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Seminar information archive
Seminar information archive ～02/03｜Today's seminar 02/04 | Future seminars 02/05～
Tuesday Seminar on Topology
17:30-18:30 Room #hybrid/056 (Graduate School of Math. Sci. Bldg.)
Pre-registration required. See our seminar webpage.
Masaki Tsukamoto (Kyoto University)
Rate distortion dimension of random Brody curves (JAPANESE)
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html
Pre-registration required. See our seminar webpage.
Masaki Tsukamoto (Kyoto University)
Rate distortion dimension of random Brody curves (JAPANESE)
[ Abstract ]
Brody curves are one-Lipschtiz holomorphic maps from the complex plane to the complex projective space. Entire holomorphic curves have been studied over a century since Nevanlinna and H. Cartan, but there still remain many fundamental questions. In this talk we explain that ideas of ergodic theory and geometric measure theory provide a radically new approach on them. Roughly speaking, we show that Brody curves have an ergodic theoretic structure somehow analogous to that of Axiom A diffeomorphisms. In particular we establish "Ruelle inequality" and "existence of equilibrium measures" for Brody curves.
[ Reference URL ]Brody curves are one-Lipschtiz holomorphic maps from the complex plane to the complex projective space. Entire holomorphic curves have been studied over a century since Nevanlinna and H. Cartan, but there still remain many fundamental questions. In this talk we explain that ideas of ergodic theory and geometric measure theory provide a radically new approach on them. Roughly speaking, we show that Brody curves have an ergodic theoretic structure somehow analogous to that of Axiom A diffeomorphisms. In particular we establish "Ruelle inequality" and "existence of equilibrium measures" for Brody curves.
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html
Lie Groups and Representation Theory
17:00-18:00 Room #118 (Graduate School of Math. Sci. Bldg.)
Robin van Haastrecht (Chalmers University of Technology/University of Gothenburg)
Wehrl-type inequalities for the holomorphic discrete series
(English)
Robin van Haastrecht (Chalmers University of Technology/University of Gothenburg)
Wehrl-type inequalities for the holomorphic discrete series
(English)
[ Abstract ]
Wehrl first investigated Wehrl-type inequalities while studying entropy in quantum mechanics. They can be formulated as inequalities of integrals of matrix coefficients of Lie groups, and the main question is to find states with minimal entropy. In this talk we prove $L^2$-$L^p$ Wehrl-type inequalities for the holomorphic discrete series representations of semisimple Lie groups. We find the best constants for inequalities and characterize the maximizers for even integers. This is joint work with Genkai Zhang.
Wehrl first investigated Wehrl-type inequalities while studying entropy in quantum mechanics. They can be formulated as inequalities of integrals of matrix coefficients of Lie groups, and the main question is to find states with minimal entropy. In this talk we prove $L^2$-$L^p$ Wehrl-type inequalities for the holomorphic discrete series representations of semisimple Lie groups. We find the best constants for inequalities and characterize the maximizers for even integers. This is joint work with Genkai Zhang.
2025/11/17
Seminar on Geometric Complex Analysis
10:30-12:00 Room #128 (Graduate School of Math. Sci. Bldg.)
Masanori Adachi (Shizuoka Univ.)
(Japanese)
[ Reference URL ]
https://forms.gle/gTP8qNZwPyQyxjTj8
Masanori Adachi (Shizuoka Univ.)
(Japanese)
[ Reference URL ]
https://forms.gle/gTP8qNZwPyQyxjTj8
Tokyo-Nagoya Algebra Seminar
16:30-18:00 Online
Yuto Moriwaki (RIKEN)
共形場理論の数学的定式化について (Japanese)
[ Reference URL ]
https://www.math.nagoya-u.ac.jp/~aaron.chan/TNAseminar.html
Yuto Moriwaki (RIKEN)
共形場理論の数学的定式化について (Japanese)
[ Reference URL ]
https://www.math.nagoya-u.ac.jp/~aaron.chan/TNAseminar.html
2025/11/12
FJ-LMI Seminar
15:00-15:40 Room #056 (Graduate School of Math. Sci. Bldg.)
Thomas Karam (Shanghai Jiao Tong University)
Contributions of information theory to pure mathematics (英語)
Thomas Karam (Shanghai Jiao Tong University)
Contributions of information theory to pure mathematics (英語)
[ Abstract ]
This talk will provide an overview of a mini-course to be taught in January 2026 at the University of Tokyo, aimed at describing how Shannon entropy, a tool that was originally developed for and motivated by a rigorous mathematical analysis of communications engineering, later led to developments that can to some extent be viewed as taking place in a converse direction, where Shannon entropy provided insight into central basic questions in several fields of pure mathematics.
This talk will provide an overview of a mini-course to be taught in January 2026 at the University of Tokyo, aimed at describing how Shannon entropy, a tool that was originally developed for and motivated by a rigorous mathematical analysis of communications engineering, later led to developments that can to some extent be viewed as taking place in a converse direction, where Shannon entropy provided insight into central basic questions in several fields of pure mathematics.
Seminar on Probability and Statistics
10:30-11:40 Room #126 (Graduate School of Math. Sci. Bldg.)
Lars Winkelmann (Free University of Berlin)
Testing the Maximal Rank of Time-Varying Covariance Matrices in Noisy High-Frequency Data (English)
https://u-tokyo-ac-jp.zoom.us/meeting/register/eRqQutp7TTeKmqH2Vhm8Xg
Lars Winkelmann (Free University of Berlin)
Testing the Maximal Rank of Time-Varying Covariance Matrices in Noisy High-Frequency Data (English)
[ Abstract ]
We address the problem of testing the maximal rank of time-varying covariance matrices in high-frequency diffusion models observed with additive noise. Building on a spectral representation of the quadratic covariation operator, we construct test statistics based on empirical eigenvalues of localized spectral covariance matrices. The presence of observational noise and the rotation of the eigenspace introduce a fundamental bias-variance trade-off. We derive the optimal separation rate at which the tests retain power, showing its dependence on both the smoothness of the covariance process and the existence of a spectral gap. Our theoretical framework integrates matrix perturbation theory, concentration inequalities, and statistical lower bound approaches. Simulations illustrate the performance of our methods, and an application to portfolios of government bonds underscores their practical relevance in financial econometrics.
[ Reference URL ]We address the problem of testing the maximal rank of time-varying covariance matrices in high-frequency diffusion models observed with additive noise. Building on a spectral representation of the quadratic covariation operator, we construct test statistics based on empirical eigenvalues of localized spectral covariance matrices. The presence of observational noise and the rotation of the eigenspace introduce a fundamental bias-variance trade-off. We derive the optimal separation rate at which the tests retain power, showing its dependence on both the smoothness of the covariance process and the existence of a spectral gap. Our theoretical framework integrates matrix perturbation theory, concentration inequalities, and statistical lower bound approaches. Simulations illustrate the performance of our methods, and an application to portfolios of government bonds underscores their practical relevance in financial econometrics.
https://u-tokyo-ac-jp.zoom.us/meeting/register/eRqQutp7TTeKmqH2Vhm8Xg
FJ-LMI Seminar
15:45-16:20 Room #056 (Graduate School of Math. Sci. Bldg.)
Raphaël LEFEVERE (Université de Paris Cité)
Macroscopic diffusion in random lattice Lorentz gases (英語)
https://fj-lmi.cnrs.fr/seminars/
Raphaël LEFEVERE (Université de Paris Cité)
Macroscopic diffusion in random lattice Lorentz gases (英語)
[ Abstract ]
I will present the general issues that have to be tackled when deriving macroscopic laws from microscopic deterministic laws of motion and a toy model where these issues may be solved.
[ Reference URL ]I will present the general issues that have to be tackled when deriving macroscopic laws from microscopic deterministic laws of motion and a toy model where these issues may be solved.
https://fj-lmi.cnrs.fr/seminars/
2025/11/11
Tuesday Seminar on Topology
9:30-10:30 Online
Pre-registration required. See our seminar webpage.
Richard Hain (Duke University)
Mapping class group actions on the homology of configuration spaces (ENGLISH)
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html
Pre-registration required. See our seminar webpage.
Richard Hain (Duke University)
Mapping class group actions on the homology of configuration spaces (ENGLISH)
[ Abstract ]
The action of the mapping class group of a surface S on the homology of the space F_n(S) of ordered configurations of n points in S is well understood when S has genus 0, but is not very well understood when S has positive genus. In this talk I will report on joint work with Clément Dupont (Montpellier) in the case where S is a surface of finite type of genus at least 2. We give a strong lower bound on the size of the Zariski closure of the image of the Torelli and mapping class groups in the automorphism group of the degree n cohomology of F_n(S). Our main tools are Hodge theory and the Goldman Lie algebra of the surface, which is the free abelian group generated by the conjugacy classes in the fundamental group of S.
[ Reference URL ]The action of the mapping class group of a surface S on the homology of the space F_n(S) of ordered configurations of n points in S is well understood when S has genus 0, but is not very well understood when S has positive genus. In this talk I will report on joint work with Clément Dupont (Montpellier) in the case where S is a surface of finite type of genus at least 2. We give a strong lower bound on the size of the Zariski closure of the image of the Torelli and mapping class groups in the automorphism group of the degree n cohomology of F_n(S). Our main tools are Hodge theory and the Goldman Lie algebra of the surface, which is the free abelian group generated by the conjugacy classes in the fundamental group of S.
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html
Tuesday Seminar on Topology
17:00-18:30 Room #hybrid/056 (Graduate School of Math. Sci. Bldg.)
Pre-registration required. See our seminar webpage.
Serban Matei Mihalache (The University of Tokyo)
Constructing solution of Polygon and Simplex equation (JAPANESE)
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html
Pre-registration required. See our seminar webpage.
Serban Matei Mihalache (The University of Tokyo)
Constructing solution of Polygon and Simplex equation (JAPANESE)
[ Abstract ]
The Polygon equation, formulated by Dimakis and Müller-Hoissen, can be interpreted as an algebraic equation corresponding to the Pachner (⌊(n+1)/2⌋+1, ⌈(n+1)/2⌉)-move on triangulations of n-dimensional PL manifolds, and is expected that this can be used to construct invariants of PL manifolds. In this talk, we show that solutions of higher-dimensional Polygon equations can be constructed from collections of "commutative" solutions of lower-dimensional Polygon equations, and we present explicit examples of such solutions. Furthermore, when a pair of solutions of the Polygon equation satisfies a condition called the mixed relation, we show that it gives rise to a solution of the Simplex equation, which is a higher-dimensional analogue of the Yang–Baxter equation. This talk is based on joint work with Tomoro Mochida.
[ Reference URL ]The Polygon equation, formulated by Dimakis and Müller-Hoissen, can be interpreted as an algebraic equation corresponding to the Pachner (⌊(n+1)/2⌋+1, ⌈(n+1)/2⌉)-move on triangulations of n-dimensional PL manifolds, and is expected that this can be used to construct invariants of PL manifolds. In this talk, we show that solutions of higher-dimensional Polygon equations can be constructed from collections of "commutative" solutions of lower-dimensional Polygon equations, and we present explicit examples of such solutions. Furthermore, when a pair of solutions of the Polygon equation satisfies a condition called the mixed relation, we show that it gives rise to a solution of the Simplex equation, which is a higher-dimensional analogue of the Yang–Baxter equation. This talk is based on joint work with Tomoro Mochida.
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html
Operator Algebra Seminars
16:45-18:15 Room #126 (Graduate School of Math. Sci. Bldg.)
Valerio Proietti (Univ. Oslo)
Base change, groupoid homology, and hyperbolic dynamics
[ Reference URL ]
https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm
Valerio Proietti (Univ. Oslo)
Base change, groupoid homology, and hyperbolic dynamics
[ Reference URL ]
https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm
2025/11/10
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.
Yushi Hamaguchi (Kyoto University)
確率ヴォルテラ方程式のマルコフリフトの弱エルゴード性
We are having teatime from 15:15 in the common room on the second floor. Please join us.
Yushi Hamaguchi (Kyoto University)
確率ヴォルテラ方程式のマルコフリフトの弱エルゴード性
[ Abstract ]
確率ヴォルテラ方程式の解は一般に非マルコフかつ非セミマルチンゲールであるような(有限次元)確率過程であるが、無限次元空間への持ち上げを考えることで、あるヒルベルト空間上のマルコフ過程(マルコフリフト)が得られる。
また、元の確率ヴォルテラ方程式の解は、このマルコフリフトのある種の射影として復元できる。
本研究の目的は、マルコフリフトの長時間漸近挙動を調べ、元の確率ヴォルテラ方程式の解に関する極限定理を得ることである。
そのうえで解決すべき難点は、マルコフリフトが満たす確率発展方程式が退化型であること、すなわち状態空間は無限次元であるが、ノイズを駆動するブラウン運動は有限次元であるという点である。
前回の東京確率論セミナー(2023年6月19日)では、マルコフリフトの漸近的対数ハルナック不等式、特に不変確率測度の一意性に関する結果を報告した。
本講演では、マルコフリフトの不変確率測度の存在性と指数型弱エルゴ―ド評価について、現在までに得られた研究成果を報告する。
確率ヴォルテラ方程式の解は一般に非マルコフかつ非セミマルチンゲールであるような(有限次元)確率過程であるが、無限次元空間への持ち上げを考えることで、あるヒルベルト空間上のマルコフ過程(マルコフリフト)が得られる。
また、元の確率ヴォルテラ方程式の解は、このマルコフリフトのある種の射影として復元できる。
本研究の目的は、マルコフリフトの長時間漸近挙動を調べ、元の確率ヴォルテラ方程式の解に関する極限定理を得ることである。
そのうえで解決すべき難点は、マルコフリフトが満たす確率発展方程式が退化型であること、すなわち状態空間は無限次元であるが、ノイズを駆動するブラウン運動は有限次元であるという点である。
前回の東京確率論セミナー(2023年6月19日)では、マルコフリフトの漸近的対数ハルナック不等式、特に不変確率測度の一意性に関する結果を報告した。
本講演では、マルコフリフトの不変確率測度の存在性と指数型弱エルゴ―ド評価について、現在までに得られた研究成果を報告する。
2025/11/06
Tokyo Probability Seminar
14:00-17:30 Room #128 (Graduate School of Math. Sci. Bldg.)
The lecture is on Thursday and start earlier. The classroom is 128. No teatime today.
Mo Dick Wong (Durham University) 14:00-15:30
On the limiting distribution of partial sums of random multiplicative functions
de Finetti Random Walks on a Hypercube and Gaussian Fields
The lecture is on Thursday and start earlier. The classroom is 128. No teatime today.
Mo Dick Wong (Durham University) 14:00-15:30
On the limiting distribution of partial sums of random multiplicative functions
[ Abstract ]
Consider a random walk associated with a Steinhaus multiplicative function (i.e. the increments are completely multiplicative and uniformly distributed on the complex unit circle): what can we say about its asymptotic behaviour? In his seminal work, Harper resolved a conjecture of Helson by showing that low fractional moments exhibit better-than-square-root cancellation, but the asymptotic distribution remained a mystery and was left as an open problem. In this talk, I will first explain some history and the number-theoretic motivations behind this model, and then present a central limit theorem that features a nonstandard renormalisation as well as a random variance described by the Riemann Zeta function on the critical line. I will highlight the probabilistic aspects of our proof, and in particular discuss a universality result for critical non-Gaussian multiplicative chaos. This is based on joint work with Ofir Gorodetsky.
Robert Griffiths (Monash University) 16:00-17:30Consider a random walk associated with a Steinhaus multiplicative function (i.e. the increments are completely multiplicative and uniformly distributed on the complex unit circle): what can we say about its asymptotic behaviour? In his seminal work, Harper resolved a conjecture of Helson by showing that low fractional moments exhibit better-than-square-root cancellation, but the asymptotic distribution remained a mystery and was left as an open problem. In this talk, I will first explain some history and the number-theoretic motivations behind this model, and then present a central limit theorem that features a nonstandard renormalisation as well as a random variance described by the Riemann Zeta function on the critical line. I will highlight the probabilistic aspects of our proof, and in particular discuss a universality result for critical non-Gaussian multiplicative chaos. This is based on joint work with Ofir Gorodetsky.
de Finetti Random Walks on a Hypercube and Gaussian Fields
[ Abstract ]
This talk will discuss a random walk on the infinite hypercube,
Xt+1 = Xt + Zt mod 2.
The increments (Zt) are i.i.d. with entries that form an infinite exchange- able {0,1} sequence, a de Finetti sequence. There is geometric killing in the random walk. A Gaussian free field (gx)x∈{0,1}∞ is associated with the random walk by taking the covariance function to be proportional to the Green function of the random walk. The Green function and a strong rep- resentation for (gx) are characterized by a negative binomial point process which involves the de Finetti measure of the increments of the random walk.
This talk will discuss a random walk on the infinite hypercube,
Xt+1 = Xt + Zt mod 2.
The increments (Zt) are i.i.d. with entries that form an infinite exchange- able {0,1} sequence, a de Finetti sequence. There is geometric killing in the random walk. A Gaussian free field (gx)x∈{0,1}∞ is associated with the random walk by taking the covariance function to be proportional to the Green function of the random walk. The Green function and a strong rep- resentation for (gx) are characterized by a negative binomial point process which involves the de Finetti measure of the increments of the random walk.
2025/11/04
Tuesday Seminar on Topology
17:00-18:00 Online
Pre-registration required. See our seminar webpage.
Kazuto Takao (Tohoku University)
Diagrammatic criteria for strong irreducibility of Heegaard splittings and finiteness of Goeritz groups (JAPANESE)
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html
Pre-registration required. See our seminar webpage.
Kazuto Takao (Tohoku University)
Diagrammatic criteria for strong irreducibility of Heegaard splittings and finiteness of Goeritz groups (JAPANESE)
[ Abstract ]
Casson-Gordon gave a criterion for Heegaard splittings of 3-manifolds to be strongly irreducible. By strengthening it, Lustig-Moriah gave a criterion for Goeritz groups of Heegaard splittings to be finite. Their criteria are based on Heegaard diagrams formed by maximal disk systems of the handlebodies. We generalize them for arbitrary disk systems, including minimal ones. As an application, we give Heegaard splittings with non-minimal genera and finite Goeritz groups. This is based on joint work with Yuya Koda.
[ Reference URL ]Casson-Gordon gave a criterion for Heegaard splittings of 3-manifolds to be strongly irreducible. By strengthening it, Lustig-Moriah gave a criterion for Goeritz groups of Heegaard splittings to be finite. Their criteria are based on Heegaard diagrams formed by maximal disk systems of the handlebodies. We generalize them for arbitrary disk systems, including minimal ones. As an application, we give Heegaard splittings with non-minimal genera and finite Goeritz groups. This is based on joint work with Yuya Koda.
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html
Number Theory Seminar
17:00-18:00 Room #117 (Graduate School of Math. Sci. Bldg.)
Ryomei Iwasa (University of Copenhagen)
Descent and pro-excision
Ryomei Iwasa (University of Copenhagen)
Descent and pro-excision
[ Abstract ]
The theme of this talk is descent and excision of cohomology theories of schemes. We will start with a discussion of the canonical topology on spectral schemes. Unlike on classical schemes, this topology includes many other types of covers, such as h-covers. Then I will explain that THH and TC satisfy descent with respect to the canonical topology, which generalizes the flat descent by Bhatt—Morrow—Scholze. This in turn implies the cdh descent of K-theory on spectral schemes, despite its failure on classical schemes. Furthermore, this implies the cdh pro-excision of K-theory on spectral schemes, which generalizes the derived case by Kelly—Saito—Tamme (the original noetherian case is due to Kerz—Strunk—Tamme). Our proof of the cdh pro-excision is quite different from the previous ones and is more algebraic in nature. The results presented here are based on discussions with Antieau, Burklund, and Krause.
The theme of this talk is descent and excision of cohomology theories of schemes. We will start with a discussion of the canonical topology on spectral schemes. Unlike on classical schemes, this topology includes many other types of covers, such as h-covers. Then I will explain that THH and TC satisfy descent with respect to the canonical topology, which generalizes the flat descent by Bhatt—Morrow—Scholze. This in turn implies the cdh descent of K-theory on spectral schemes, despite its failure on classical schemes. Furthermore, this implies the cdh pro-excision of K-theory on spectral schemes, which generalizes the derived case by Kelly—Saito—Tamme (the original noetherian case is due to Kerz—Strunk—Tamme). Our proof of the cdh pro-excision is quite different from the previous ones and is more algebraic in nature. The results presented here are based on discussions with Antieau, Burklund, and Krause.
Operator Algebra Seminars
16:45-18:15 Room #126 (Graduate School of Math. Sci. Bldg.)
Jesse Reimann (TU Delft)
Split exact sequences and KK-equivalences of quantum flag manifolds
[ Reference URL ]
https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm
Jesse Reimann (TU Delft)
Split exact sequences and KK-equivalences of quantum flag manifolds
[ Reference URL ]
https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm
2025/10/31
Algebraic Geometry Seminar
13:00-14:30 Room #118 (Graduate School of Math. Sci. Bldg.)
Miguel Angel Barja (UPC-Barcelona)
Asymptotic and continuous constructions in the geography of fibred varieties
Miguel Angel Barja (UPC-Barcelona)
Asymptotic and continuous constructions in the geography of fibred varieties
[ Abstract ]
Given a fibred variety $X$ onto a smooth variety $T$ it is possible to consider different types of inequalities between birational invariants associated to a line bundle $L$, such as Noether, Slope or Severi inequalities. Most of these inequalities are closely related through asymptotic constructions and/or continuous functions that suggest the use of some new invariants. We will survey different constructions both in characteristic 0 and positive characteristic, and will focus in the case of varieties of maximal Albanese dimension, fibred over curves. If time permits, we will also give some ideas on fibrations over surfaces.
Given a fibred variety $X$ onto a smooth variety $T$ it is possible to consider different types of inequalities between birational invariants associated to a line bundle $L$, such as Noether, Slope or Severi inequalities. Most of these inequalities are closely related through asymptotic constructions and/or continuous functions that suggest the use of some new invariants. We will survey different constructions both in characteristic 0 and positive characteristic, and will focus in the case of varieties of maximal Albanese dimension, fibred over curves. If time permits, we will also give some ideas on fibrations over surfaces.
Algebraic Geometry Seminar
15:00-16:30 Room #118 (Graduate School of Math. Sci. Bldg.)
Masafumi Hattori (University of Nottingham)
Normal stable degeneration of Noether-Horikawa surfaces: Deformation Part
Masafumi Hattori (University of Nottingham)
Normal stable degeneration of Noether-Horikawa surfaces: Deformation Part
[ Abstract ]
Koll’ar and Shepherd-Barron constructed a general theory for a canonical geometric compactification of moduli of smooth surfaces with ample canonical class by adding degenerations with only semi log canonical singularities. Their moduli is now called the KSBA moduli and degenerations are called stable degenerations. It has been a long standing question to classify all stable degenerations for smooth canonically polarized surfaces. In this talk, we focus on Q-Gorenstein deformation theory on Horikawa surfaces, which are minimal surfaces of general type in the case where the Noether inequality $K^2\geq 2p_g-4$ is an equality. This talk is based on the joint work (arXiv:2507:17633) with Hiroto Akaike, Makoto Enokizono, and Yuki Koto.
Koll’ar and Shepherd-Barron constructed a general theory for a canonical geometric compactification of moduli of smooth surfaces with ample canonical class by adding degenerations with only semi log canonical singularities. Their moduli is now called the KSBA moduli and degenerations are called stable degenerations. It has been a long standing question to classify all stable degenerations for smooth canonically polarized surfaces. In this talk, we focus on Q-Gorenstein deformation theory on Horikawa surfaces, which are minimal surfaces of general type in the case where the Noether inequality $K^2\geq 2p_g-4$ is an equality. This talk is based on the joint work (arXiv:2507:17633) with Hiroto Akaike, Makoto Enokizono, and Yuki Koto.
2025/10/29
Geometric Analysis Seminar
13:30-14:30 Room #126 (Graduate School of Math. Sci. Bldg.)
Tommaso Rossi (Scuola Internazionale Superiore di Studi Avanzati)
On the rectifiability of metric measure spaces with lower Ricci curvature bounds (英語)
https://sites.google.com/view/tommasorossi/home-page
Tommaso Rossi (Scuola Internazionale Superiore di Studi Avanzati)
On the rectifiability of metric measure spaces with lower Ricci curvature bounds (英語)
[ Abstract ]
Given a metric measure space (X,d,m), the curvature-dimension condition CD(K,N), and the measure contraction property MCP(K,N), are synthetic notions of having Ricci curvature bounded below by K (and dimension bounded above by N). We prove some rectifiability results for CD(K,N) and MCP(K,N) metric measure spaces (X,d,m) with pointwise Ahlfors regular reference measure m and with m-almost everywhere unique metric tangents. Our strategy is based on the failure of the CD condition in sub-Finsler Carnot groups, on a new result on the failure of the non-collapsed MCP on sub-Finsler Carnot groups, and on a recent breakthrough by D. Bate. This is a joint work with M. Magnabosco and A. Mondino.
[ Reference URL ]Given a metric measure space (X,d,m), the curvature-dimension condition CD(K,N), and the measure contraction property MCP(K,N), are synthetic notions of having Ricci curvature bounded below by K (and dimension bounded above by N). We prove some rectifiability results for CD(K,N) and MCP(K,N) metric measure spaces (X,d,m) with pointwise Ahlfors regular reference measure m and with m-almost everywhere unique metric tangents. Our strategy is based on the failure of the CD condition in sub-Finsler Carnot groups, on a new result on the failure of the non-collapsed MCP on sub-Finsler Carnot groups, and on a recent breakthrough by D. Bate. This is a joint work with M. Magnabosco and A. Mondino.
https://sites.google.com/view/tommasorossi/home-page
2025/10/28
Tuesday Seminar on Topology
17:00-18:30 Room #056 (Graduate School of Math. Sci. Bldg.)
Pre-registration required. See our seminar webpage.
Ayumu Inoue (Tsuda University)
On a relationship between quandle homology and relative group homology, from the view point of Seifert surfaces (JAPANESE)
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html
Pre-registration required. See our seminar webpage.
Ayumu Inoue (Tsuda University)
On a relationship between quandle homology and relative group homology, from the view point of Seifert surfaces (JAPANESE)
[ Abstract ]
Quandles and their homology are known to have good chemistry with knot theory. Associated with a triple of a group G, its automorphism, and its subgroup H satisfying a certain condition, we have a quandle. In this talk, we see that we have a chain map from the quandle chain complex of the quandle to the (Adamson/Hochschild) relative group chain complex of (G, H). We also see that this chain map has good chemistry with a triangulation of Seifert surface of a knot.
[ Reference URL ]Quandles and their homology are known to have good chemistry with knot theory. Associated with a triple of a group G, its automorphism, and its subgroup H satisfying a certain condition, we have a quandle. In this talk, we see that we have a chain map from the quandle chain complex of the quandle to the (Adamson/Hochschild) relative group chain complex of (G, H). We also see that this chain map has good chemistry with a triangulation of Seifert surface of a knot.
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html
Tuesday Seminar of Analysis
15:00-17:30 Room #002 (Graduate School of Math. Sci. Bldg.)
Lauri Särkiö (Aalto University) 15:00-16:00
Gradient higher integrability of parabolic double-phase equations (English)
Global well-posedness for 3D quadratic nonlinear Schrödinger equations (Japanese)
Lauri Särkiö (Aalto University) 15:00-16:00
Gradient higher integrability of parabolic double-phase equations (English)
[ Abstract ]
Elliptic double-phase problems have been studied extensively in the last decade since a series of results by Mingione and others. Recently several regularity results have been obtained also for parabolic double-phase equations, yet many questions remain unsolved. In this talk, we focus on gradient higher integrability, showing that solutions to parabolic double-phase equations belong to a slightly higher Sobolev class than assumed a priori. The talk is based on joint work with Wontae Kim, Juha Kinnunen and Kristian Moring.
Shinya Kinoshita (Nagoya University) 16:30-17:30Elliptic double-phase problems have been studied extensively in the last decade since a series of results by Mingione and others. Recently several regularity results have been obtained also for parabolic double-phase equations, yet many questions remain unsolved. In this talk, we focus on gradient higher integrability, showing that solutions to parabolic double-phase equations belong to a slightly higher Sobolev class than assumed a priori. The talk is based on joint work with Wontae Kim, Juha Kinnunen and Kristian Moring.
Global well-posedness for 3D quadratic nonlinear Schrödinger equations (Japanese)
[ Abstract ]
In this talk, we consider the Cauchy problem of the 3D nonlinear Schrödinger equations. It is known that if the nonlinearity is homogeneous of degree $p >2$, the general theory would provide the small data global existence of 3D NLS. In the quadratic case, which can be seen as a threshold of the small data global existence, the structure of nonlinearity plays a role and more sophisticated analysis is required. The aim in this talk is to show the global well-posedness in the scaling critical space with an additional angular regularity. The proof is based on the Fourier restriction norm method combined with several linear and bilinear estimates for the linear solutions.
In this talk, we consider the Cauchy problem of the 3D nonlinear Schrödinger equations. It is known that if the nonlinearity is homogeneous of degree $p >2$, the general theory would provide the small data global existence of 3D NLS. In the quadratic case, which can be seen as a threshold of the small data global existence, the structure of nonlinearity plays a role and more sophisticated analysis is required. The aim in this talk is to show the global well-posedness in the scaling critical space with an additional angular regularity. The proof is based on the Fourier restriction norm method combined with several linear and bilinear estimates for the linear solutions.
2025/10/27
Seminar on Geometric Complex Analysis
10:30-12:00 Room #128 (Graduate School of Math. Sci. Bldg.)
Shohei Ma (Institute of Science Tokyo)
. (Japanese)
[ Reference URL ]
https://forms.gle/gTP8qNZwPyQyxjTj8
Shohei Ma (Institute of Science Tokyo)
. (Japanese)
[ Reference URL ]
https://forms.gle/gTP8qNZwPyQyxjTj8
2025/10/21
FJ-LMI Seminar
16:00-16:40 Room #128 (Graduate School of Math. Sci. Bldg.)
Ramla ABDELLATIF (Université de Picardie)
Studying $p$-modular representations of $p$-adic groups in the setting of the Langlands programme (英語)
Ramla ABDELLATIF (Université de Picardie)
Studying $p$-modular representations of $p$-adic groups in the setting of the Langlands programme (英語)
[ Abstract ]
This talk aims to introduce the context of my primary research topic, namely $p$-modular representations of $p$-adic groups, as well as a current state of the art in the field, including some related questions I am currently exploring. After motivating the study of classical and modular Langlands correspondences for $p$-adic groups, I will explain why the $p$-modular setting (i.e. when representations of $p$-adic groups have coefficients in a field of positive characteristic equal to $p$) differs significantly from other settings (namely the complex and $\ell$-modular ones, with $\ell$ a prime distinct from $p$), then I will present the main results known so far about $p$-modular irreducible smooth representations of $p$-adic groups, with a particular focus on the special linear group $\mathrm{SL}_{2}$.
This talk aims to introduce the context of my primary research topic, namely $p$-modular representations of $p$-adic groups, as well as a current state of the art in the field, including some related questions I am currently exploring. After motivating the study of classical and modular Langlands correspondences for $p$-adic groups, I will explain why the $p$-modular setting (i.e. when representations of $p$-adic groups have coefficients in a field of positive characteristic equal to $p$) differs significantly from other settings (namely the complex and $\ell$-modular ones, with $\ell$ a prime distinct from $p$), then I will present the main results known so far about $p$-modular irreducible smooth representations of $p$-adic groups, with a particular focus on the special linear group $\mathrm{SL}_{2}$.
2025/10/20
Seminar on Geometric Complex Analysis
10:30-12:00 Room #128 (Graduate School of Math. Sci. Bldg.)
Hideyuki Ishi (Osaka Metropolitan Univ.)
A CR-Laplacian type operator for the Silov boundary of a homogeneous Siegel domain (Japanese)
https://forms.gle/gTP8qNZwPyQyxjTj8
Hideyuki Ishi (Osaka Metropolitan Univ.)
A CR-Laplacian type operator for the Silov boundary of a homogeneous Siegel domain (Japanese)
[ Abstract ]
Let $\Sigma$ be the Silov boundary of a homogeneous Siegel domain $D$ on which a Lie group $G$ acts transitively as affine transformations. The CR-structure on $\Sigma$ naturally induced from the ambient complex vector space is non-trivial if and only if $D$ is of non-tube type. In this case, $\Sigma$ is naturally identified with a two-step nilpotent Lie subgroup $N$ of $G$, called a generalized Heisenberg Lie group. Since the CR-structure is invariant under the action of $G$, the CR-cohomology space over $\Sigma$ can be regarded as a $G$-module. We consider unitarization of this presentation of $G$. The kernel of the CR-Laplacian does not give the solution because the natural Riemannian metric on $\Sigma$ is not $G$-invariant, so that the $G$-action does not preserve the space of CR-harmonic forms. Nevertheless, Nomura defined a unitary $G$-action on the space indirectly when $G$ is split solvable. In this talk, we introduce a space of CR-cochains with $G$-invariant inner product defined via the Fourier transform. Then the associated CR-operator is no longer a differential operator, while the kernel of the operator gives a unitarization of the representation of $G$ over the cohomology space.
[ Reference URL ]Let $\Sigma$ be the Silov boundary of a homogeneous Siegel domain $D$ on which a Lie group $G$ acts transitively as affine transformations. The CR-structure on $\Sigma$ naturally induced from the ambient complex vector space is non-trivial if and only if $D$ is of non-tube type. In this case, $\Sigma$ is naturally identified with a two-step nilpotent Lie subgroup $N$ of $G$, called a generalized Heisenberg Lie group. Since the CR-structure is invariant under the action of $G$, the CR-cohomology space over $\Sigma$ can be regarded as a $G$-module. We consider unitarization of this presentation of $G$. The kernel of the CR-Laplacian does not give the solution because the natural Riemannian metric on $\Sigma$ is not $G$-invariant, so that the $G$-action does not preserve the space of CR-harmonic forms. Nevertheless, Nomura defined a unitary $G$-action on the space indirectly when $G$ is split solvable. In this talk, we introduce a space of CR-cochains with $G$-invariant inner product defined via the Fourier transform. Then the associated CR-operator is no longer a differential operator, while the kernel of the operator gives a unitarization of the representation of $G$ over the cohomology space.
https://forms.gle/gTP8qNZwPyQyxjTj8
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.
Ryo Oizumi (National Institute of Population and Social Security Research)
Fredholm Integral Equations and Eigenstructure: Genealogical Expansions via Non–Hilbert–Schmidt Solutions
We are having teatime from 15:15 in the common room on the second floor. Please join us.
Ryo Oizumi (National Institute of Population and Social Security Research)
Fredholm Integral Equations and Eigenstructure: Genealogical Expansions via Non–Hilbert–Schmidt Solutions
[ Abstract ]
Fredholm integral equations play a central role in describing the long-term behavior of structured population models. In this talk, I present a determinant-free approach that constructs eigenfunctions through genealogical expansions, valid even beyond the Hilbert–Schmidt setting. The expansion is closely related to taboo probabilities in Markov chains, allowing eigenfunctions to be interpreted as cumulative ancestral contributions. As an application, I discuss age-structured branching processes and show how quantities such as expected generation counts and reproduction numbers naturally arise from the eigenvalue problem. This perspective highlights how eigenstructure encodes genealogical memory and opens connections between population dynamics, probability theory, and evolutionary processes.
Fredholm integral equations play a central role in describing the long-term behavior of structured population models. In this talk, I present a determinant-free approach that constructs eigenfunctions through genealogical expansions, valid even beyond the Hilbert–Schmidt setting. The expansion is closely related to taboo probabilities in Markov chains, allowing eigenfunctions to be interpreted as cumulative ancestral contributions. As an application, I discuss age-structured branching processes and show how quantities such as expected generation counts and reproduction numbers naturally arise from the eigenvalue problem. This perspective highlights how eigenstructure encodes genealogical memory and opens connections between population dynamics, probability theory, and evolutionary processes.
Tokyo-Nagoya Algebra Seminar
16:30-18:00 Online
Toshiya Yurikusa (Osaka Metropolitan University)
Finiteness and tameness of Jacobian algebras (Japanese)
https://www.math.nagoya-u.ac.jp/~aaron.chan/TNAseminar.html
Toshiya Yurikusa (Osaka Metropolitan University)
Finiteness and tameness of Jacobian algebras (Japanese)
[ Abstract ]
本講演では、有限次元ヤコビ代数をその表現型の観点から研究し、$E$不変量によって定義される$E$有限性および$E$-tame性と、$g$有限性、$\tau$傾有限性、表現有限性などの他の有限性・tame性の概念との対応について述べる。
まず、これらの性質がクイバーとポテンシャルの変異の下で不変であることを示す。その結果として、有限次元ヤコビ代数$\mathcal{J}(Q,W)$が$E$有限であることは、$g$有限、$\tau$傾有限、表現有限であることと同値であり、この場合には $Q$がDynkin型であることが分かる。この結果は、Demonetの「$E$有限なら$g$有限である」という予想を含む形で成立している。
また、$E$-tame性に関しては、例外的な3つの型を除いて、$g$-tame性および表現tame性と対応することが分かる。本講演は、Mohamad Haerizadeh氏との共同研究に基づくものである。
Zoom ID 829 2845 2592
Password 265160
[ Reference URL ]本講演では、有限次元ヤコビ代数をその表現型の観点から研究し、$E$不変量によって定義される$E$有限性および$E$-tame性と、$g$有限性、$\tau$傾有限性、表現有限性などの他の有限性・tame性の概念との対応について述べる。
まず、これらの性質がクイバーとポテンシャルの変異の下で不変であることを示す。その結果として、有限次元ヤコビ代数$\mathcal{J}(Q,W)$が$E$有限であることは、$g$有限、$\tau$傾有限、表現有限であることと同値であり、この場合には $Q$がDynkin型であることが分かる。この結果は、Demonetの「$E$有限なら$g$有限である」という予想を含む形で成立している。
また、$E$-tame性に関しては、例外的な3つの型を除いて、$g$-tame性および表現tame性と対応することが分かる。本講演は、Mohamad Haerizadeh氏との共同研究に基づくものである。
Zoom ID 829 2845 2592
Password 265160
https://www.math.nagoya-u.ac.jp/~aaron.chan/TNAseminar.html
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