本文印刷
全画面プリント
トポロジー火曜セミナー
過去の記録 ～07/26｜次回の予定｜今後の予定 07/27～
| 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
2011年11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
河野俊丈 氏 (東京大学大学院数理科学研究科)
Quantum and homological representations of braid groups (JAPANESE)
Tea: 16:00 - 16:30 コモンルーム
河野俊丈 氏 (東京大学大学院数理科学研究科)
Quantum and homological representations of braid groups (JAPANESE)
[ 講演概要 ]
Homological representations of braid groups are defined as
the action of homeomorphisms of a punctured disk on
the homology of an abelian covering of its configuration space.
These representations were extensively studied by Lawrence,
Krammer and Bigelow. In this talk we show that specializations
of the homological representations of braid groups
are equivalent to the monodromy of the KZ equation with
values in the space of null vectors in the tensor product
of Verma modules when the parameters are generic.
To prove this we use representations of the solutions of the
KZ equation by hypergeometric integrals due to Schechtman,
Varchenko and others.
In the case of special parameters these representations
are extended to quantum representations of mapping
class groups. We describe the images of such representations
and show that the images of any Johnson subgroups
contain non-abelian free groups if the genus and the
level are sufficiently large. The last part is a joint
work with Louis Funar.
Homological representations of braid groups are defined as
the action of homeomorphisms of a punctured disk on
the homology of an abelian covering of its configuration space.
These representations were extensively studied by Lawrence,
Krammer and Bigelow. In this talk we show that specializations
of the homological representations of braid groups
are equivalent to the monodromy of the KZ equation with
values in the space of null vectors in the tensor product
of Verma modules when the parameters are generic.
To prove this we use representations of the solutions of the
KZ equation by hypergeometric integrals due to Schechtman,
Varchenko and others.
In the case of special parameters these representations
are extended to quantum representations of mapping
class groups. We describe the images of such representations
and show that the images of any Johnson subgroups
contain non-abelian free groups if the genus and the
level are sufficiently large. The last part is a joint
work with Louis Funar.
2011年11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
Francois Laudenbach 氏 (Univ. de Nantes)
Singular codimension-one foliations
and twisted open books in dimension 3.
(joint work with G. Meigniez)
(ENGLISH)
Tea: 16:00 - 16:30 コモンルーム
Francois Laudenbach 氏 (Univ. de Nantes)
Singular codimension-one foliations
and twisted open books in dimension 3.
(joint work with G. Meigniez)
(ENGLISH)
[ 講演概要 ]
The allowed singularities are those of functions.
According to A. Haefliger (1958),
such structures on manifolds, called $\\Gamma_1$-structures,
are objects of a cohomological
theory with a classifying space $B\\Gamma_1$.
The problem of cancelling the singularities
(or regularization problem)
arise naturally.
For a closed manifold, it was solved by W.Thurston in a famous paper
(1976), with a proof relying on Mather's isomorphism (1971):
Diff$^\\infty(\\mathbb R)$ as a discrete group has the same homology
as the based loop space
$\\Omega B\\Gamma_1^+$.
For further extension to contact geometry, it is necessary
to solve the regularization problem
without using Mather's isomorphism.
That is what we have done in dimension 3. Our result is the following.
{\\it Every $\\Gamma_1$-structure $\\xi$ on a 3-manifold $M$ whose
normal bundle
embeds into the tangent bundle to $M$ is $\\Gamma_1$-homotopic
to a regular foliation
carried by a (possibily twisted) open book.}
The proof is elementary and relies on the dynamics of a (twisted)
pseudo-gradient of $\\xi$.
All the objects will be defined in the talk, in particular the notion
of twisted open book which is a central object in the reported paper.
The allowed singularities are those of functions.
According to A. Haefliger (1958),
such structures on manifolds, called $\\Gamma_1$-structures,
are objects of a cohomological
theory with a classifying space $B\\Gamma_1$.
The problem of cancelling the singularities
(or regularization problem)
arise naturally.
For a closed manifold, it was solved by W.Thurston in a famous paper
(1976), with a proof relying on Mather's isomorphism (1971):
Diff$^\\infty(\\mathbb R)$ as a discrete group has the same homology
as the based loop space
$\\Omega B\\Gamma_1^+$.
For further extension to contact geometry, it is necessary
to solve the regularization problem
without using Mather's isomorphism.
That is what we have done in dimension 3. Our result is the following.
{\\it Every $\\Gamma_1$-structure $\\xi$ on a 3-manifold $M$ whose
normal bundle
embeds into the tangent bundle to $M$ is $\\Gamma_1$-homotopic
to a regular foliation
carried by a (possibily twisted) open book.}
The proof is elementary and relies on the dynamics of a (twisted)
pseudo-gradient of $\\xi$.
All the objects will be defined in the talk, in particular the notion
of twisted open book which is a central object in the reported paper.
2011年11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
與倉 昭治 氏 (鹿児島大学)
Fiberwise bordism groups and related topics (JAPANESE)
Tea: 16:00 - 16:30 コモンルーム
與倉 昭治 氏 (鹿児島大学)
Fiberwise bordism groups and related topics (JAPANESE)
[ 講演概要 ]
We have recently introduced the notion of fiberwise bordism. In this talk, after a quick review of some of the classical (co)bordism theories, we will explain motivations of considering fiberwise bordism and some results and connections with other known works, such as M. Kreck's bordism groups of orientation preserving diffeomorphisms and Emerson-Meyer's bivariant K-theory etc. An essential motivation is our recent work towards constructing a bivariant-theoretic analogue (in the sense of Fulton-MacPherson) of Levine-Morel's or Levine-Pandharipande's algebraic cobordism.
We have recently introduced the notion of fiberwise bordism. In this talk, after a quick review of some of the classical (co)bordism theories, we will explain motivations of considering fiberwise bordism and some results and connections with other known works, such as M. Kreck's bordism groups of orientation preserving diffeomorphisms and Emerson-Meyer's bivariant K-theory etc. An essential motivation is our recent work towards constructing a bivariant-theoretic analogue (in the sense of Fulton-MacPherson) of Levine-Morel's or Levine-Pandharipande's algebraic cobordism.
2011年11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
竹内 潔 氏 (筑波大学)
Motivic Milnor fibers and Jordan normal forms of monodromies (JAPANESE)
Tea: 16:00 - 16:30 コモンルーム
竹内 潔 氏 (筑波大学)
Motivic Milnor fibers and Jordan normal forms of monodromies (JAPANESE)
[ 講演概要 ]
We introduce a method to calculate the equivariant
Hodge-Deligne numbers of toric hypersurfaces.
Then we apply it to motivic Milnor
fibers introduced by Denef-Loeser and study the Jordan
normal forms of the local and global monodromies
of polynomials maps in various situations.
Especially we focus our attention on monodromies
at infinity studied by many people. The results will be
explicitly described by the ``convexity" of
the Newton polyhedra of polynomials. This is a joint work
with Y. Matsui and A. Esterov.
We introduce a method to calculate the equivariant
Hodge-Deligne numbers of toric hypersurfaces.
Then we apply it to motivic Milnor
fibers introduced by Denef-Loeser and study the Jordan
normal forms of the local and global monodromies
of polynomials maps in various situations.
Especially we focus our attention on monodromies
at infinity studied by many people. The results will be
explicitly described by the ``convexity" of
the Newton polyhedra of polynomials. This is a joint work
with Y. Matsui and A. Esterov.
2011年10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 コモンルーム
Andrei Pajitnov 氏 (Univ. de Nantes, Univ. of Tokyo)
Circle-valued Morse theory for complex hyperplane arrangements (ENGLISH)
Tea: 16:00 - 16:30 コモンルーム
Andrei Pajitnov 氏 (Univ. de Nantes, Univ. of Tokyo)
Circle-valued Morse theory for complex hyperplane arrangements (ENGLISH)
[ 講演概要 ]
Let A be a complex hyperplane arrangement
in an n-dimensional complex vector space V.
Denote by H the union of the hyperplanes
and by M the complement to H in V.
We develop the real-valued and circle-valued Morse
theory on M. We prove that if A is essential then
M has the homotopy type of a space
obtained from a finite n-dimensional
CW complex fibered over a circle,
by attaching several cells of dimension n.
We compute the Novikov homology of M and show
that its structure is similar to the
homology with generic local coefficients:
it vanishes for all dimensions except n.
This is a joint work with Toshitake Kohno.
Let A be a complex hyperplane arrangement
in an n-dimensional complex vector space V.
Denote by H the union of the hyperplanes
and by M the complement to H in V.
We develop the real-valued and circle-valued Morse
theory on M. We prove that if A is essential then
M has the homotopy type of a space
obtained from a finite n-dimensional
CW complex fibered over a circle,
by attaching several cells of dimension n.
We compute the Novikov homology of M and show
that its structure is similar to the
homology with generic local coefficients:
it vanishes for all dimensions except n.
This is a joint work with Toshitake Kohno.
2011年10月11日(火)
17:00-18:00 数理科学研究科棟(駒場) 056号室
Tea: 16:40 - 17:00 コモンルーム
Gael Meigniez 氏 (Univ. de Bretagne-Sud, Chuo Univ.)
Making foliations of codimension one,
thirty years after Thurston's works
(ENGLISH)
Tea: 16:40 - 17:00 コモンルーム
Gael Meigniez 氏 (Univ. de Bretagne-Sud, Chuo Univ.)
Making foliations of codimension one,
thirty years after Thurston's works
(ENGLISH)
[ 講演概要 ]
In 1976 Thurston proved that every closed manifold M whose
Euler characteristic is null carries a smooth foliation F of codimension
one. He actually established a h-principle allowing the regularization of
Haefliger structures through homotopy. I shall give some accounts of a new,
simpler proof of Thurston's result, not using Mather's homology equivalence; and also show that this proof allows to make F have dense leaves if dim M is at least 4. The emphasis will be put on the high dimensions.
In 1976 Thurston proved that every closed manifold M whose
Euler characteristic is null carries a smooth foliation F of codimension
one. He actually established a h-principle allowing the regularization of
Haefliger structures through homotopy. I shall give some accounts of a new,
simpler proof of Thurston's result, not using Mather's homology equivalence; and also show that this proof allows to make F have dense leaves if dim M is at least 4. The emphasis will be put on the high dimensions.
2011年10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 コモンルーム
松田 能文 氏 (東京大学大学院数理科学研究科)
相対的双曲群の相対的擬凸部分群 (JAPANESE)
Tea: 16:00 - 16:30 コモンルーム
松田 能文 氏 (東京大学大学院数理科学研究科)
相対的双曲群の相対的擬凸部分群 (JAPANESE)
[ 講演概要 ]
群の相対的双曲性は語双曲性の一般化としてGromovにより導入された. 相対的
双曲群の例として, 有限体積を持つ完備双曲多様体の基本群が挙げられる. 語双
曲群の擬凸部分群の一般化として, 相対的双曲群の相対的擬凸部分群が定義され
る. Osinにより相対的双曲群の双曲的に埋め込まれた部分群が導入され, 付加的
な代数的性質を持つ相対的擬凸部分群として特徴づけられている. この講演では,
相対的擬凸部分群を紹介するとともに双曲的に埋め込まれた部分群に関する尾
國新一氏, 山形紗恵子氏との最近の共同研究について触れる.
群の相対的双曲性は語双曲性の一般化としてGromovにより導入された. 相対的
双曲群の例として, 有限体積を持つ完備双曲多様体の基本群が挙げられる. 語双
曲群の擬凸部分群の一般化として, 相対的双曲群の相対的擬凸部分群が定義され
る. Osinにより相対的双曲群の双曲的に埋め込まれた部分群が導入され, 付加的
な代数的性質を持つ相対的擬凸部分群として特徴づけられている. この講演では,
相対的擬凸部分群を紹介するとともに双曲的に埋め込まれた部分群に関する尾
國新一氏, 山形紗恵子氏との最近の共同研究について触れる.
2011年09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
Clara Loeh 氏 (Univ. Regensburg)
Functorial semi-norms on singular homology (ENGLISH)
Tea: 16:00 - 16:30 コモンルーム
Clara Loeh 氏 (Univ. Regensburg)
Functorial semi-norms on singular homology (ENGLISH)
[ 講演概要 ]
Functorial semi-norms on singular homology add metric information to
homology classes that is compatible with continuous maps. In particular,
functorial semi-norms give rise to degree theorems for certain classes
of manifolds; an invariant fitting into this context is Gromov's
simplicial volume. On the other hand, knowledge about mapping degrees
allows to construct functorial semi-norms with interesting properties;
for example, so-called inflexible simply connected manifolds give rise
to functorial semi-norms that are non-trivial on certain simply connected
spaces.
Functorial semi-norms on singular homology add metric information to
homology classes that is compatible with continuous maps. In particular,
functorial semi-norms give rise to degree theorems for certain classes
of manifolds; an invariant fitting into this context is Gromov's
simplicial volume. On the other hand, knowledge about mapping degrees
allows to construct functorial semi-norms with interesting properties;
for example, so-called inflexible simply connected manifolds give rise
to functorial semi-norms that are non-trivial on certain simply connected
spaces.
2011年07月12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
川室 圭子 氏 (University of Iowa)
The self linking number and planar open book decomposition (ENGLISH)
Tea: 16:00 - 16:30 コモンルーム
川室 圭子 氏 (University of Iowa)
The self linking number and planar open book decomposition (ENGLISH)
[ 講演概要 ]
I will show a self linking number formula, in language of
braids, for transverse knots in contact manifolds that admit planar
open book decompositions. Our formula extends the Bennequin's for
the standar contact 3-sphere.
I will show a self linking number formula, in language of
braids, for transverse knots in contact manifolds that admit planar
open book decompositions. Our formula extends the Bennequin's for
the standar contact 3-sphere.
2011年07月05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
Catherine Oikonomides 氏 (東京大学大学院数理科学研究科, JSPS)
The C*-algebra of codimension one foliations which
are almost without holonomy (ENGLISH)
Tea: 16:00 - 16:30 コモンルーム
Catherine Oikonomides 氏 (東京大学大学院数理科学研究科, JSPS)
The C*-algebra of codimension one foliations which
are almost without holonomy (ENGLISH)
[ 講演概要 ]
Foliation C*-algebras have been defined abstractly by Alain Connes,
in the 1980s, as part of the theory of Noncommutative Geometry.
However, very few concrete examples of foliation C*-algebras
have been studied until now.
In this talk, we want to explain how to compute
the K-theory of the C*-algebra of codimension
one foliations which are "almost without holonomy",
meaning that the holonomy of all the noncompact leaves
of the foliation is trivial. Such foliations have a fairly
simple geometrical structure, which is well known thanks
to theorems by Imanishi, Hector and others. We will give some
concrete examples on 3-manifolds, in particular the 3-sphere
with the Reeb foliation, and also some slighty more
complicated examples.
Foliation C*-algebras have been defined abstractly by Alain Connes,
in the 1980s, as part of the theory of Noncommutative Geometry.
However, very few concrete examples of foliation C*-algebras
have been studied until now.
In this talk, we want to explain how to compute
the K-theory of the C*-algebra of codimension
one foliations which are "almost without holonomy",
meaning that the holonomy of all the noncompact leaves
of the foliation is trivial. Such foliations have a fairly
simple geometrical structure, which is well known thanks
to theorems by Imanishi, Hector and others. We will give some
concrete examples on 3-manifolds, in particular the 3-sphere
with the Reeb foliation, and also some slighty more
complicated examples.
2011年06月28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
二木 昌宏 氏 (東京大学大学院数理科学研究科)
On a Sebastiani-Thom theorem for directed Fukaya categories (JAPANESE)
Tea: 16:00 - 16:30 コモンルーム
二木 昌宏 氏 (東京大学大学院数理科学研究科)
On a Sebastiani-Thom theorem for directed Fukaya categories (JAPANESE)
[ 講演概要 ]
2011年06月14日(火)
17:00-18:00 数理科学研究科棟(駒場) 056号室
Tea: 16:40 - 17:00 コモンルーム
満渕 俊樹 氏 (大阪大学大学院理学研究科)
Donaldson-Tian-Yau's Conjecture (JAPANESE)
Tea: 16:40 - 17:00 コモンルーム
満渕 俊樹 氏 (大阪大学大学院理学研究科)
Donaldson-Tian-Yau's Conjecture (JAPANESE)
[ 講演概要 ]
For polarized algebraic manifolds, the concept of K-stability
introduced by Tian and Donaldson is conjecturally strongly correlated
to the existence of constant scalar curvature metrics (or more
generally extremal K\\"ahler metrics) in the polarization class. This is
known as Donaldson-Tian-Yau's conjecture. Recently, a remarkable
progress has been made by many authors toward its solution. In this
talk, I'll discuss the topic mainly with emphasis on the existence
part of the conjecture.
For polarized algebraic manifolds, the concept of K-stability
introduced by Tian and Donaldson is conjecturally strongly correlated
to the existence of constant scalar curvature metrics (or more
generally extremal K\\"ahler metrics) in the polarization class. This is
known as Donaldson-Tian-Yau's conjecture. Recently, a remarkable
progress has been made by many authors toward its solution. In this
talk, I'll discuss the topic mainly with emphasis on the existence
part of the conjecture.
2011年06月07日(火)
16:30-18:00 数理科学研究科棟(駒場) 056号室
Lie群論・表現論セミナーと合同 Tea: 16:00 - 16:30 コモンルーム
金井 雅彦 氏 (東京大学大学院数理科学研究科)
Rigidity of group actions via invariant geometric structures (JAPANESE)
Lie群論・表現論セミナーと合同 Tea: 16:00 - 16:30 コモンルーム
金井 雅彦 氏 (東京大学大学院数理科学研究科)
Rigidity of group actions via invariant geometric structures (JAPANESE)
[ 講演概要 ]
It is a homomorphism into a FINITE dimensional Lie group that is concerned with in the classical RIGIDITY theorems such as those of Mostow and Margulis. In the meantime, differentiable GROUP ACTIONS for which we ask rigidity problems is a homomorphism into a diffeomorphism group, which is a typical example of INFINITE dimensional Lie groups. The purpose of the present talk is exhibiting several rigidity theorems for group actions in which I have been involved for years. Although quite a few fields of mathematics, such as ergodic theory, the theory of smooth dynamical systems, representation theory and so on, have made remarkable contributions to rigidity problems, I would rather emphasis geometric aspects: I would focus on those rigidity phenomenon for group actions that are observed by showing that the actions have INVARIANT GEOMETRIC STRUCTURES.
It is a homomorphism into a FINITE dimensional Lie group that is concerned with in the classical RIGIDITY theorems such as those of Mostow and Margulis. In the meantime, differentiable GROUP ACTIONS for which we ask rigidity problems is a homomorphism into a diffeomorphism group, which is a typical example of INFINITE dimensional Lie groups. The purpose of the present talk is exhibiting several rigidity theorems for group actions in which I have been involved for years. Although quite a few fields of mathematics, such as ergodic theory, the theory of smooth dynamical systems, representation theory and so on, have made remarkable contributions to rigidity problems, I would rather emphasis geometric aspects: I would focus on those rigidity phenomenon for group actions that are observed by showing that the actions have INVARIANT GEOMETRIC STRUCTURES.
2011年05月31日(火)
17:00-18:00 数理科学研究科棟(駒場) 056号室
Tea: 16:40 - 17:00 コモンルーム
盛田 健彦 氏 (大阪大学大学院理学研究科)
Measures with maximum total exponent and generic properties of $C^
{1}$ expanding maps (JAPANESE)
Tea: 16:40 - 17:00 コモンルーム
盛田 健彦 氏 (大阪大学大学院理学研究科)
Measures with maximum total exponent and generic properties of $C^
{1}$ expanding maps (JAPANESE)
[ 講演概要 ]
This is a joint work with Yusuke Tokunaga. Let $M$ be an $N$
dimensional compact connected smooth Riemannian manifold without
boundary and let $\\mathcal{E}^{r}(M,M)$ be the space of $C^{r}$
expandig maps endowed with $C^{r}$ topology. We show that
each of the following properties for element $T$ in $\\mathcal{E}
^{1}(M,M)$ is generic.
\\begin{itemize}
\\item[(1)] $T$ has a unique measure with maximum total exponent.
\\item[(2)] Any measure with maximum total exponent for $T$ has
zero entropy.
\\item[(3)] Any measure with maximum total exponent for $T$ is
fully supported.
\\end{itemize}
On the contrary, we show that for $r\\ge 2$, a generic element
in $\\mathcal{E}^{r}(M,M)$ has no fully supported measures with
maximum total exponent.
This is a joint work with Yusuke Tokunaga. Let $M$ be an $N$
dimensional compact connected smooth Riemannian manifold without
boundary and let $\\mathcal{E}^{r}(M,M)$ be the space of $C^{r}$
expandig maps endowed with $C^{r}$ topology. We show that
each of the following properties for element $T$ in $\\mathcal{E}
^{1}(M,M)$ is generic.
\\begin{itemize}
\\item[(1)] $T$ has a unique measure with maximum total exponent.
\\item[(2)] Any measure with maximum total exponent for $T$ has
zero entropy.
\\item[(3)] Any measure with maximum total exponent for $T$ is
fully supported.
\\end{itemize}
On the contrary, we show that for $r\\ge 2$, a generic element
in $\\mathcal{E}^{r}(M,M)$ has no fully supported measures with
maximum total exponent.
2011年05月24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
吉永 正彦 氏 (京都大学大学院理学研究科)
Minimal Stratifications for Line Arrangements (JAPANESE)
Tea: 16:00 - 16:30 コモンルーム
吉永 正彦 氏 (京都大学大学院理学研究科)
Minimal Stratifications for Line Arrangements (JAPANESE)
[ 講演概要 ]
The homotopy type of complements of complex
hyperplane arrangements have a special property,
so called minimality (Dimca-Papadima and Randell,
around 2000). Since then several approaches based
on (continuous, discrete) Morse theory have appeared.
In this talk, we introduce the "dual" object, which we
call minimal stratification for real two dimensional cases.
A merit is that the minimal stratification can be explicitly
described in terms of semi-algebraic sets.
We also see associated presentation of the fundamental group.
The homotopy type of complements of complex
hyperplane arrangements have a special property,
so called minimality (Dimca-Papadima and Randell,
around 2000). Since then several approaches based
on (continuous, discrete) Morse theory have appeared.
In this talk, we introduce the "dual" object, which we
call minimal stratification for real two dimensional cases.
A merit is that the minimal stratification can be explicitly
described in terms of semi-algebraic sets.
We also see associated presentation of the fundamental group.
2011年05月17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
石井 敦 氏 (筑波大学 大学院数理物質科学研究科)
Quandle colorings with non-commutative flows (JAPANESE)
Tea: 16:00 - 16:30 コモンルーム
石井 敦 氏 (筑波大学 大学院数理物質科学研究科)
Quandle colorings with non-commutative flows (JAPANESE)
[ 講演概要 ]
This is a joint work with Masahide Iwakiri, Yeonhee Jang and Kanako Oshiro.
We introduce quandle coloring invariants and quandle cocycle invariants
with non-commutative flows for knots, spatial graphs, handlebody-knots,
where a handlebody-knot is a handlebody embedded in the $3$-sphere.
Two handlebody-knots are equivalent if one can be transformed into the
other by an isotopy of $S^3$.
The quandle coloring (resp. cocycle) invariant is a ``twisted'' quandle
coloring (resp. cocycle) invariant.
This is a joint work with Masahide Iwakiri, Yeonhee Jang and Kanako Oshiro.
We introduce quandle coloring invariants and quandle cocycle invariants
with non-commutative flows for knots, spatial graphs, handlebody-knots,
where a handlebody-knot is a handlebody embedded in the $3$-sphere.
Two handlebody-knots are equivalent if one can be transformed into the
other by an isotopy of $S^3$.
The quandle coloring (resp. cocycle) invariant is a ``twisted'' quandle
coloring (resp. cocycle) invariant.
2011年05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
伊藤 哲也 氏 (東京大学大学院数理科学研究科)
Isotated points in the space of group left orderings (JAPANESE)
Tea: 16:00 - 16:30 コモンルーム
伊藤 哲也 氏 (東京大学大学院数理科学研究科)
Isotated points in the space of group left orderings (JAPANESE)
[ 講演概要 ]
The set of all left orderings of a group G admits a natural
topology. In general the space of left orderings is homeomorphic to the
union of Cantor set and finitely many isolated points. In this talk I
will give a new method to construct left orderings corresponding to
isolated points, and will explain how such isolated orderings reflect
the structures of groups.
The set of all left orderings of a group G admits a natural
topology. In general the space of left orderings is homeomorphic to the
union of Cantor set and finitely many isolated points. In this talk I
will give a new method to construct left orderings corresponding to
isolated points, and will explain how such isolated orderings reflect
the structures of groups.
2011年04月26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, Lie群論・表現論セミナーと合同
吉野 太郎 氏 (東京大学大学院数理科学研究科)
Topological Blow-up (JAPANESE)
Tea: 16:00 - 16:30 コモンルーム, Lie群論・表現論セミナーと合同
吉野 太郎 氏 (東京大学大学院数理科学研究科)
Topological Blow-up (JAPANESE)
[ 講演概要 ]
Suppose that a Lie group $G$ acts on a manifold
$M$. The quotient space $X:=G\\backslash M$ is locally compact,
but not Hausdorff in general. Our aim is to understand
such a non-Hausdorff space $X$.
The space $X$ has the crack $S$. Roughly speaking, $S$ is
the causal subset of non-Hausdorffness of $X$, and especially
$X\\setminus S$ is Hausdorff.
We introduce the concept of `topological blow-up' as a `repair'
of the crack. The `repaired' space $\\tilde{X}$ is
locally compact and Hausdorff space containing $X\\setminus S$
as its open subset. Moreover, the original space $X$ can be
recovered from the pair of $(\\tilde{X}, S)$.
Suppose that a Lie group $G$ acts on a manifold
$M$. The quotient space $X:=G\\backslash M$ is locally compact,
but not Hausdorff in general. Our aim is to understand
such a non-Hausdorff space $X$.
The space $X$ has the crack $S$. Roughly speaking, $S$ is
the causal subset of non-Hausdorffness of $X$, and especially
$X\\setminus S$ is Hausdorff.
We introduce the concept of `topological blow-up' as a `repair'
of the crack. The `repaired' space $\\tilde{X}$ is
locally compact and Hausdorff space containing $X\\setminus S$
as its open subset. Moreover, the original space $X$ can be
recovered from the pair of $(\\tilde{X}, S)$.
2011年04月12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
廣瀬 進 氏 (東京理科大学理工学部数学科)
On diffeomorphisms over non-orientable surfaces embedded in the 4-sphere (JAPANESE)
Tea: 16:00 - 16:30 コモンルーム
廣瀬 進 氏 (東京理科大学理工学部数学科)
On diffeomorphisms over non-orientable surfaces embedded in the 4-sphere (JAPANESE)
[ 講演概要 ]
4次元球面内に標準的に埋め込まれた向き付け可能曲面上の
向きを保つ可微分同相写像が向きを保つ4次元球面上の可微分同相写像に
拡張できるための必要十分条件は,その曲面に対する Rokhlin の2次形式を
保つことであることが知られている.
本講演では,向き付け不可能な閉曲面に対する同様の問題についての
現在進行中の試みについて話す.
4次元球面内に標準的に埋め込まれた向き付け可能曲面上の
向きを保つ可微分同相写像が向きを保つ4次元球面上の可微分同相写像に
拡張できるための必要十分条件は,その曲面に対する Rokhlin の2次形式を
保つことであることが知られている.
本講演では,向き付け不可能な閉曲面に対する同様の問題についての
現在進行中の試みについて話す.
2011年01月25日(火)
16:30-17:30 数理科学研究科棟(駒場) 056号室
Tea: 16:00 - 16:30 コモンルーム
春田 力 氏 (東京大学大学院数理科学研究科)
シート数が小さい曲面結び目の自明化について (JAPANESE)
Tea: 16:00 - 16:30 コモンルーム
春田 力 氏 (東京大学大学院数理科学研究科)
シート数が小さい曲面結び目の自明化について (JAPANESE)
[ 講演概要 ]
A connected surface smoothly embedded in ${\\mathbb R}^4$ is called a surface-knot. In particular, if a surface-knot $F$ is homeomorphic to the $2$-sphere or the torus, then it is called an $S^2$-knot or a $T^2$-knot, respectively. The sheet number of a surface-knot is an invariant analogous to the crossing number of a $1$-knot. M. Saito and S. Satoh proved some results concerning the sheet number of an $S^2$-knot. In particular, it is known that an $S^2$-knot is trivial if and only if its sheet number is $1$, and there is no $S^2$-knot whose sheet number is $2$. In this talk, we show that there is no $S^2$-knot whose sheet number is $3$, and a $T^2$-knot is trivial if and only if its sheet number is $1$.
A connected surface smoothly embedded in ${\\mathbb R}^4$ is called a surface-knot. In particular, if a surface-knot $F$ is homeomorphic to the $2$-sphere or the torus, then it is called an $S^2$-knot or a $T^2$-knot, respectively. The sheet number of a surface-knot is an invariant analogous to the crossing number of a $1$-knot. M. Saito and S. Satoh proved some results concerning the sheet number of an $S^2$-knot. In particular, it is known that an $S^2$-knot is trivial if and only if its sheet number is $1$, and there is no $S^2$-knot whose sheet number is $2$. In this talk, we show that there is no $S^2$-knot whose sheet number is $3$, and a $T^2$-knot is trivial if and only if its sheet number is $1$.
2011年01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 コモンルーム
河澄 響矢 氏 (東京大学大学院数理科学研究科)
The Chas-Sullivan conjecture for a surface of infinite genus (JAPANESE)
Tea: 16:00 - 16:30 コモンルーム
河澄 響矢 氏 (東京大学大学院数理科学研究科)
The Chas-Sullivan conjecture for a surface of infinite genus (JAPANESE)
[ 講演概要 ]
久野雄介氏(広島大理、学振PD)との共同研究。
\\Sigma_{\\infty,1} を境界成分 1 の向きづけられたコンパクト曲面の
帰納極限とする。この曲面 \\Sigma_{\\infty,1} の Goldman Lie 代数
の中心が定数ループで張られることを証明する。閉曲面についての
同様の定理を Chas と Sullivan が予想し、Etingof が証明している。
我々の結果は向きづけられたコード図式の Lie 代数の中心を計算
することで証明される。時間が許せば、線型コード図式の空間上の
Lie 代数の構造についても議論したい。
久野雄介氏(広島大理、学振PD)との共同研究。
\\Sigma_{\\infty,1} を境界成分 1 の向きづけられたコンパクト曲面の
帰納極限とする。この曲面 \\Sigma_{\\infty,1} の Goldman Lie 代数
の中心が定数ループで張られることを証明する。閉曲面についての
同様の定理を Chas と Sullivan が予想し、Etingof が証明している。
我々の結果は向きづけられたコード図式の Lie 代数の中心を計算
することで証明される。時間が許せば、線型コード図式の空間上の
Lie 代数の構造についても議論したい。
2010年12月14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
Kenneth Schackleton 氏 (IPMU)
On the coarse geometry of Teichmueller space (ENGLISH)
Tea: 16:00 - 16:30 コモンルーム
Kenneth Schackleton 氏 (IPMU)
On the coarse geometry of Teichmueller space (ENGLISH)
[ 講演概要 ]
We discuss the synthetic geometry of the pants graph in
comparison with the Weil-Petersson metric, whose geometry the
pants graph coarsely models following work of Brock’s. We also
restrict our attention to the 5-holed sphere, studying the Gromov
bordification of the pants graph and the dynamics of pseudo-Anosov
mapping classes.
We discuss the synthetic geometry of the pants graph in
comparison with the Weil-Petersson metric, whose geometry the
pants graph coarsely models following work of Brock’s. We also
restrict our attention to the 5-holed sphere, studying the Gromov
bordification of the pants graph and the dynamics of pseudo-Anosov
mapping classes.
2010年12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
Raphael Ponge 氏 (東京大学大学院数理科学研究科)
Diffeomorphism-invariant geometries and noncommutative geometry (ENGLISH)
Tea: 16:00 - 16:30 コモンルーム
Raphael Ponge 氏 (東京大学大学院数理科学研究科)
Diffeomorphism-invariant geometries and noncommutative geometry (ENGLISH)
[ 講演概要 ]
In many geometric situations we may encounter the action of
a group $G$ on a manifold $M$, e.g., in the context of foliations. If
the action is free and proper, then the quotient $M/G$ is a smooth
manifold. However, in general the quotient $M/G$ need not even be
Hausdorff. Furthermore, it is well-known that a manifold has structure
invariant under the full group of diffeomorphisms except the
differentiable structure itself. Under these conditions how can one do
diffeomorphism-invariant geometry?
Noncommutative geometry provides us with the solution of trading the
ill-behaved space $M/G$ for a non-commutative algebra which
essentially plays the role of the algebra of smooth functions on that
space. The local index formula of Atiyah-Singer ultimately holds in
the setting of noncommutative geometry. Using this framework Connes
and Moscovici then obtained in the 90s a striking reformulation of the
local index formula in diffeomorphism-invariant geometry.
An important part the talk will be devoted to reviewing noncommutative
geometry and Connes-Moscovici's index formula. We will then hint to on-
going projects about reformulating the local index formula in two new
geometric settings: biholomorphism-invariant geometry of strictly
pseudo-convex domains and contactomorphism-invariant geometry.
In many geometric situations we may encounter the action of
a group $G$ on a manifold $M$, e.g., in the context of foliations. If
the action is free and proper, then the quotient $M/G$ is a smooth
manifold. However, in general the quotient $M/G$ need not even be
Hausdorff. Furthermore, it is well-known that a manifold has structure
invariant under the full group of diffeomorphisms except the
differentiable structure itself. Under these conditions how can one do
diffeomorphism-invariant geometry?
Noncommutative geometry provides us with the solution of trading the
ill-behaved space $M/G$ for a non-commutative algebra which
essentially plays the role of the algebra of smooth functions on that
space. The local index formula of Atiyah-Singer ultimately holds in
the setting of noncommutative geometry. Using this framework Connes
and Moscovici then obtained in the 90s a striking reformulation of the
local index formula in diffeomorphism-invariant geometry.
An important part the talk will be devoted to reviewing noncommutative
geometry and Connes-Moscovici's index formula. We will then hint to on-
going projects about reformulating the local index formula in two new
geometric settings: biholomorphism-invariant geometry of strictly
pseudo-convex domains and contactomorphism-invariant geometry.
2010年11月30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
中村 信裕 氏 (東京大学大学院数理科学研究科)
Pin^-(2)-monopole equations and intersection forms with local coefficients of 4-manifolds (JAPANESE)
Tea: 16:00 - 16:30 コモンルーム
中村 信裕 氏 (東京大学大学院数理科学研究科)
Pin^-(2)-monopole equations and intersection forms with local coefficients of 4-manifolds (JAPANESE)
[ 講演概要 ]
We introduce a variant of the Seiberg-Witten equations, Pin^-(2)-monopole equations, and explain its applications to intersection forms with local coefficients of 4-manifolds.
The first application is an analogue of Froyshov's results on 4-manifolds which have definite forms with local coefficients.
The second one is a local coefficient version of Furuta's 10/8-inequality.
As a corollary, we construct nonsmoothable spin 4-manifolds satisfying Rohlin's theorem and the 10/8-inequality.
We introduce a variant of the Seiberg-Witten equations, Pin^-(2)-monopole equations, and explain its applications to intersection forms with local coefficients of 4-manifolds.
The first application is an analogue of Froyshov's results on 4-manifolds which have definite forms with local coefficients.
The second one is a local coefficient version of Furuta's 10/8-inequality.
As a corollary, we construct nonsmoothable spin 4-manifolds satisfying Rohlin's theorem and the 10/8-inequality.
2010年11月16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
伊藤 昇 氏 (早稲田大学)
On a colored Khovanov bicomplex (JAPANESE)
Tea: 16:00 - 16:30 コモンルーム
伊藤 昇 氏 (早稲田大学)
On a colored Khovanov bicomplex (JAPANESE)
[ 講演概要 ]
Jones 多項式の Khovanov ホモロジーと関連理論が近年活発に
研究されている.Jons 多項式の一般化である colored Jones多項式についても
Khovanov により対応するコホモロジーが導入され,特に Mackaay と Turner
や Beliakova とWehrli の研究を通し発展した.しかし,このコホモロジーが持つ
2つの境界作用素によって,Khovanov型の複体で2重複体となるものが構成
できるのかは問題として残されていた.もしあるならば Khovanov 型のホモロジーが
Total complexのコホモロジーに収束するスペクトル系列の第2項として理解される.
この問題意識は Beliakova と Wehliの論文によって紹介された.今回はそれに
対して一つの答えを与える.また似た文脈で colored Jones 多項式の別のスペクトル
系列からは絡み目のcolored Rasmussen 不変量が自然に出てくることも時間が許せば
紹介したい.
Jones 多項式の Khovanov ホモロジーと関連理論が近年活発に
研究されている.Jons 多項式の一般化である colored Jones多項式についても
Khovanov により対応するコホモロジーが導入され,特に Mackaay と Turner
や Beliakova とWehrli の研究を通し発展した.しかし,このコホモロジーが持つ
2つの境界作用素によって,Khovanov型の複体で2重複体となるものが構成
できるのかは問題として残されていた.もしあるならば Khovanov 型のホモロジーが
Total complexのコホモロジーに収束するスペクトル系列の第2項として理解される.
この問題意識は Beliakova と Wehliの論文によって紹介された.今回はそれに
対して一つの答えを与える.また似た文脈で colored Jones 多項式の別のスペクトル
系列からは絡み目のcolored Rasmussen 不変量が自然に出てくることも時間が許せば
紹介したい.
