トポロジー火曜セミナー

過去の記録 ~09/24次回の予定今後の予定 09/25~

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 河野 俊丈, 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
備考 Tea: 16:30 - 17:00 コモンルーム

過去の記録

2015年06月16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
石川 昌治 氏 (東北大学)
Stable maps and branched shadows of 3-manifolds (JAPANESE)
[ 講演概要 ]
We study what kind of stable map to the real plane a 3-manifold has. It
is known by O. Saeki that there exists a stable map without certain
singular fibers if and only if the 3-manifold is a graph manifold. According to
F. Costantino and D. Thurston, we identify the Stein factorization of a
stable map with a shadow of the 3-manifold under some modification,
where the above singular fibers correspond to the vertices of the shadow. We
define the notion of stable map complexity by counting the number of
such singular fibers and prove that this equals the branched shadow
complexity. With this equality, we give an estimation of the Gromov norm of the
3-manifold by the stable map complexity. This is a joint work with Yuya Koda.

2015年06月09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
赤穂 まなぶ 氏 (首都大学東京)
完全ラグランジュはめ込みのシンプレクティックdisplacementエネルギーについて (JAPANESE)
[ 講演概要 ]
この講演では完全ラグランジュはめ込みのdisplacementエネルギーと擬正則円盤
のシンプレクティック面積に関するある不等式を与える. 証明はChekanovが有理
ラグランジュ部分多様体のdisplacementエネルギーに関する不等式を示す際に用
いた技法を, ラグランジュはめ込みのFloerホモロジーに拡張して行う. また時
間が許せば, 我々の不等式とHofer--Zehnderのシンプレクティック容量に関する
考察を述べる.

2015年05月26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
久我 健一 氏 (千葉大学)
Introduction to formalization of topology using a proof assistant. (JAPANESE)
[ 講演概要 ]
Although the program of formalization goes back to David
Hilbert, it is only recently that we can actually formalize
substantial theorems in modern mathematics. It is made possible by the
development of certain type theory and a computer software called a
proof assistant. We begin this talk by showing our formalization of
some basic geometric topology using a proof assistant COQ. Then we
introduce homotopy type theory (HoTT) of Voevodsky et al., which
interprets type theory from abstract homotopy theoretic perspective.
HoTT proposes "univalent" foundation of mathematics which is
particularly suited for computer formalization.

2015年05月19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
加藤 晃史 氏 (東京大学大学院数理科学研究科)
Quiver mutation loops and partition q-series (JAPANESE)
[ 講演概要 ]
Quivers and their mutations are ubiquitous in mathematics and
mathematical physics; they play a key role in cluster algebras,
wall-crossing phenomena, gluing of ideal tetrahedra, etc.
Recently, we introduced a partition q-series for a quiver mutation loop
(a loop in a quiver exchange graph) using the idea of state sum of statistical
mechanics. The partition q-series enjoy some nice properties such
as pentagon move invariance. We also discuss their relation with combinatorial
Donaldson-Thomas invariants, as well as fermionic character formulas of
certain conformal field theories.
This is a joint work with Yuji Terashima.

2015年05月12日(火)

17:30-18:30   数理科学研究科棟(駒場) 056号室
Tea : 17:00-17:30 Common Room
浅岡 正幸 氏 (京都大学)
genericな力学系の周期点の個数の増大度 (JAPANESE)
[ 講演概要 ]
双曲力学系と呼ばれる統計的によい振る舞いをする力学系に関しては,
その周期軌道の数の増大度は常に高々指数的で,増大度は系の統計的
性質と密接に関係することが知られている.一方で1999年にKaloshin
により,homoclinic接触と呼ばれる複雑な分岐現象が稠密に起きるよ
うな領域においてはgenericな力学系はその周期軌道の数の増大度は
指数的よりも速くなることが証明されている.

では,弱い双曲性を持ち,homoclinic接触からは離れている「部分双
曲系」と呼ばれる系において周期点の数の増大度がどう振る舞うだ
ろうか.双曲力学系と同様に高々指数的になるだろうか,それとも,
homoclinic 接触とは異なるメカニズムによって,指数的よりも速く
なるだろうか?

講演者は,篠原克寿氏とDimitry Turaev氏との共同研究によって,
部分双曲系のダイナミクスのある種の単純化である「区間上の反復
函数系」において,ある自然な条件の元でその周期軌道の数がgeneric
には指数的よりも速く増大することを証明した.本講演では,力学
系の周期軌道の増大度の問題の歴史の概観した後,指数的よりも速
い増大度を引き起こすメカニズムについて,Kaloshinが見つけた
homoclinic接触によるものと講演者たちが見つけたものを対比しつ
つ解説したい.

2015年05月07日(木)

17:00-18:30   数理科学研究科棟(駒場) 056号室
This seminar will be held on Thursdsay.
Patrick Dehornoy 氏 (Univ. de Caen)
The group of parenthesized braids (ENGLISH)
[ 講演概要 ]
We describe a group B obtained by gluing in a natural way two well-known
groups, namely Artin's braid group B_infty and Thompson's group F. The
elements of B correspond to braid diagrams in which the distances
between the strands are non uniform and some rescaling operators may
change these distances. The group B shares many properties with B_infty:
as the latter, it can be realized as a subgroup of a mapping class
group, namely that of a sphere with a Cantor set removed, and as a group
of automorphisms of a free group. Technically, the key point is the
existence of a self-distributive operation on B.

2015年04月28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
正井 秀俊 氏 (東京大学大学院数理科学研究科, JSPS)
Verify hyperbolicity of 3-manifolds by computer and its applications. (JAPANESE)
[ 講演概要 ]
In this talk I will talk about the program called HIKMOT which
rigorously proves hyperbolicity of a given triangulated 3-manifold. To
prove hyperbolicity of a given triangulated 3-manifold, it suffices to
get a solution of Thurston's gluing equation. We use the notion called
interval arithmetic to overcome two types errors; round-off errors,
and truncated errors. I will also talk about its application to
exceptional surgeries along alternating knots. This talk is based on
joint work with N. Hoffman, K. Ichihara, M. Kashiwagi, S. Oishi, and
A. Takayasu.

2015年04月21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
木田 良才 氏 (東京大学大学院数理科学研究科)
Orbit equivalence relations arising from Baumslag-Solitar groups (JAPANESE)
[ 講演概要 ]
This talk is about measure-preserving actions of countable groups on probability
measure spaces and their orbit structure. Two such actions are called orbit equivalent
if there exists an isomorphism between the spaces preserving orbits. In this talk, I focus
on actions of Baumslag-Solitar groups that have two generators, a and t, with the relation
ta^p=a^qt, where p and q are given integers. This group is well studied in combinatorial
and geometric group theory. Whether Baumslag-Solitar groups with different p and q can
have orbit-equivalent actions is still a big open problem. I will discuss invariants under
orbit equivalence, motivating background and some results toward this problem.

2015年04月14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
中村 信裕 氏 (学習院大学)
Pin(2)-monopole invariants for 4-manifolds (JAPANESE)
[ 講演概要 ]
The Pin(2)-monopole equations are a variant of the Seiberg-Witten equations
which can be considered as a real version of the SW equations. A Pin(2)-mono
pole version of the Seiberg-Witten invariants is defined, and a special feature of
this is that the Pin(2)-monopole invariant can be nontrivial even when all of
the Donaldson and Seiberg-Witten invariants vanish. As an application, we
construct a new series of exotic 4-manifolds.

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)
[ 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.

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)
[ 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.

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)
[ 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.

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)
[ 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.

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)
[ 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.

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)
[ 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.

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)
[ 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.

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)
[ 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.

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)
[ 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.

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)
[ 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.

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)
[ 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.

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)
[ 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.

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)
[ 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.

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)
[ 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.

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)
[ 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.

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)
[ 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."

< 前へ 123456789101112131415161718 次へ >