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トポロジー火曜セミナー
過去の記録 ～05/02｜次回の予定｜今後の予定 05/03～
| 開催情報 | 火曜日 16:00～17:30 数理科学研究科棟(駒場) 056号室 |
|---|---|
| 担当者 | 池 祐一, 今野 北斗, 逆井卓也 |
| セミナーURL | https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index.html |
今後の予定
2026年05月12日(火)
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。
Sanghoon Kwak 氏 (Seoul National University)
Mapping class group of Infinite graph: 'Big' Out(Fn) (ENGLISH)
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。
Sanghoon Kwak 氏 (Seoul National University)
Mapping class group of Infinite graph: 'Big' Out(Fn) (ENGLISH)
[ 講演概要 ]
Algom-Kfir and Bestvina introduced the mapping class groups of locally finite, infinite graphs in 2021. Since Out(Fn) can be realized as the mapping group of a finite graph, their construction may be viewed as a "big" version of Out(Fn). In this talk, we survey the algebraic and coarse geometric properties of these groups and discuss a relationship with mapping class groups of infinite-type surfaces ("big mapping class groups"). This talk is based on joint work with Ryan Dickmann, George Domat, and Hannah Hoganson, in various collaborations.
[ 参考URL ]Algom-Kfir and Bestvina introduced the mapping class groups of locally finite, infinite graphs in 2021. Since Out(Fn) can be realized as the mapping group of a finite graph, their construction may be viewed as a "big" version of Out(Fn). In this talk, we survey the algebraic and coarse geometric properties of these groups and discuss a relationship with mapping class groups of infinite-type surfaces ("big mapping class groups"). This talk is based on joint work with Ryan Dickmann, George Domat, and Hannah Hoganson, in various collaborations.
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html
2026年05月19日(火)
17:30-18:30 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。
森田 陽介 氏 (九州大学)
Compact Clifford-Klein forms and homotopy theory of sphere bundles (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。
森田 陽介 氏 (九州大学)
Compact Clifford-Klein forms and homotopy theory of sphere bundles (JAPANESE)
[ 講演概要 ]
Let G/H be a homogeneous space of reductive type (such as the pseudo-Riemannian hyperbolic space H^{p,q}). If a discrete subgroup of G acts properly and freely on G/H, the quotient space becomes a manifold locally modelled on G/H and is called a Clifford-Klein form. In this talk, I will explain a new necessary condition on G/H for the existence of compact Clifford-Klein forms, formulated in terms of homotopy theory of sphere bundles. Our theorem and Adams's solution to the ‘vector fields on sphere’ problem (1962) together imply the following result: unless p is divisible by 2^{ν(q)}, there does not exist a compact complete pseudo-Riemannian manifolds of signature (p,q) with constant negative sectional curvature. Here, ν(q) is an explicit natural number roughly equal to q/2. This is joint work with Fanny Kassel and Nicolas Tholozan.
[ 参考URL ]Let G/H be a homogeneous space of reductive type (such as the pseudo-Riemannian hyperbolic space H^{p,q}). If a discrete subgroup of G acts properly and freely on G/H, the quotient space becomes a manifold locally modelled on G/H and is called a Clifford-Klein form. In this talk, I will explain a new necessary condition on G/H for the existence of compact Clifford-Klein forms, formulated in terms of homotopy theory of sphere bundles. Our theorem and Adams's solution to the ‘vector fields on sphere’ problem (1962) together imply the following result: unless p is divisible by 2^{ν(q)}, there does not exist a compact complete pseudo-Riemannian manifolds of signature (p,q) with constant negative sectional curvature. Here, ν(q) is an explicit natural number roughly equal to q/2. This is joint work with Fanny Kassel and Nicolas Tholozan.
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html
2026年05月26日(火)
16:00-17:30 数理科学研究科棟(駒場) hybrid/056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。
坂井 健人 氏 (東京大学大学院数理科学研究科)
On the large-scale geometry of k-multicurve graphs (JAPANESE)
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。
坂井 健人 氏 (東京大学大学院数理科学研究科)
On the large-scale geometry of k-multicurve graphs (JAPANESE)
[ 講演概要 ]
Graphs whose vertices are isotopy classes of simple closed curves, or multicurves, on surfaces have been widely studied, since they admit natural actions of mapping class groups. The curve graph and the pants graph are two fundamental examples. These graphs have found many applications in low-dimensional topology, including the study of Teichmüller spaces, Kleinian groups, and topology of 3-manifolds. In particular, the Gromov hyperbolicity of the curve graph, established by Masur and Minsky, played an important role in the proof of the Ending Lamination Theorem.
The k-multicurve graph, introduced by Erlandsson and Fanoni, is a graph whose vertices are multicurves with k components. It provides a natural interpolation between the curve graph and the pants graph. In this talk, we will present results on large-scale geometric properties of k-multicurve graphs, including hyperbolicity, relative hyperbolicity, and quasi-flat rank. If time permits, we will also discuss some connections with mapping class groups and Teichmüller spaces. This talk is based on joint work with Erika Kuno (Shibaura Institute of Technology) and Rin Kuramochi (The University of Tokyo).
[ 参考URL ]Graphs whose vertices are isotopy classes of simple closed curves, or multicurves, on surfaces have been widely studied, since they admit natural actions of mapping class groups. The curve graph and the pants graph are two fundamental examples. These graphs have found many applications in low-dimensional topology, including the study of Teichmüller spaces, Kleinian groups, and topology of 3-manifolds. In particular, the Gromov hyperbolicity of the curve graph, established by Masur and Minsky, played an important role in the proof of the Ending Lamination Theorem.
The k-multicurve graph, introduced by Erlandsson and Fanoni, is a graph whose vertices are multicurves with k components. It provides a natural interpolation between the curve graph and the pants graph. In this talk, we will present results on large-scale geometric properties of k-multicurve graphs, including hyperbolicity, relative hyperbolicity, and quasi-flat rank. If time permits, we will also discuss some connections with mapping class groups and Teichmüller spaces. This talk is based on joint work with Erika Kuno (Shibaura Institute of Technology) and Rin Kuramochi (The University of Tokyo).
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html
