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過去の記録 ～06/28｜本日 06/29 | 今後の予定 06/30～
2026年06月30日(火)
トポロジー火曜セミナー
16:00-17:30 数理科学研究科棟(駒場) hybrid/123号室
対面参加、オンライン参加のいずれの場合もセミナーのホームページから参加登録を行って下さい。
Sang-hyun Kim 氏 (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
対面参加、オンライン参加のいずれの場合もセミナーのホームページから参加登録を行って下さい。
Sang-hyun Kim 氏 (Korea Institute For Advanced Study)
Structure and rigidity of manifold diffeomorphism groups (ENGLISH)
[ 講演概要 ]
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).
[ 参考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年07月01日(水)
代数学コロキウム
17:00-18:00 数理科学研究科棟(駒場) 117号室
石倉麟太郎 氏 (東京大学大学院数理科学研究科)
On boundedness of the number of cuspidal automorphic representations of Mp(4) ordinary at p
石倉麟太郎 氏 (東京大学大学院数理科学研究科)
On boundedness of the number of cuspidal automorphic representations of Mp(4) ordinary at p
[ 講演概要 ]
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年07月03日(金)
代数幾何学セミナー
13:15-14:45 数理科学研究科棟(駒場) 117号室
吉川 翔 氏 (東京科学大学)
Hodge–Tate splitting and Akizuki–Nakano vanishing
吉川 翔 氏 (東京科学大学)
Hodge–Tate splitting and Akizuki–Nakano vanishing
[ 講演概要 ]
Akizuki–Nakano vanishing theorem は、Kodaira vanishing theorem を微分形式係数のコホモロジーへ拡張する基本的な消滅定理であり、複素代数幾何においてコホモロジーの制御や変形理論に重要な役割を果たす。一方、正標数ではこの定理は一般には成立せず、どのような幾何学的条件の下で同様の消滅定理が成り立つかは、自然かつ重要な問題である。
この方向の出発点として、Deligne–Illusie は、滑らかな固有多様体がW_2-lift をもち、かつその次元が標数より小さい場合に、de Rham complex の分解を用いて Akizuki–Nakano vanishing を証明した。近年、Petrov は quasi-F-split 多様体に対して、次元に関する制限なしに Akizuki–Nakano vanishing が従うことを証明した。
本講演では、これらの結果を統一的に捉える枠組みとして Hodge–Tate splitting という条件を考察し、この条件から Akizuki–Nakano vanishing が導かれることを説明する。また、この結果の混標数における類似についても紹介したい。
本講演は石塚彾氏との共同研究に基づく。
Akizuki–Nakano vanishing theorem は、Kodaira vanishing theorem を微分形式係数のコホモロジーへ拡張する基本的な消滅定理であり、複素代数幾何においてコホモロジーの制御や変形理論に重要な役割を果たす。一方、正標数ではこの定理は一般には成立せず、どのような幾何学的条件の下で同様の消滅定理が成り立つかは、自然かつ重要な問題である。
この方向の出発点として、Deligne–Illusie は、滑らかな固有多様体がW_2-lift をもち、かつその次元が標数より小さい場合に、de Rham complex の分解を用いて Akizuki–Nakano vanishing を証明した。近年、Petrov は quasi-F-split 多様体に対して、次元に関する制限なしに Akizuki–Nakano vanishing が従うことを証明した。
本講演では、これらの結果を統一的に捉える枠組みとして Hodge–Tate splitting という条件を考察し、この条件から Akizuki–Nakano vanishing が導かれることを説明する。また、この結果の混標数における類似についても紹介したい。
本講演は石塚彾氏との共同研究に基づく。
2026年07月06日(月)
複素解析幾何セミナー
10:30-12:00 数理科学研究科棟(駒場) 126号室
Xiaojun Wu 氏 (筑波大学)
Generalised Ueda Obstruction Classes and Non-Semipositive Line Bundles (English)
https://forms.gle/8ERsVDLuKHwbVzm57
Xiaojun Wu 氏 (筑波大学)
Generalised Ueda Obstruction Classes and Non-Semipositive Line Bundles (English)
[ 講演概要 ]
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.
[ 参考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
2026年07月07日(火)
作用素環セミナー
16:45-18:15 数理科学研究科棟(駒場) 126号室
橋本七海 氏 (慶応大)
Equivalence of categories of KK-theory or E-theory for $C^*$-algebras over topological spaces by reflection functors
[ 参考URL ]
https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm
橋本七海 氏 (慶応大)
Equivalence of categories of KK-theory or E-theory for $C^*$-algebras over topological spaces by reflection functors
[ 参考URL ]
https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm
トポロジー火曜セミナー
16:00-17:00 オンライン開催
セミナーのホームページから参加登録を行って下さい。
矢ヶ崎 達彦 氏 ( 京都工芸繊維大学)
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
セミナーのホームページから参加登録を行って下さい。
矢ヶ崎 達彦 氏 ( 京都工芸繊維大学)
Topological properties of groups of volume-preserving diffeomorphisms and groups of uniform homeomorphisms (JAPANESE)
[ 講演概要 ]
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.
[ 参考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年07月13日(月)
複素解析幾何セミナー
10:30-12:00 数理科学研究科棟(駒場) 126号室
神田 秀峰 氏 (東京大学)
Holomorphic polynomial crystallographic actions of nilpotent groups (Japanese)
https://forms.gle/8ERsVDLuKHwbVzm57
神田 秀峰 氏 (東京大学)
Holomorphic polynomial crystallographic actions of nilpotent groups (Japanese)
[ 講演概要 ]
It is a natural and still open question whether every simply connected nilpotent Lie group endowed with a left-invariant complex structure is biholomorphic to $\mathbb{C}^n$. In this talk, we give an affirmative answer under the additional assumption that the complex structure is nilpotent. Moreover, we construct such a biholomorphism explicitly by polynomial maps in exponential coordinates. As a consequence, every lattice in such a Lie group admits a free, properly discontinuous and cocompact action on $\mathbb{C}^n$ by holomorphic polynomial automorphisms. We interpret this as a holomorphic analogue of polynomial crystallographic actions, namely actions on $\mathbb{R}^n$ by polynomial diffeomorphisms that are free, properly discontinuous and cocompact, as introduced by Dekimpe, Igodt, and Lee.
[ 参考URL ]It is a natural and still open question whether every simply connected nilpotent Lie group endowed with a left-invariant complex structure is biholomorphic to $\mathbb{C}^n$. In this talk, we give an affirmative answer under the additional assumption that the complex structure is nilpotent. Moreover, we construct such a biholomorphism explicitly by polynomial maps in exponential coordinates. As a consequence, every lattice in such a Lie group admits a free, properly discontinuous and cocompact action on $\mathbb{C}^n$ by holomorphic polynomial automorphisms. We interpret this as a holomorphic analogue of polynomial crystallographic actions, namely actions on $\mathbb{R}^n$ by polynomial diffeomorphisms that are free, properly discontinuous and cocompact, as introduced by Dekimpe, Igodt, and Lee.
https://forms.gle/8ERsVDLuKHwbVzm57
2026年07月14日(火)
作用素環セミナー
16:45-18:15 数理科学研究科棟(駒場) 126号室
安藤浩志 氏 (千葉大学)
未定
[ 参考URL ]
https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm
安藤浩志 氏 (千葉大学)
未定
[ 参考URL ]
https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm
Lie群論・表現論セミナー
16:00-17:30 数理科学研究科棟(駒場) 056号室
トポロジー火曜セミナーと合同開催。
田中雄一郎 氏 (東大数理)
Visible actions of real reductive groups on complex algebraic varieties
トポロジー火曜セミナーと合同開催。
田中雄一郎 氏 (東大数理)
Visible actions of real reductive groups on complex algebraic varieties
[ 講演概要 ]
A unitary representation of a locally compact group is multiplicity-free if each irreducible representation appears at most once in its irreducible decomposition.
To provide a unified perspective on this property in the context of Lie group representations, T. Kobayashi introduced the theory of visible action for holomorphic actions of Lie groups on complex manifolds.
This approach enables us to understand many known examples uniformly and also leads to the discovery of new ones by utilizing Kobayashi’s propagation theorem of multiplicity-freeness property for visible actions.
In this talk, we will begin with the definition of visible action, illustrated with examples, and then explore some known results on classifications of visible actions and relationships among the coisotropicity, the sphericity and the visibility for group-actions on complex smooth algebraic varieties.
We will also discuss recent results based on unitary tricks for transferring properties of compact group-actions on complex flag manifolds to non-compact ones.
A unitary representation of a locally compact group is multiplicity-free if each irreducible representation appears at most once in its irreducible decomposition.
To provide a unified perspective on this property in the context of Lie group representations, T. Kobayashi introduced the theory of visible action for holomorphic actions of Lie groups on complex manifolds.
This approach enables us to understand many known examples uniformly and also leads to the discovery of new ones by utilizing Kobayashi’s propagation theorem of multiplicity-freeness property for visible actions.
In this talk, we will begin with the definition of visible action, illustrated with examples, and then explore some known results on classifications of visible actions and relationships among the coisotropicity, the sphericity and the visibility for group-actions on complex smooth algebraic varieties.
We will also discuss recent results based on unitary tricks for transferring properties of compact group-actions on complex flag manifolds to non-compact ones.
トポロジー火曜セミナー
16:00-17:30 数理科学研究科棟(駒場) hybrid/056号室
Lie群論・表現論セミナーと合同開催。 参加を希望される場合は、セミナーのウェブページをご覧下さい。
田中 雄一郎 氏 (東京大学大学院数理科学研究科)
Visible actions of real reductive groups on complex algebraic varieties (JAPANESE)
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html
Lie群論・表現論セミナーと合同開催。 参加を希望される場合は、セミナーのウェブページをご覧下さい。
田中 雄一郎 氏 (東京大学大学院数理科学研究科)
Visible actions of real reductive groups on complex algebraic varieties (JAPANESE)
[ 講演概要 ]
A unitary representation of a locally compact group is multiplicity-free if each irreducible representation appears at most once in its irreducible decomposition. To provide a unified perspective on this property in the context of Lie group representations, T. Kobayashi introduced the theory of visible action for holomorphic actions of Lie groups on complex manifolds. This approach enables us to understand many known examples uniformly and also leads to the discovery of new ones by utilizing Kobayashi's propagation theorem of multiplicity-freeness property for visible actions. In this talk, we will begin with the definition of visible action, illustrated with examples, and then explore some known results on classifications of visible actions and relationships among the coisotropicity, the sphericity and the visibility for group-actions on complex smooth algebraic varieties. We will also discuss recent results based on unitary tricks for transferring properties of compact group-actions on complex flag manifolds to non-compact ones.
[ 参考URL ]A unitary representation of a locally compact group is multiplicity-free if each irreducible representation appears at most once in its irreducible decomposition. To provide a unified perspective on this property in the context of Lie group representations, T. Kobayashi introduced the theory of visible action for holomorphic actions of Lie groups on complex manifolds. This approach enables us to understand many known examples uniformly and also leads to the discovery of new ones by utilizing Kobayashi's propagation theorem of multiplicity-freeness property for visible actions. In this talk, we will begin with the definition of visible action, illustrated with examples, and then explore some known results on classifications of visible actions and relationships among the coisotropicity, the sphericity and the visibility for group-actions on complex smooth algebraic varieties. We will also discuss recent results based on unitary tricks for transferring properties of compact group-actions on complex flag manifolds to non-compact ones.
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html
数値解析セミナー
16:30-18:00 数理科学研究科棟(駒場) 002号室
榊原航也 氏 (金沢大学理工研究域)
制約付き平面閉曲線流に対する安定化 dual-SAV パラメトリック有限要素法 (Japanese)
https://sites.google.com/g.ecc.u-tokyo.ac.jp/utnas-bulletin-board/
榊原航也 氏 (金沢大学理工研究域)
制約付き平面閉曲線流に対する安定化 dual-SAV パラメトリック有限要素法 (Japanese)
[ 講演概要 ]
曲率に駆動される平面閉曲線の時間発展をパラメトリック有限要素法で計算する際には，高階の幾何学的剛性に加え，節点の集中・疎化によるメッシュの劣化，さらに面積や酋長などの大域的制約に由来する非線型性を同時に扱う必要がある．本講演では，物理的な幾何エネルギーと人工的なメッシュ正則化エネルギーに対して，独立な2つの scalar auxiliary variable (SAV) を導入する安定化 dual-SAV パラメトリック有限要素法を紹介する．メッシュ正則化に対応する力を接線方向にのみ作用させることで，曲線の法線方向の幾何学的運動を変えることなく，節点の再配置を実現する．また，既知時刻の計量を凍結した半陰的離散化と，速度そのものに作用する零次安定化を組み合わせることにより，各時間ステップに現れる空間方向の問題を正定値対称な線型応答問題へと帰着させ，幾何 SAV エネルギーおよびメッシュ修正 SAV エネルギーに対する離散散逸則を導く．さらに，K 個の大域的制約を課す場合，ブロック消去によって残る非線型問題が，メッシュ節点数によらない K+1 次元の代数系に縮約されることを示す．曲線短縮流，面積保存曲線短縮流，曲線拡散流，ならびに面積・周長制約付き Helfrich 型流の数値例を通じて，時間精度，修正エネルギー散逸，制約を高精度に満たすこと，メッシュ品質および計算効率を検証する．
[ 参考URL ]曲率に駆動される平面閉曲線の時間発展をパラメトリック有限要素法で計算する際には，高階の幾何学的剛性に加え，節点の集中・疎化によるメッシュの劣化，さらに面積や酋長などの大域的制約に由来する非線型性を同時に扱う必要がある．本講演では，物理的な幾何エネルギーと人工的なメッシュ正則化エネルギーに対して，独立な2つの scalar auxiliary variable (SAV) を導入する安定化 dual-SAV パラメトリック有限要素法を紹介する．メッシュ正則化に対応する力を接線方向にのみ作用させることで，曲線の法線方向の幾何学的運動を変えることなく，節点の再配置を実現する．また，既知時刻の計量を凍結した半陰的離散化と，速度そのものに作用する零次安定化を組み合わせることにより，各時間ステップに現れる空間方向の問題を正定値対称な線型応答問題へと帰着させ，幾何 SAV エネルギーおよびメッシュ修正 SAV エネルギーに対する離散散逸則を導く．さらに，K 個の大域的制約を課す場合，ブロック消去によって残る非線型問題が，メッシュ節点数によらない K+1 次元の代数系に縮約されることを示す．曲線短縮流，面積保存曲線短縮流，曲線拡散流，ならびに面積・周長制約付き Helfrich 型流の数値例を通じて，時間精度，修正エネルギー散逸，制約を高精度に満たすこと，メッシュ品質および計算効率を検証する．
https://sites.google.com/g.ecc.u-tokyo.ac.jp/utnas-bulletin-board/
2026年07月17日(金)
談話会・数理科学講演会
15:30-16:30 数理科学研究科棟(駒場) NISSAY Lecture Hall号室
松井宏樹 氏 (東京大学大学院数理科学研究科)
力学系から生じる位相充足群およびC*環について (日本語)
松井宏樹 氏 (東京大学大学院数理科学研究科)
力学系から生じる位相充足群およびC*環について (日本語)
[ 講演概要 ]
カントール集合上の極小な力学系から位相充足群と呼ばれる可算無限群を構成することができる。この群はその交換子群が単純になるという著しい性質を持ち、さまざまな力学系から興味深い性質を持つ無限群を与えることができる。1992年にSteinによって導入されたStein群を一つの題材として、最近の研究の進展を概観・紹介したい。時間が許す範囲で、力学系から構成されるC*環やそのK群、或いは力学系自身のホモロジー群との関連についても触れたい。
カントール集合上の極小な力学系から位相充足群と呼ばれる可算無限群を構成することができる。この群はその交換子群が単純になるという著しい性質を持ち、さまざまな力学系から興味深い性質を持つ無限群を与えることができる。1992年にSteinによって導入されたStein群を一つの題材として、最近の研究の進展を概観・紹介したい。時間が許す範囲で、力学系から構成されるC*環やそのK群、或いは力学系自身のホモロジー群との関連についても触れたい。
2026年07月21日(火)
作用素環セミナー
16:45-18:15 数理科学研究科棟(駒場) 126号室
磯野優介 氏 (京大数理研)
Introduction to Tomita--Takesaki theory
[ 参考URL ]
https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm
磯野優介 氏 (京大数理研)
Introduction to Tomita--Takesaki theory
[ 参考URL ]
https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm
