Galois representations of monomial fields with finite local monodromy. We also introduce a p-adic counterpart of monomial fields and explain generalizations of classical results to this setting, such as the overconvergence of p-adic Galois representations, and Berger’s construction of p-adic differential modules from de Rham ones.
2025/12/02
Tuesday Seminar of Analysis
16:00-17:30 Room # 002 (Graduate School of Math. Sci. Bldg.)
Yusuke OKA (The University of Tokyo)
On the solvability of fractional semilinear heat equations with distributional inhomogeneous terms (Japanese)
Yusuke OKA (The University of Tokyo)
On the solvability of fractional semilinear heat equations with distributional inhomogeneous terms (Japanese)
Tuesday Seminar on Topology
17:30-18:30 Room #hybrid/056 (Graduate School of Math. Sci. Bldg.)
Pre-registration required. See our seminar webpage.
Shinpei Baba (University of Osaka)
Bending Teichmüller spaces and character varieties (JAPANESE)
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html
Pre-registration required. See our seminar webpage.
Shinpei Baba (University of Osaka)
Bending Teichmüller spaces and character varieties (JAPANESE)
[ Abstract ]
Let S be a closed oriented surface of genus at least two. The Teichmüller space of S can be regarded as the space of discrete faithful representations from the fundamental group of S into PSL(2, R). Given a simple closed curve on S with positive weight (or more generally, a measured lamination), we can "bend" the repsentation along the curve by an angle equal to the weight, and obtain a representation of the surface group into PSL(2, C). This bending deformation induces a mapping from the Teichmüller space into the space of representations of the surface group into PSL(2, C). We discuss some interesting properties of this mapping.
If time permits, we also discuss a complexification of this mapping.
[ Reference URL ]Let S be a closed oriented surface of genus at least two. The Teichmüller space of S can be regarded as the space of discrete faithful representations from the fundamental group of S into PSL(2, R). Given a simple closed curve on S with positive weight (or more generally, a measured lamination), we can "bend" the repsentation along the curve by an angle equal to the weight, and obtain a representation of the surface group into PSL(2, C). This bending deformation induces a mapping from the Teichmüller space into the space of representations of the surface group into PSL(2, C). We discuss some interesting properties of this mapping.
If time permits, we also discuss a complexification of this mapping.
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html
2025/12/01
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.
Mamoru Okamoto (Hiroshima University )
エネルギー臨界確率非線形Schrödinger方程式の大域解
We are having teatime from 15:15 in the common room on the second floor. Please join us.
Mamoru Okamoto (Hiroshima University )
エネルギー臨界確率非線形Schrödinger方程式の大域解
[ Abstract ]
確率非線形Schrödinger方程式の初期値問題を考える。空間3次元では5次の非線形項がエネルギー臨界である。本講演では、その場合のエネルギー空間における時間大域可解性について述べる。特に、トーラスにおけるSchrödinger方程式の平滑化作用の弱さやノイズ項に起因する問題点、それらをどのように克服するかに焦点を当てる。本講演の内容は、Guopeng Li氏 (Beijing Institute of Technology)、Liying Tao氏 (China Academy of Engineering Physics) との共同研究に基づく。
確率非線形Schrödinger方程式の初期値問題を考える。空間3次元では5次の非線形項がエネルギー臨界である。本講演では、その場合のエネルギー空間における時間大域可解性について述べる。特に、トーラスにおけるSchrödinger方程式の平滑化作用の弱さやノイズ項に起因する問題点、それらをどのように克服するかに焦点を当てる。本講演の内容は、Guopeng Li氏 (Beijing Institute of Technology)、Liying Tao氏 (China Academy of Engineering Physics) との共同研究に基づく。
2025/11/28
Algebraic Geometry Seminar
13:30-15:00 Room #118 (Graduate School of Math. Sci. Bldg.)
Fumiaki Suzuki (Peking University)
The integral Tate conjecture over finite fields and two coniveau filtrations
Fumiaki Suzuki (Peking University)
The integral Tate conjecture over finite fields and two coniveau filtrations
[ Abstract ]
We construct a new type of counterexamples to the integral Tate conjecture over finite fields, where a geometric cycle map is surjective but an arithmetic cycle map is not. We also discuss the relation of this problem with two coniveau filtrations, and show some positive results toward a conjecture of Colliot-Thélène and Kahn. This is joint work with Federico Scavia.
We construct a new type of counterexamples to the integral Tate conjecture over finite fields, where a geometric cycle map is surjective but an arithmetic cycle map is not. We also discuss the relation of this problem with two coniveau filtrations, and show some positive results toward a conjecture of Colliot-Thélène and Kahn. This is joint work with Federico Scavia.
Logic
13:00-14:00 Room #122 (Graduate School of Math. Sci. Bldg.)
Ryuya Hora (The University of Tokyo)
Connectedness and full subcategories of topoi (Japanese)
Ryuya Hora (The University of Tokyo)
Connectedness and full subcategories of topoi (Japanese)
2025/11/27
Colloquium
15:30-16:30 Room #NISSAY Lecture Hall (大講義室) (Graduate School of Math. Sci. Bldg.)
Ahmed Abbes (IHES)
The p-adic Simpson correspondence (English)
Ahmed Abbes (IHES)
The p-adic Simpson correspondence (English)
[ Abstract ]
The classical Simpson correspondence describes complex linear representations of the fundamental group of a smooth complex projective variety in terms of linear algebra objects, namely Higgs bundles. Inspired by this, Faltings initiated in 2005 a p-adic analogue, aiming to understand continuous p-adic representations of the geometric fundamental group of a smooth projective variety over a p-adic local field. Although the formulation mirrors the complex case, the methods in the p-adic setting are entirely different and build on ideas from Sen theory and Faltings’ approach to p-adic Hodge theory.
In this talk, I will survey the p-adic Simpson correspondence with a focus on the construction developed jointly with M. Gros, and on more recent work with M. Gros and T. Tsuji. In this latter work, we develop a new framework for studying the functoriality of the correspondence. The key idea is a novel twisting technique for Higgs modules using Higgs-Tate algebras, which is inspired by our earlier approach and encompasses it as a special case. The resulting framework provides twisted pullbacks and higher direct images of Higgs modules, allowing us to study the functoriality of the p-adic Simpson correspondence under arbitrary pullbacks and proper (log)smooth direct images by morphisms that do not necessarily lift to the infinitesimal deformations of the varieties chosen to construct the p-adic Simpson correspondence. Along the way, we clarify the relation of our framework with recent developments involving line bundles on the spectral variety.
The classical Simpson correspondence describes complex linear representations of the fundamental group of a smooth complex projective variety in terms of linear algebra objects, namely Higgs bundles. Inspired by this, Faltings initiated in 2005 a p-adic analogue, aiming to understand continuous p-adic representations of the geometric fundamental group of a smooth projective variety over a p-adic local field. Although the formulation mirrors the complex case, the methods in the p-adic setting are entirely different and build on ideas from Sen theory and Faltings’ approach to p-adic Hodge theory.
In this talk, I will survey the p-adic Simpson correspondence with a focus on the construction developed jointly with M. Gros, and on more recent work with M. Gros and T. Tsuji. In this latter work, we develop a new framework for studying the functoriality of the correspondence. The key idea is a novel twisting technique for Higgs modules using Higgs-Tate algebras, which is inspired by our earlier approach and encompasses it as a special case. The resulting framework provides twisted pullbacks and higher direct images of Higgs modules, allowing us to study the functoriality of the p-adic Simpson correspondence under arbitrary pullbacks and proper (log)smooth direct images by morphisms that do not necessarily lift to the infinitesimal deformations of the varieties chosen to construct the p-adic Simpson correspondence. Along the way, we clarify the relation of our framework with recent developments involving line bundles on the spectral variety.
2025/11/25
Numerical Analysis Seminar
16:30-18:00 Room #117 (Graduate School of Math. Sci. Bldg.)
Lars Diening (Bielefeld University)
Sobolev stability of the $L^2$-projection (English)
https://sites.google.com/g.ecc.u-tokyo.ac.jp/utnas-bulletin-board/
Lars Diening (Bielefeld University)
Sobolev stability of the $L^2$-projection (English)
[ Abstract ]
We prove the $W^{1,2}$-stability of the $L^2$-projection on Lagrange elements for adaptive meshes and arbitrary polynomial degree. This property is especially important for the numerical analysis of parabolic problems. We will explain that the stability of the projection is connected to the grading constants of the underlying adaptive refinement routine. For arbitrary dimensions, we show that the bisection algorithm of Maubach and Traxler produces meshes with a grading constant 2. This implies $W^{1,2}$-stability of the $L^2$-projection up to dimension six.
[ Reference URL ]We prove the $W^{1,2}$-stability of the $L^2$-projection on Lagrange elements for adaptive meshes and arbitrary polynomial degree. This property is especially important for the numerical analysis of parabolic problems. We will explain that the stability of the projection is connected to the grading constants of the underlying adaptive refinement routine. For arbitrary dimensions, we show that the bisection algorithm of Maubach and Traxler produces meshes with a grading constant 2. This implies $W^{1,2}$-stability of the $L^2$-projection up to dimension six.
https://sites.google.com/g.ecc.u-tokyo.ac.jp/utnas-bulletin-board/
Tuesday Seminar on Topology
17:00-18:00 Online
Pre-registration required. See our seminar webpage.
Katsuhiko Kuribayashi (Shinshu University)
Interleavings of persistence dg-modules and Sullivan models for maps (JAPANESE)
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html
Pre-registration required. See our seminar webpage.
Katsuhiko Kuribayashi (Shinshu University)
Interleavings of persistence dg-modules and Sullivan models for maps (JAPANESE)
[ Abstract ]
The cohomology interleaving distance (CohID) is introduced and considered in the category of persistence differential graded modules. As a consequence, we show that, in the category, the distance coincides with the the homotopy commutative interleaving distance, the homotopy interleaving distance originally due to Blumberg and Lesnick, and the interleaving distance in the homotopy category (IDHC) in the sense of Lanari and Scoccola. Moreover, by applying the CohID to spaces over the classifying space of the circle group via the singular cochain functor, we have a numerical two-variable homotopy invariant for such spaces. In the latter half of the talk, we consider extended tame persistence commutative differential graded algebras (CDGA) associated with relative Sullivan algebras. Then, the IDHC enables us to introduce an extended pseudodistance between continuous maps with such persistence objects. By examining the pseudodistance, we see that the persistence CDGA is more `sensitive' than the persistence homology. This talk is based on joint work with Naito, Sekizuka, Wakatsuki and Yamaguchi.
[ Reference URL ]The cohomology interleaving distance (CohID) is introduced and considered in the category of persistence differential graded modules. As a consequence, we show that, in the category, the distance coincides with the the homotopy commutative interleaving distance, the homotopy interleaving distance originally due to Blumberg and Lesnick, and the interleaving distance in the homotopy category (IDHC) in the sense of Lanari and Scoccola. Moreover, by applying the CohID to spaces over the classifying space of the circle group via the singular cochain functor, we have a numerical two-variable homotopy invariant for such spaces. In the latter half of the talk, we consider extended tame persistence commutative differential graded algebras (CDGA) associated with relative Sullivan algebras. Then, the IDHC enables us to introduce an extended pseudodistance between continuous maps with such persistence objects. By examining the pseudodistance, we see that the persistence CDGA is more `sensitive' than the persistence homology. This talk is based on joint work with Naito, Sekizuka, Wakatsuki and Yamaguchi.
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html
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