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トポロジー火曜セミナー
過去の記録 ～04/24｜次回の予定｜今後の予定 04/25～
| 開催情報 | 火曜日 17:00～18:30 数理科学研究科棟(駒場) 056号室 |
|---|---|
| 担当者 | 河澄 響矢, 北山 貴裕, 逆井卓也 |
| セミナーURL | http://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index.html |
過去の記録
2015年04月07日(火)
17:00-18:30 数理科学研究科棟(駒場) 056号室
Tea : 16:30-17:00 Common Room
植田 一石 氏 (東京大学大学院数理科学研究科)
Potential functions for Grassmannians (JAPANESE)
Tea : 16:30-17:00 Common Room
植田 一石 氏 (東京大学大学院数理科学研究科)
Potential functions for Grassmannians (JAPANESE)
[ 講演概要 ]
Potential functions are Floer-theoretic invariants
obtained by counting Maslov index 2 disks
with Lagrangian boundary conditions.
In the talk, we will discuss our joint work
with Yanki Lekili and Yuichi Nohara
on Lagrangian torus fibrations on the Grassmannian
of 2-planes in an n-space,
the potential functions of their Lagrangian torus fibers,
and their relation with mirror symmetry for Grassmannians.
Potential functions are Floer-theoretic invariants
obtained by counting Maslov index 2 disks
with Lagrangian boundary conditions.
In the talk, we will discuss our joint work
with Yanki Lekili and Yuichi Nohara
on Lagrangian torus fibrations on the Grassmannian
of 2-planes in an n-space,
the potential functions of their Lagrangian torus fibers,
and their relation with mirror symmetry for Grassmannians.
2015年03月24日(火)
17:00-18:30 数理科学研究科棟(駒場) 056号室
Mina Aganagic 氏 (University of California, Berkeley)
Knots and Mirror Symmetry (ENGLISH)
Mina Aganagic 氏 (University of California, Berkeley)
Knots and Mirror Symmetry (ENGLISH)
[ 講演概要 ]
I will describe two conjectures relating knot theory and mirror symmetry. One can associate, to every knot K, one a Calabi-Yau manifold Y(K), which depends on the homotopy type of the knot only. The first conjecture is that Y(K) arises by a generalization of SYZ mirror symmetry, as mirror to the conifold, O(-1)+O(-1)->P^1. The second conjecture is that topological string provides a quantization of Y(K) which leads to quantum HOMFLY invariants of the knot. The conjectures are based on joint work with C. Vafa and also with T.Ekholm, L. Ng.
I will describe two conjectures relating knot theory and mirror symmetry. One can associate, to every knot K, one a Calabi-Yau manifold Y(K), which depends on the homotopy type of the knot only. The first conjecture is that Y(K) arises by a generalization of SYZ mirror symmetry, as mirror to the conifold, O(-1)+O(-1)->P^1. The second conjecture is that topological string provides a quantization of Y(K) which leads to quantum HOMFLY invariants of the knot. The conjectures are based on joint work with C. Vafa and also with T.Ekholm, L. Ng.
2015年03月10日(火)
16:30-18:00 数理科学研究科棟(駒場) 056号室
Tea: 16:00-16:30 Common Room ; This seminar will be held as FMSP Lectures.
Andrei Pajitnov 氏 (Univ. de Nantes)
Arnold conjecture, Floer homology,
and augmentation ideals of finite groups.
(ENGLISH)
Tea: 16:00-16:30 Common Room ; This seminar will be held as FMSP Lectures.
Andrei Pajitnov 氏 (Univ. de Nantes)
Arnold conjecture, Floer homology,
and augmentation ideals of finite groups.
(ENGLISH)
[ 講演概要 ]
Let H be a generic time-dependent 1-periodic
Hamiltonian on a closed weakly monotone
symplectic manifold M. We construct a refined version
of the Floer chain complex associated to (M,H),
and use it to obtain new lower bounds for the number P(H)
of the 1-periodic orbits of the corresponding hamiltonian
vector field. We prove in particular that
if the fundamental group of M is finite
and solvable or simple, then P(H)
is not less than the minimal number
of generators of the fundamental group.
This is joint work with Kaoru Ono.
Let H be a generic time-dependent 1-periodic
Hamiltonian on a closed weakly monotone
symplectic manifold M. We construct a refined version
of the Floer chain complex associated to (M,H),
and use it to obtain new lower bounds for the number P(H)
of the 1-periodic orbits of the corresponding hamiltonian
vector field. We prove in particular that
if the fundamental group of M is finite
and solvable or simple, then P(H)
is not less than the minimal number
of generators of the fundamental group.
This is joint work with Kaoru Ono.
2015年01月20日(火)
16:30-17:30 数理科学研究科棟(駒場) 056号室
Tea : 16:00-16:30 Common Room
吉安 徹 氏 (東京大学大学院数理科学研究科)
On Lagrangian caps and their applications (JAPANESE)
Tea : 16:00-16:30 Common Room
吉安 徹 氏 (東京大学大学院数理科学研究科)
On Lagrangian caps and their applications (JAPANESE)
[ 講演概要 ]
In 2013, Y. Eliashberg and E. Murphy established the $h$-principle for
exact Lagrangian embeddings with a concave Legendrian boundary. In this
talk, I will explain a modification of their $h$-principle and show
applications to Lagrangian submanifolds in the complex projective spaces.
In 2013, Y. Eliashberg and E. Murphy established the $h$-principle for
exact Lagrangian embeddings with a concave Legendrian boundary. In this
talk, I will explain a modification of their $h$-principle and show
applications to Lagrangian submanifolds in the complex projective spaces.
2015年01月13日(火)
16:30-18:00 数理科学研究科棟(駒場) 056号室
Tea : 16:00-16:30 Common Room
吉田 建一 氏 (東京大学大学院数理科学研究科)
Stable presentation length of 3-manifold groups (JAPANESE)
Tea : 16:00-16:30 Common Room
吉田 建一 氏 (東京大学大学院数理科学研究科)
Stable presentation length of 3-manifold groups (JAPANESE)
[ 講演概要 ]
We will introduce the stable presentation length
of a finitely presented group, which is defined
by stabilizing the presentation length for the
finite index subgroups. The stable presentation
length of the fundamental group of a 3-manifold
is an analogue of the simplicial volume and the
stable complexity introduced by Francaviglia,
Frigerio and Martelli. We will explain some
similarities of stable presentation length with
simplicial volume and stable complexity.
We will introduce the stable presentation length
of a finitely presented group, which is defined
by stabilizing the presentation length for the
finite index subgroups. The stable presentation
length of the fundamental group of a 3-manifold
is an analogue of the simplicial volume and the
stable complexity introduced by Francaviglia,
Frigerio and Martelli. We will explain some
similarities of stable presentation length with
simplicial volume and stable complexity.
2014年12月16日(火)
17:10-18:10 数理科学研究科棟(駒場) 056号室
Tea : 16:50-17:10 Common Room
岩瀬 則夫 氏 (九州大学)
Differential forms in diffeological spaces (JAPANESE)
Tea : 16:50-17:10 Common Room
岩瀬 則夫 氏 (九州大学)
Differential forms in diffeological spaces (JAPANESE)
[ 講演概要 ]
The idea of a space with smooth structure is first introduced by K. T. Chen in his study of a loop space to employ the idea of iterated path integrals.
Following the pattern established by Chen, J. M. Souriau introduced his version of a space with smooth structure which is now called diffeology and become one of the most exciting topics in Algebraic Topology. Following Souriau, P. I.-Zenmour presented de Rham theory associated to a diffeology of a space. However, if one tries to show a version of de Rham theorem for a general diffeological space, he must encounter a difficulty to show the existence of a partition of unity and thus the exactness of the Mayer-Vietoris sequence. To resolve such difficulties, we introduce a new definition of differential forms.
The idea of a space with smooth structure is first introduced by K. T. Chen in his study of a loop space to employ the idea of iterated path integrals.
Following the pattern established by Chen, J. M. Souriau introduced his version of a space with smooth structure which is now called diffeology and become one of the most exciting topics in Algebraic Topology. Following Souriau, P. I.-Zenmour presented de Rham theory associated to a diffeology of a space. However, if one tries to show a version of de Rham theorem for a general diffeological space, he must encounter a difficulty to show the existence of a partition of unity and thus the exactness of the Mayer-Vietoris sequence. To resolve such difficulties, we introduce a new definition of differential forms.
2014年12月09日(火)
16:30-18:00 数理科学研究科棟(駒場) 056号室
Tea : 16:00-16:30 Common Room
藤原 耕二 氏 (京都大学大学院理学研究科)
Stable commutator length on mapping class groups (JAPANESE)
Tea : 16:00-16:30 Common Room
藤原 耕二 氏 (京都大学大学院理学研究科)
Stable commutator length on mapping class groups (JAPANESE)
[ 講演概要 ]
Let MCG(S) be the mapping class group of a closed orientable surface S.
We give a precise condition (in terms of the Nielsen-Thurston
decomposition) when an element
in MCG(S) has positive stable commutator length.
Stable commutator length tends to be positive if there is "negative
curvature".
The proofs use our earlier construction in the paper "Constructing group
actions on quasi-trees and applications to mapping class groups" of
group actions on quasi-trees.
This is a joint work with Bestvina and Bromberg.
Let MCG(S) be the mapping class group of a closed orientable surface S.
We give a precise condition (in terms of the Nielsen-Thurston
decomposition) when an element
in MCG(S) has positive stable commutator length.
Stable commutator length tends to be positive if there is "negative
curvature".
The proofs use our earlier construction in the paper "Constructing group
actions on quasi-trees and applications to mapping class groups" of
group actions on quasi-trees.
This is a joint work with Bestvina and Bromberg.
2014年12月02日(火)
16:30-18:00 数理科学研究科棟(駒場) 056号室
Tea: 16:00-16:30 Common Room
窪田 陽介 氏 (東京大学大学院数理科学研究科)
The Atiyah-Segal completion theorem in noncommutative topology (JAPANESE)
Tea: 16:00-16:30 Common Room
窪田 陽介 氏 (東京大学大学院数理科学研究科)
The Atiyah-Segal completion theorem in noncommutative topology (JAPANESE)
[ 講演概要 ]
C*環の位相的な性質を扱う"非可換"トポロジーの理論を用
いて，Atiyah-Segal completion theoremに新しい視点を導入する．ここで，R.
MeyerとR. Nestらによって発展したKasparov categoryの三角圏としてのホモロ
ジー代数が中心的な役割を果たす．また，これは系として同変Kホモロジーや捩
れK理論に対するAtiyah-Segal型のcompletion theoremを含む．これは荒野悠輝
氏との共同研究である．
C*環の位相的な性質を扱う"非可換"トポロジーの理論を用
いて，Atiyah-Segal completion theoremに新しい視点を導入する．ここで，R.
MeyerとR. Nestらによって発展したKasparov categoryの三角圏としてのホモロ
ジー代数が中心的な役割を果たす．また，これは系として同変Kホモロジーや捩
れK理論に対するAtiyah-Segal型のcompletion theoremを含む．これは荒野悠輝
氏との共同研究である．
2014年11月25日(火)
16:30-18:00 数理科学研究科棟(駒場) 056号室
Tea: 16:00-16:30 Common Room
齋藤 昌彦 氏 (University of South Florida)
Quandle knot invariants and applications (JAPANESE)
Tea: 16:00-16:30 Common Room
齋藤 昌彦 氏 (University of South Florida)
Quandle knot invariants and applications (JAPANESE)
[ 講演概要 ]
A quandles is an algebraic structure closely related to knots. Homology theories of
quandles have been defined, and their cocycles are used to construct invariants for
classical knots, spatial graphs and knotted surfaces. In this talk, an overview is given
for quandle cocycle invariants and their applications to geometric properties of knots.
The current status of computations, recent developments and open problems will also
be discussed.
A quandles is an algebraic structure closely related to knots. Homology theories of
quandles have been defined, and their cocycles are used to construct invariants for
classical knots, spatial graphs and knotted surfaces. In this talk, an overview is given
for quandle cocycle invariants and their applications to geometric properties of knots.
The current status of computations, recent developments and open problems will also
be discussed.
2014年11月18日(火)
16:30-18:00 数理科学研究科棟(駒場) 056号室
Tea: 16:00 - 16:30 Common Room
Charles Siegel 氏 (Kavli IPMU)
A Modular Operad of Embedded Curves (ENGLISH)
Tea: 16:00 - 16:30 Common Room
Charles Siegel 氏 (Kavli IPMU)
A Modular Operad of Embedded Curves (ENGLISH)
[ 講演概要 ]
Modular operads were introduced by Getzler and Kapranov to formalize the structure of gluing maps between moduli of stable marked curves. We present a construction of analogous gluing maps between moduli of pluri-log-canonically embedded marked curves, which fit together to give a modular operad of embedded curves. This is joint work with Satoshi Kondo and Jesse Wolfson.
Modular operads were introduced by Getzler and Kapranov to formalize the structure of gluing maps between moduli of stable marked curves. We present a construction of analogous gluing maps between moduli of pluri-log-canonically embedded marked curves, which fit together to give a modular operad of embedded curves. This is joint work with Satoshi Kondo and Jesse Wolfson.
2014年11月11日(火)
16:30-18:00 数理科学研究科棟(駒場) 056号室
Tea: 16:00 - 16:30 Common Room
Kenneth Baker 氏 (University of Miami)
Unifying unexpected exceptional Dehn surgeries (ENGLISH)
Tea: 16:00 - 16:30 Common Room
Kenneth Baker 氏 (University of Miami)
Unifying unexpected exceptional Dehn surgeries (ENGLISH)
[ 講演概要 ]
This past summer Dunfield-Hoffman-Licata produced examples of asymmetric, hyperbolic, 1-cusped 3-manifolds with pairs of lens space Dehn fillings through a search of the extended SnapPea census.
Examinations of these examples with Hoffman and Licata lead us to coincidences with other work in progress that gives a simple holistic topological approach towards producing and extending many of these families. In this talk we'll explicitly describe our construction and discuss related applications of the technique.
This past summer Dunfield-Hoffman-Licata produced examples of asymmetric, hyperbolic, 1-cusped 3-manifolds with pairs of lens space Dehn fillings through a search of the extended SnapPea census.
Examinations of these examples with Hoffman and Licata lead us to coincidences with other work in progress that gives a simple holistic topological approach towards producing and extending many of these families. In this talk we'll explicitly describe our construction and discuss related applications of the technique.
2014年11月04日(火)
16:30-18:00 数理科学研究科棟(駒場) 056号室
Tea : 16:00-16:30 Common Room
Brian Bowditch 氏 (University of Warwick)
The coarse geometry of Teichmuller space. (ENGLISH)
Tea : 16:00-16:30 Common Room
Brian Bowditch 氏 (University of Warwick)
The coarse geometry of Teichmuller space. (ENGLISH)
[ 講演概要 ]
We describe some results regarding the coarse geometry of the
Teichmuller space
of a compact surface. In particular, we describe when the Teichmuller
space admits quasi-isometric embeddings of euclidean spaces and
half-spaces.
We also give some partial results regarding the quasi-isometric rigidity
of Teichmuller space. These results are based on the fact that Teichmuller
space admits a ternary operation, natural up to bounded distance
which endows it with the structure of a coarse median space.
We describe some results regarding the coarse geometry of the
Teichmuller space
of a compact surface. In particular, we describe when the Teichmuller
space admits quasi-isometric embeddings of euclidean spaces and
half-spaces.
We also give some partial results regarding the quasi-isometric rigidity
of Teichmuller space. These results are based on the fact that Teichmuller
space admits a ternary operation, natural up to bounded distance
which endows it with the structure of a coarse median space.
2014年10月21日(火)
16:30-18:00 数理科学研究科棟(駒場) 056号室
Tea: 16:00 - 16:30 コモンルーム
秋田 利之 氏 (北海道大学)
Vanishing theorems for p-local homology of Coxeter groups and their alternating subgroups (JAPANESE)
Tea: 16:00 - 16:30 コモンルーム
秋田 利之 氏 (北海道大学)
Vanishing theorems for p-local homology of Coxeter groups and their alternating subgroups (JAPANESE)
[ 講演概要 ]
Given a prime number $p$, we estimate vanishing ranges of $p$-local homology groups of Coxeter groups (of possibly infinite order) and alternating subgroups of finite reflection groups. Our results generalize those by Nakaoka for symmetric groups and Kleshchev-Nakano and Burichenko for alternating groups. The key ingredient is the equivariant homology of Coxeter complexes.
Given a prime number $p$, we estimate vanishing ranges of $p$-local homology groups of Coxeter groups (of possibly infinite order) and alternating subgroups of finite reflection groups. Our results generalize those by Nakaoka for symmetric groups and Kleshchev-Nakano and Burichenko for alternating groups. The key ingredient is the equivariant homology of Coxeter complexes.
2014年10月07日(火)
16:30-18:00 数理科学研究科棟(駒場) 056号室
Tea: 16:00 - 16:30 コモンルーム
入江 慶 氏 (京都大学数理解析研究所)
Transversality problems in string topology and de Rham chains (JAPANESE)
Tea: 16:00 - 16:30 コモンルーム
入江 慶 氏 (京都大学数理解析研究所)
Transversality problems in string topology and de Rham chains (JAPANESE)
[ 講演概要 ]
ストリング・トポロジーの出発点は,多様体の自由ループ空間のホモロジーの上にBatalin-Vilkovisky(BV)代数の構造を発見したChas-Sullivanの仕事である.
この結果を精密化して鎖レベルの構造を定義することは重要な問題であるが,まだ決定版の解答は得られていない.困難の一つは,交叉積を鎖レベルで定義する際に現れる,横断正則性の問題である.
講演では,de Rham 鎖というものを用いることでこの困難を回避し,鎖レベルの構造が部分的に実現できるということを説明したい.
ストリング・トポロジーの出発点は,多様体の自由ループ空間のホモロジーの上にBatalin-Vilkovisky(BV)代数の構造を発見したChas-Sullivanの仕事である.
この結果を精密化して鎖レベルの構造を定義することは重要な問題であるが,まだ決定版の解答は得られていない.困難の一つは,交叉積を鎖レベルで定義する際に現れる,横断正則性の問題である.
講演では,de Rham 鎖というものを用いることでこの困難を回避し,鎖レベルの構造が部分的に実現できるということを説明したい.
2014年07月22日(火)
16:30-18:00 数理科学研究科棟(駒場) 056号室
Tea: 16:00 - 16:30 コモンルーム
Jesse Wolfson 氏 (Northwestern University)
The Index Map and Reciprocity Laws for Contou-Carrere Symbols (ENGLISH)
Tea: 16:00 - 16:30 コモンルーム
Jesse Wolfson 氏 (Northwestern University)
The Index Map and Reciprocity Laws for Contou-Carrere Symbols (ENGLISH)
[ 講演概要 ]
In the 1960s, Atiyah and Janich constructed the families index as a natural map from the space of Fredholm operators to the classifying space of topological K-theory, and showed it to be an equivalence. In joint work with Oliver Braunling and Michael Groechenig, we construct an analogous index map in algebraic K-theory. Building on recent work of Sho Saito, we show this provides an analogue of Atiyah and Janich's equivalence. More significantly, the index map allows us to relate the Contou-Carrere symbol, a local analytic invariant of schemes, to algebraic K-theory. Using this, we provide new proofs of reciprocity laws for Contou-Carrere symbols in dimension 1 (first established by Anderson--Pablos Romo) and 2 (established recently by Osipov--Zhu). We extend these reciprocity laws to all dimensions.
In the 1960s, Atiyah and Janich constructed the families index as a natural map from the space of Fredholm operators to the classifying space of topological K-theory, and showed it to be an equivalence. In joint work with Oliver Braunling and Michael Groechenig, we construct an analogous index map in algebraic K-theory. Building on recent work of Sho Saito, we show this provides an analogue of Atiyah and Janich's equivalence. More significantly, the index map allows us to relate the Contou-Carrere symbol, a local analytic invariant of schemes, to algebraic K-theory. Using this, we provide new proofs of reciprocity laws for Contou-Carrere symbols in dimension 1 (first established by Anderson--Pablos Romo) and 2 (established recently by Osipov--Zhu). We extend these reciprocity laws to all dimensions.
2014年07月08日(火)
16:30-18:00 数理科学研究科棟(駒場) 056号室
Tea: 16:00 - 16:30 コモンルーム
Ingrid Irmer 氏 (JSPS, 東京大学大学院数理科学研究科)
The Johnson homomorphism and a family of curve graphs (ENGLISH)
Tea: 16:00 - 16:30 コモンルーム
Ingrid Irmer 氏 (JSPS, 東京大学大学院数理科学研究科)
The Johnson homomorphism and a family of curve graphs (ENGLISH)
[ 講演概要 ]
Abstract: A family of curve graphs of an oriented surface $S_{g,1}$ will be defined on which there exists a natural orientation, coming from the orientation of subsurfaces. Distances in these graphs represent commutator lengths in $\\pi_{1}(S_{g,1})$. The displacement of vertices in the graphs under the action of the Torelli group is used to give a combinatorial description of the Johnson homomorphism."
Abstract: A family of curve graphs of an oriented surface $S_{g,1}$ will be defined on which there exists a natural orientation, coming from the orientation of subsurfaces. Distances in these graphs represent commutator lengths in $\\pi_{1}(S_{g,1})$. The displacement of vertices in the graphs under the action of the Torelli group is used to give a combinatorial description of the Johnson homomorphism."
2014年07月01日(火)
16:30-18:00 数理科学研究科棟(駒場) 056号室
Tea: 16:00 - 16:30 コモンルーム
今城 洋亮 氏 (Kavli IPMU)
Singularities of special Lagrangian submanifolds (JAPANESE)
Tea: 16:00 - 16:30 コモンルーム
今城 洋亮 氏 (Kavli IPMU)
Singularities of special Lagrangian submanifolds (JAPANESE)
[ 講演概要 ]
There are interesting invariants defined by "counting" geometric
objects, such as instantons in dimension 4 and pseudo-holomorphic curves
in symplectic manifolds. To do the counting in a sensible way, however,
we have to care about singularities of the geometric objects. Special
Lagrangian submanifolds seem very difficult to "count" as their
singularities may be very complicated. I'll talk about simple
singularities for which we can make an analogy with instantons in
dimension 4 and pseudo-holomorphic curves in symplectic manifolds. To do
it I'll use some techniques from geometric measure theory and Lagrangian
Floer theory, and the Floer-theoretic part is a joint work with Dominic
Joyce and Oliveira dos Santos.
There are interesting invariants defined by "counting" geometric
objects, such as instantons in dimension 4 and pseudo-holomorphic curves
in symplectic manifolds. To do the counting in a sensible way, however,
we have to care about singularities of the geometric objects. Special
Lagrangian submanifolds seem very difficult to "count" as their
singularities may be very complicated. I'll talk about simple
singularities for which we can make an analogy with instantons in
dimension 4 and pseudo-holomorphic curves in symplectic manifolds. To do
it I'll use some techniques from geometric measure theory and Lagrangian
Floer theory, and the Floer-theoretic part is a joint work with Dominic
Joyce and Oliveira dos Santos.
2014年06月24日(火)
17:10-18:10 数理科学研究科棟(駒場) 056号室
Tea: 16:50 - 17:10 コモンルーム
野坂 武史 氏 (九州大学数理学研究院)
On third homologies of quandles and of groups via Inoue-Kabaya map (JAPANESE)
Tea: 16:50 - 17:10 コモンルーム
野坂 武史 氏 (九州大学数理学研究院)
On third homologies of quandles and of groups via Inoue-Kabaya map (JAPANESE)
[ 講演概要 ]
In this talk, we demonstrate certain quandles, which are defined from a
group $G$ and an isomorphism $¥rho:G - G$, and introduce the following
results: First, "Inoue-Kabaya chain map" is formulated as a map from
quandle homology to group homology. For example, with respect to every
Alexander quandle over F_q, the all of Mochizuki 3-cocycle is derived
from some group 3-cocycle, and mostly interpreted by a Massey products.
In addition, for universal centrally extended quandles, the chain map
induces an isomorphism between the 3-rd homologies (up to certain
torsion parts).
In this talk, we demonstrate certain quandles, which are defined from a
group $G$ and an isomorphism $¥rho:G - G$, and introduce the following
results: First, "Inoue-Kabaya chain map" is formulated as a map from
quandle homology to group homology. For example, with respect to every
Alexander quandle over F_q, the all of Mochizuki 3-cocycle is derived
from some group 3-cocycle, and mostly interpreted by a Massey products.
In addition, for universal centrally extended quandles, the chain map
induces an isomorphism between the 3-rd homologies (up to certain
torsion parts).
2014年06月17日(火)
16:30-18:00 数理科学研究科棟(駒場) 002号室
Tea: 16:00 - 16:30 コモンルーム
松田 能文 氏 (青山学院大学)
2次元軌道体群の円周への作用の有界オイラー数 (JAPANESE)
Tea: 16:00 - 16:30 コモンルーム
松田 能文 氏 (青山学院大学)
2次元軌道体群の円周への作用の有界オイラー数 (JAPANESE)
[ 講演概要 ]
Burger,Iozzi,Wienhardは連結かつ向き付けられた有限型の穴あき曲面の基本群
の円周への作用に対して有界オイラー数を定義した.有界オイラー数を含むMilnor-Wood型
の不等式が成立しその最大性はフックス作用を準共役を除いて特徴付ける.被覆を考えること
により有界オイラー数の定義は2次元軌道体群の作用に対して拡張される.Milnor-Wood型の
不等式およびフックス作用の特徴付けはこの場合にも成立する.この講演では,モジュラー群
などのいくつかの2次元軌道体群のフックス作用の持ち上げがいつ有界オイラー数により特徴
づけられるかについて記述する.
Burger,Iozzi,Wienhardは連結かつ向き付けられた有限型の穴あき曲面の基本群
の円周への作用に対して有界オイラー数を定義した.有界オイラー数を含むMilnor-Wood型
の不等式が成立しその最大性はフックス作用を準共役を除いて特徴付ける.被覆を考えること
により有界オイラー数の定義は2次元軌道体群の作用に対して拡張される.Milnor-Wood型の
不等式およびフックス作用の特徴付けはこの場合にも成立する.この講演では,モジュラー群
などのいくつかの2次元軌道体群のフックス作用の持ち上げがいつ有界オイラー数により特徴
づけられるかについて記述する.
2014年06月10日(火)
16:30-18:00 数理科学研究科棟(駒場) 056号室
Tea: 16:00 - 16:30 コモンルーム
小鳥居 祐香 氏 (東京大学大学院数理科学研究科)
On relation between the Milnor's $¥mu$-invariant and HOMFLYPT
polynomial (JAPANESE)
Tea: 16:00 - 16:30 コモンルーム
小鳥居 祐香 氏 (東京大学大学院数理科学研究科)
On relation between the Milnor's $¥mu$-invariant and HOMFLYPT
polynomial (JAPANESE)
[ 講演概要 ]
Milnor introduced a family of invariants for ordered oriented link,
called $¥bar{¥mu}$-invariants. Polyak showed a relation between the $¥
bar{¥mu}$-invariant of length 3 sequence and Conway polynomial.
Moreover, Habegger-Lin showed that Milnor's invariants are invariants of
string link, called $¥mu$-invariants. We show that any $¥mu$-invariant
of length $¥leq k$ can be represented as a combination of HOMFLYPT
polynomials if all $¥mu$-invariant of length $¥leq k-2$ vanish.
This result is an extension of Polyak's result.
Milnor introduced a family of invariants for ordered oriented link,
called $¥bar{¥mu}$-invariants. Polyak showed a relation between the $¥
bar{¥mu}$-invariant of length 3 sequence and Conway polynomial.
Moreover, Habegger-Lin showed that Milnor's invariants are invariants of
string link, called $¥mu$-invariants. We show that any $¥mu$-invariant
of length $¥leq k$ can be represented as a combination of HOMFLYPT
polynomials if all $¥mu$-invariant of length $¥leq k-2$ vanish.
This result is an extension of Polyak's result.
2014年06月03日(火)
16:30-18:00 数理科学研究科棟(駒場) 056号室
Tea: 16:00 - 16:30 コモンルーム
高倉 樹 氏 (中央大学・理工学部)
Vector partition functions and the topology of multiple weight varieties
(JAPANESE)
Tea: 16:00 - 16:30 コモンルーム
高倉 樹 氏 (中央大学・理工学部)
Vector partition functions and the topology of multiple weight varieties
(JAPANESE)
[ 講演概要 ]
A multiple weight variety is a symplectic quotient of a direct product
of several coadjoint orbits of a compact Lie group $G$, with respect to
the diagonal action of the maximal torus. Its geometry and topology are
closely related to the combinatorics concerned with the weight space
decomposition of a tensor product of irreducible representations of $G$.
For example, when considering the Riemann-Roch index, we are naturally
lead to the study of vector partition functions with multiplicities.
In this talk, we discuss some formulas for vector partition functions,
especially a generalization of the formula of Brion-Vergne. Then, by
using
them, we investigate the structure of the cohomology of certain multiple
weight varieties of type $A$ in detail.
A multiple weight variety is a symplectic quotient of a direct product
of several coadjoint orbits of a compact Lie group $G$, with respect to
the diagonal action of the maximal torus. Its geometry and topology are
closely related to the combinatorics concerned with the weight space
decomposition of a tensor product of irreducible representations of $G$.
For example, when considering the Riemann-Roch index, we are naturally
lead to the study of vector partition functions with multiplicities.
In this talk, we discuss some formulas for vector partition functions,
especially a generalization of the formula of Brion-Vergne. Then, by
using
them, we investigate the structure of the cohomology of certain multiple
weight varieties of type $A$ in detail.
2014年05月27日(火)
16:30-18:00 数理科学研究科棟(駒場) 056号室
Tea: 16:00 - 16:30 コモンルーム
藤川 英華 氏 (千葉大学大学院理学研究科)
The Teichmuller space and the stable quasiconformal mapping class group for a Riemann surface of infinite type (JAPANESE)
Tea: 16:00 - 16:30 コモンルーム
藤川 英華 氏 (千葉大学大学院理学研究科)
The Teichmuller space and the stable quasiconformal mapping class group for a Riemann surface of infinite type (JAPANESE)
[ 講演概要 ]
We explain recent developments of the theory of infinite dimensional Teichmuller space. In particular, we observe the dynamics of the orbits by the action of the stable quasiconformal mapping class group on the Teichmuller space and consider the relationship with the asymptotic Teichmuller space. We also introduce the generalized fixed point theorem and the Nielsen realization theorem. Furthermore, we investigate the moduli space of Riemann surface of infinite type.
We explain recent developments of the theory of infinite dimensional Teichmuller space. In particular, we observe the dynamics of the orbits by the action of the stable quasiconformal mapping class group on the Teichmuller space and consider the relationship with the asymptotic Teichmuller space. We also introduce the generalized fixed point theorem and the Nielsen realization theorem. Furthermore, we investigate the moduli space of Riemann surface of infinite type.
2014年05月20日(火)
16:30-18:00 数理科学研究科棟(駒場) 056号室
Tea: 16:00 - 16:30 コモンルーム
黒木 慎太郎 氏 (東京大学大学院数理科学研究科)
An application of torus graphs to characterize torus manifolds
with extended actions (JAPANESE)
Tea: 16:00 - 16:30 コモンルーム
黒木 慎太郎 氏 (東京大学大学院数理科学研究科)
An application of torus graphs to characterize torus manifolds
with extended actions (JAPANESE)
[ 講演概要 ]
A torus manifold is a compact, oriented 2n-dimensional T^n-
manifolds with fixed points. This notion is introduced by Hattori and
Masuda as a topological generalization of toric manifolds. For a given
torus manifold, we can define a labelled graph called a torus graph (
this may be regarded as a generalization of some class of GKM graphs).
It is known that the equivariant cohomology ring of some nice class of
torus manifolds can be computed by using a combinatorial data of torus
graphs. In this talk, we study which torus action of torus manifolds can
be extended to a non-abelian compact connected Lie group. To do this, we
introduce root systems of (abstract) torus graphs and characterize
extended actions of torus manifolds. This is a joint work with Mikiya
Masuda.
A torus manifold is a compact, oriented 2n-dimensional T^n-
manifolds with fixed points. This notion is introduced by Hattori and
Masuda as a topological generalization of toric manifolds. For a given
torus manifold, we can define a labelled graph called a torus graph (
this may be regarded as a generalization of some class of GKM graphs).
It is known that the equivariant cohomology ring of some nice class of
torus manifolds can be computed by using a combinatorial data of torus
graphs. In this talk, we study which torus action of torus manifolds can
be extended to a non-abelian compact connected Lie group. To do this, we
introduce root systems of (abstract) torus graphs and characterize
extended actions of torus manifolds. This is a joint work with Mikiya
Masuda.
2014年05月13日(火)
16:30-18:00 数理科学研究科棟(駒場) 056号室
Tea: 16:00 - 16:30 コモンルーム
足助 太郎 氏 (東京大学大学院数理科学研究科)
Transverse projective structures of foliations and deformations of the Godbillon-Vey class (JAPANESE)
Tea: 16:00 - 16:30 コモンルーム
足助 太郎 氏 (東京大学大学院数理科学研究科)
Transverse projective structures of foliations and deformations of the Godbillon-Vey class (JAPANESE)
[ 講演概要 ]
Given a smooth family of foliations, we can define the derivative of the Godbillon-Vey class
with respect to the family. The derivative is known to be represented in terms of the projective
Schwarzians of holonomy maps. In this talk, we will study transverse projective structures
and connections, and show that the derivative is in fact determined by the projective structure
and the family.
Given a smooth family of foliations, we can define the derivative of the Godbillon-Vey class
with respect to the family. The derivative is known to be represented in terms of the projective
Schwarzians of holonomy maps. In this talk, we will study transverse projective structures
and connections, and show that the derivative is in fact determined by the projective structure
and the family.
2014年04月15日(火)
16:30-18:00 数理科学研究科棟(駒場) 056号室
Tea: 16:00 - 16:30 コモンルーム
内藤 貴仁 氏 (東京大学大学院数理科学研究科)
On the rational string operations of classifying spaces and the
Hochschild cohomology (JAPANESE)
Tea: 16:00 - 16:30 コモンルーム
内藤 貴仁 氏 (東京大学大学院数理科学研究科)
On the rational string operations of classifying spaces and the
Hochschild cohomology (JAPANESE)
[ 講演概要 ]
Chataur and Menichi initiated the theory of string topology of
classifying spaces.
In particular, the cohomology of the free loop space of a classifying
space is endowed with a product
called the dual loop coproduct. In this talk, I will discuss the
algebraic structure and relate the rational dual loop coproduct to the
cup product on the Hochschild cohomology via the Van den Bergh isomorphism.
Chataur and Menichi initiated the theory of string topology of
classifying spaces.
In particular, the cohomology of the free loop space of a classifying
space is endowed with a product
called the dual loop coproduct. In this talk, I will discuss the
algebraic structure and relate the rational dual loop coproduct to the
cup product on the Hochschild cohomology via the Van den Bergh isomorphism.
