17:00 -- 18:30 数理科学研究科棟(東京大学駒場キャンパス)
Tea: 16:30 -- 17:00 コモンルーム

Last updated November 25, 2016
河野 俊丈
河澄 響矢
北山 貴裕
逆井 卓也

9月27日 -- 056号室, 17:00 -- 18:30

藤内 翔太 (東京大学大学院数理科学研究科)

CAT(0) properties for orthoscheme complexes

Abstract: Gromov showed that a cubical complex is locally CAT(0) if and only if the link of every vertex is a flag complex. Brady and MacCammond introduced an orthoscheme complex as a generalization of cubical complexes. It is, however, difficult to tell whether an orthoscheme complex is (locally) CAT(0) or not. In this talk, I will discuss a translation of Gromov's characterization for orthoscheme complexes. As a generalization of Gromov's characterization, I will show that the orthoscheme complex of locally distributive semilattice is CAT(0) if and only if it is a flag semilattice.

10月11日 -- 056号室, 17:00 -- 18:30

河澄 響矢 (東京大学大学院数理科学研究科)

The Kashiwara-Vergne problem and the Goldman-Turaev Lie bialgebra in genus zero

Abstract: In view of results of Goldman and Turaev, the free vector space over the free loops on an oriented surface has a natural Lie bialgebra structure. The Goldman bracket has a formal description by using a special (or symplectic) expansion of the fundamental group of the surface. It is natural to ask for a formal description of the Turaev cobracket. We will show how to obtain a formal description of the Goldman-Turaev Lie bialgebra for genus 0 using a solution of the Kashiwara-Vergne problem. A similar description was recently obtained by Massuyeau using the Kontsevich integral. Moreover we propose a generalization of the Kashiwara-Vergne problem in the context of the Goldman-Turaev Lie bialgebra. This talk is based on a joint work with A. Alekseev, Y. Kuno and F. Naef.

10月18日 -- 056号室, 17:30 -- 18:30

橋本 義武 (東京都市大学)


Abstract: This talk is based on a joint work with A. Tsuchiya (Kavli IPMU) and T. Matsumoto (Nagoya Univ). In 2006 Feigin-Gainutdinov-Semikhatov-Tipunin introduced vertex operator algebras M called extended W-algebras. Tsuchiya-Wood developed representation theory of M by the method of "infinitesimal deformation of parameter" and Jack symmetric polynomials.

In this talk I will discuss the following subjects:
1. "factorization" in conformal field theory,
2. tensor structure of the category of M-modules and "module-bimodule correspondence".

11月1日 -- 056号室, 17:00 -- 18:30

大場 貴裕 (東京工業大学)

Higher-dimensional contact manifolds with infinitely many Stein fillings

A Stein fillings of a given contact manifold is a Stein domain whose boundary is contactomorphic to the given contact manifold. Open books, Lefschetz fibrations, and mapping class groups of their fibers in particular help us to produce various contact manifolds and their Stein fillings. However, little is known about mapping class groups of higher-dimensional manifolds. This is one of the reasons that it was unknown whether there is a contact manifold of dimension > 3 with infinitely many Stein fillings. In this talk, I will choose a certain symplectic manifold as fibers of open books and Lefschetz fibrations and by using them, construct an infinite family of higher-dimensional contact manifolds with infinitely many Stein fillings.

11月8日 -- 056号室, 17:00 -- 18:30

秋田 利之 (北海道大学)

Second mod 2 homology of Artin groups

Abstract: After a brief survey on the K(π,1) conjecture and homology of Artin groups, I will introduce our recent result: we determined second mod 2 homology of arbitrary Artin groups without assuming the K(π,1)-conjecture. The key ingredients are Hopf's formula and a result of Howlett on Schur multipliers of Coxeter groups. This is a joint work with Ye Liu.

11月15日 -- 056号室, 17:00 -- 18:30

逆井 卓也 (東京大学大学院数理科学研究科)

Cohomology of the moduli space of graphs and groups of homology cobordisms of surfaces

Abstract: We construct an abelian quotient of the symplectic derivation Lie algebra of the free Lie algebra generated by the fundamental representation of the symplectic group. It gives an alternative proof of the fact first shown by Bartholdi that the top rational homology group of the moduli space of metric graphs of rank 7 is one dimensional. As an application, we construct a non-trivial abelian quotient of the homology cobordism group of a surface of positive genus. This talk is based on joint works with Shigeyuki Morita, Masaaki Suzuki and Gwénaël Massuyeau.

11月22日 -- 056号室, 17:00 -- 18:30

内藤 貴仁 (東京大学大学院数理科学研究科)

Sullivan's coproduct on the reduced loop homology

Abstract: In string topology, Sullivan introduced a coproduct on the reduced loop homology and showed that the homology has an infinitesimal bialgebra structure with respect to the coproduct and Chas-Sullivan loop product. In this talk, I will give a homotopy theoretic description of Sullivan's coproduct. By using the description, we obtain some computational examples of the structure over the rational number field. Moreover, I will also discuss a based loop space version of the coproduct.

11月29日 -- 056号室, 17:30 -- 18:30

千葉 逸人 (九州大学)


Abstract: 一般のグラフの上で定義された大自由度結合振動子系のダイナミクスを考える。 特に、結合強度を大きくしていくと非同期状態から同期状態への相転移が起こることを、 一般化スペクトル理論を用いて示す。

12月6日 -- 056号室, 17:00 -- 18:30

吉田 建一 (東京大学大学院数理科学研究科)

Union of 3-punctured spheres in a hyperbolic 3-manifold

Abstract: An essential 3-punctured sphere in a hyperbolic 3-manifold is isotopic to a totally geodesic one. We will classify the topological types for components of union of the totally geodesic 3-punctured spheres in an orientable hyperbolic 3-manifold. There are special types each of which appears in precisely one manifold.

12月13日 -- 056号室, 17:00 -- 18:30

三松 佳彦 (中央大学)

3 次元多様体上の平面場とそれに接する非圧縮流の漸近的絡み目

Abstract: This is a report on a project in (a very slow) progress which aims to prove the tightness of contact structures associated with algebraic Anosov flows without using Bennequin's nor Gromov's results.
After introducing an interpretation of asymptotic linking pairing in terms of differential forms, we attach a subspaces of exact 2-forms to each plane field. We analyze this space in the case where the plane field is an algebraic Anosov foliation and explain what can be done using results from foliated cohomology and frameworks for secondary characteristic classes. We also show some explicit computations.
To close the talk, a quantization phenomenon which happens when a foliation is deformed into a contact structure is explained and we state some perspectives on applying the results on foliations to the tightness.

12月20日 -- 056号室, 17:00 -- 18:30

Irene Pasquinelli (Durham University)

Deligne-Mostow lattices and cone metrics on the sphere

Abstract: Finding lattices in PU(n,1) has been one of the major challenges of the last decades. One way of constructing lattices is to give a fundamental domain for its action on the complex hyperbolic space.
One approach, successful for some lattices, consists of seeing the complex hyperbolic space as the configuration space of cone metrics on the sphere and of studying the action of some maps exchanging the cone points with same cone angle.
In this talk we will see how this construction of fundamental polyhedra can be extended to almost all Deligne-Mostow lattices with three folding symmetry.