[English]

Tea: 16:30 -- 17:00 コモンルーム

世話係

河野 俊丈

河澄 響矢

北山 貴裕

逆井 卓也

9月26日 [Lie群論・表現論セミナーと合同] -- 056号室, 17:00 -- 18:30

関口 英子 (東京大学大学院数理科学研究科)

Abstract: The classical Penrose transform is generalized to an intertwining operator on Dolbeault cohomologies of complex homogeneous spaces $X$ of (real) semisimple Lie groups.

I plan to discuss a detailed analysis when $X$ is an indefinite Grassmann manifold.

To be more precise, we determine the image of the Penrose transform, from the Dolbeault cohomology group on the indefinite Grassmann manifold consisting of maximally positive $k$-planes in ${\mathbb{C}}^{p,q}$ ($1 \le k \le \min(p,q)$) to the space of holomorphic functions over the bounded symmetric domain.

Furthermore, we prove that there is a duality between Dolbeault cohomology groups in two indefinite Grassmann manifolds, namely, that of positive $k$-planes and that of negative $k$-planes.

10月3日 -- 056号室, 17:00 -- 18:00

Athanase Papadopoulos (IRMA, Université de Strasbourg)

Abstract: I will describe transitions, that is, paths between hyperbolic and spherical geometry, passing through the Euclidean. This is based on joint work with Norbert A’Campo and recent joint work with A’Campo and Yi Huang.

10月10日 -- 056号室, 17:30 -- 18:30

與倉 昭治 (鹿児島大学)

Abstract: A poset-stratified space is a continuous map from a topological space to a poset with the Alexandroff topology. In this talk I will discuss some thoughts about poset-stratified spaces from a naive general-topological viewpoint, some applications such as hyperplane arrangements and poset-stratified space structures of hom-sets, and related topics such as characteristic classes of vector bundles, dependence of maps (by Borsuk) and dependence of cohomology classes (by Thom).

10月17日 -- 056号室, 17:00 -- 18:30

石井 敦 (筑波大学)

Abstract: We introduce augmented Alexander matrices, and construct link invariants. An augmented Alexander matrix is defined with an augmented Alexander pair, which gives an extension of a quandle. This framework gives the twisted Alexander invariant and the quandle cocycle invariant. This is a joint work with Kanako Oshiro.

10月24日 [Lie群論・表現論セミナーと合同] -- 056号室, 17:30 -- 18:30

宮岡 礼子 (東北大学)

Abstract: 球面の等径超曲面のガウス写像による像は，複素２次超曲面Q_n(C)の極小ラグランジュ部分多様体の豊富な例を与える． 簡単な場合，これはQ_n(C)の実形となり，そのフレアホモロジーは既知である． ここでは相異なる主曲率の個数が3,4,6の場合に得られた結果を報告する． 当研究は，入江博（茨城大），Hui Ma（清華大学），大仁田義裕（大阪市大）との共同研究である．

10月31日 -- 056号室, 17:00 -- 18:30

Yash Lodha (École Polytechnique Fédérale de Lausanne)

Abstract: Groups of piecewise projective homeomorphisms provide elegant examples of groups that are non amenable, yet do not contain non abelian free subgroups. In this talk I will present a survey of these groups and discuss their striking properties. I will discuss properties such as (non)amenability, finiteness properties, normal subgroup structure, actions by various degrees of regularity and Tarski numbers.

11月7日 -- 056号室, 17:00 -- 18:30

林 晋 (産総研・東北大オープンイノベーションラボラトリ)

Abstract: In condensed matter physics, topologically protected (codimension-one) edge states are known to appear on the surface of some insulators reflecting some topology of its bulk. Such phenomena can be understood from the point of view of an index theory associated to the Toeplitz extension and are called the bulk-edge correspondence. In this talk, we consider instead the quarter-plane Toeplitz extension and index theory associated with it. As a result, we show that topologically protected (codimension-two) corner states appear reflecting some topology of the gapped bulk and two edges. Such new topological phases can be obtained by taking a ``product’’ of two classically known topological phases (2d type A and 1d type AIII topological phases). By using this construction, we obtain an example of a continuous family of bounded self-adjoint Fredholm quarter-plane Toeplitz operators whose spectral flow is nontrivial, which gives an explicit example of topologically protected corner states.

11月21日 -- 056号室, 17:00 -- 18:30

境 圭一 (信州大学)

Abstract: We prove affirmatively the conjecture raised by J. Mostovoy; the space of short ropes is weakly homotopy equivalent to the classifying space of the topological monoid (or category) of long knots in R^3. We make use of techniques developed by S. Galatius and O. Randal-Williams to construct a manifold space model of the classifying space of the space of long knots, and we give an explicit map from the space of short ropes to the model in a geometric way. This is joint work with Syunji Moriya (Osaka Prefecture University).

11月28日 -- 056号室, 17:00 -- 18:30

Sang-hyun Kim (Seoul National University)

Abstract: Let a>=2 be a real number and k = [a]. We denote by Diff^a(S^1) the group of C^k diffeomorphisms such that the k--th derivatives are Hölder--continuous of exponent (a - k). For each real number a>=2, we prove that there exists a finitely generated group G < Diff^a(S^1) such that G admits no injective homomorphisms into Diff^b(S^1) for any b>a. This is joint work with Thomas Koberda.

12月5日 -- 056号室, 17:00 -- 18:30

川村 一宏 (筑波大学)

Abstract: For a compact metric space M, Lip(M) denotes the Banach algebra of all complex-valued Lipschitz functions on M. Motivated by a classical work of de Leeuw, we define a compact, not necessarily metrizable, Hausdorff space \hat{M} so that each point of \hat{M} induces a derivation on Lip(M). To some extent, \hat{M} may be regarded as "the space of directions." We study, by an elementary method, the space of derivations and continuous Hochschild cohomologies (in the sense of B.E. Johnson and A.Y. Helemskii) of Lip(M) with coefficients C(\hat{M}) and C(M). The results so obtained show that the behavior of Lip(M) is (naturally) rather different than that of the algebra of smooth/C^1 functions on M.

12月12日 -- 056号室, 17:00 -- 18:30

清水 達郎 (京都大学数理解析研究所)

Abstract: 閉 n 次元有向多様体 M から R^p へのMorin写像と呼ばれるクラスの可微分写像の特異点集合は， M の部分多様体をなすことが知られている． この特異点集合の k 重自己交差が定めるホモロジー類と，M から R^{p+k-1} へのgenericな写像の (Jacobianが) k 階退化した特異点集合が定めるホモロジー類が， 2を法として一致することを示す（ただし n>p+k-2）． この事実自体はThom多項式等を用いる方法で間接的に示すことができると思われれるが， 本講演では幾何的な直接の対応を与える． この証明の利点の１つは M が境界を持つ場合に拡張できることである． その応用として3次元多様体の接束の自明化（枠）の不変量である不足符号数と特異点を用いた解釈を与える． ただし，2を法にしている．

12月19日 -- 056号室, 17:30 -- 18:30

宮地 秀樹 (大阪大学)

Abstract: Quadratic differentials are standard and important objects in Teichmuller theory. The deformation space (moduli space) of the quadratic differentials is applied to many fields of mathematics. In this talk, I will develop the deformation of quadratic differentials. Indeed, following pioneer works by A. Douady, J. Hubbard, H. Masur and W. Veech, we describe the infinitesimal deformations in the odd (co)homology groups on the double covering spaces defined from the square roots of the quadratic differentials. We formulate the decomposition theorem for the infinitesimal deformations with keeping in mind of the induced deformation of the moduli of underlying complex structures. As applications, we obtain the Levi form of the Teichmuller distance, and an alternate proof of the Krushkal formula on the pluricomplex Green function on the Teichmuller space.

1月16日 -- 056号室

17:00 -- 18:00

Jimenez Pascual Adrian (東京大学大学院数理科学研究科)

Abstract: It has always been difficult to prove results regarding the (minimal) crossing number of knots. In particular, apparently easy problems such as knowing the crossing number of the connected sum of knots, or bounding the crossing number of satellite knots have been conjectured through decades, yet still remain open. Focusing on this latter problem, in this talk I will prove that the crossing number of a satellite knot is bounded from below by the crossing number of its companion, when the companion is adequate.

18:00 -- 19:00

川島 夢人 (東京大学大学院数理科学研究科)

Abstract: A relation between the dilatation of pseudo-Anosov braids and fixed point theory was studied by Ivanov. In this talk we reveal a new relationship between the above two subjects by showing a formula for the dilatation of pseudo-Anosov braids by means of the representations of braid groups due to B. Jiang and H. Zheng.

1月23日 -- 056号室

17:00 -- 18:00

野崎 雄太 (東京大学大学院数理科学研究科)

Abstract: For a closed 3-manifold X, we consider the topological invariant defined as the minimal integer g such that X is obtained as the closure of a homology cobordism over a surface of genus g. We prove that the invariant equals one for every lens space, which is contrast to the fact that some lens spaces do not admit any open book decomposition whose page is a surface of genus one. The proof is based on the Chebotarev density theorem and binary quadratic forms in number theory.

18:00 -- 19:00

田中 淳波 (東京大学大学院数理科学研究科)

Abstract: Let $S$ be a closed surface of genus $g \geq 2$. The deformation space $AH(S)$ consists of (conjugacy classes of) discrete faithful representations $\rho:\pi_{1}(S) \to PSL_{2}(\mathbb{C})$. McMullen, and Bromberg and Holt showed that $AH(S)$ can self-bump, that is, the interior of $AH(S)$ has the self-intersecting closure. Both of them demonstrated the existence of self-bumping under the exisetence of a non-trivial wrapping projections from an algebraic limits to a geometric limits which wraps an annulus cusp into a torus cusp.

In this talk, given a representation $\rho$ at the boundary of $AH(S)$, we characterize a wrapping projection to a geometric limit associated to $\rho$, by the information of the actions of decomposed Kleinian groups of the image of $\rho$.

1月30日 -- 056号室, 17:00 -- 18:00

池 祐一 (東京大学大学院数理科学研究科)

Abstract: The microlocal sheaf theory due to Kashiwara and Schapira can be regarded as Morse theory with sheaf coefficients. Recently it has been applied to symplectic geometry, after the pioneering work of Tamarkin. In this talk, I will propose a new sheaf-theoretic method to estimate the displacement energy of compact subsets in cotangent bundles. In the course of the proof, we introduce a persistence-like pseudo-distance on Tamarkin's sheaf category. This is a joint work with Tomohiro Asano.

2月21日 (水) 開催日と会場にご注意下さい -- 122号室, 17:00 -- 18:30

Gwénaël Massuyeau (Université de Bourgogne)

Abstract: Habiro introduced the category B of « bottom tangles in handlebodies », which encapsulates the set of knots in the 3-sphere as well as the mapping class groups of 3-dimensional handlebodies. There is a natural filtration on the category B defined using an appropriate generalization of Vassiliev invariants. In this talk, we will show that the completion of B with respect to the Vassiliev filtration is isomorphic to a certain category A which can be defined either in a combinatorial way using « Jacobi diagrams », or by a universal property via the notion of « Casimir Hopf algebra ». Such an isomorphism will be obtained by extending the Kontsevich integral (originally defined as a knot invariant) to a functor Z from B to A. This functor Z can be regarded as a refinement of the TQFT-like functor derived from the LMO invariant and, if time allows, we will evoke the topological interpretation of the « tree-level » of Z. (This is based on joint works with Kazuo Habiro.)

3月30日 (金) 開催日時にご注意下さい -- 056号室

15:00 -- 16:30

Matteo Felder (University of Geneva)

Abstract: The Kashiwara-Vergne Lie algebra krv was introduced by A. Alekseev and C. Torossian. It describes the symmetries of the Kashiwara-Vergne problem in Lie theory. It has been shown to contain the Grothendieck-Teichmüller Lie algebra grt as a Lie subalgebra. Conjecturally, these two Lie algebras are expected to be isomorphic. An important theorem by T. Willwacher states that in degree zero the cohomology of M. Kontsevich's graph complex GC is isomorphic to grt. We will show how T. Willwacher's result induces a natural way to define a nested sequence of Lie subalgebras of krv whose intersection is grt. This infinite family therefore interpolates between the two Lie algebras. For this we will recall several techniques from the theory of graph complexes. If time permits, we will then sketch how one might generalize these notions to establish a "genus one" analogue of T. Willwacher theorem. More precisely, we will define a chain complex whose degree zero cohomology is given by a Lie subalgebra of the elliptic Grothendieck-Teichmüller Lie algebra introduced by B. Enriquez. The last part is joint work in progress with T. Willwacher.

17:00 -- 18:30

Florian Naef (Massachusetts Institute of Technology)

Abstract: Using the intersection and self-intersection of loops on a surface one can define the Goldman-Turaev Lie bialgebra. By earlier joint work with A. Alekseev, N. Kawazumi and Y. Kuno it is known that the linearization problem of the Goldman-Turaev Lie bialgebra is closely related to the Kashiwara-Vergne problem and hence to Drinfeld associators. It turns out that in the case of a genus 0 surface and over the field of complex numbers there is a very direct and explicit proof of the formality of the Goldman-Turaev Lie bialgebra using the monodromy of the Knizhnik-Zamolodchikov connection. This is joint work with Anton Alekseev.

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