アブストラクト事後公開 — 2018年度年会(於:東京大学)
幾何学分科会
特別講演 離散群上のポテンシャル論における距離埋め込みの方法 田中亮吉 (東北大理) We discuss countable groups, mainly focusing on problems related to existence of (bounded) harmonic functions. In particular we study questions such as which group does not admit any nonconstant bounded harmonic function (Liouville property), and when it admits such a function, how all such functions are obtained (Poisson boundary). This problem often requires deep understanding on geometry of underlying groups as well as quantitative behavior of random walks. I will try to present this subject with several explicit key examples, emphasizing on importance of combining different ideas and techniques. msjmeeting2018mar03i001 

特別講演 Seiberg–Witten方程式とその応用 笹平裕史 (九大数理) Since the Seiberg–Witten equations were introduced by Witten in 1994, the equations have produced many significant applications to 3 and 4 dimensional geometry. In this talk, we will discuss some of them and recent progress. msjmeeting2018mar03i002 

特別講演 Toward complex analysis on Teichmüller space 宮地秀樹 (阪大理) In this talk, I will overview the recent progress on my research on the complex analysis on Teichmüller space. The aim of this research is to give a unified treatment between the topological aspect and the complex analytical aspect in Teichmüller theory. I will discuss the infinitesimal deformation of singular Euclidean structures on a surface in aiming for developing the Teichmüller geometry (Extremal length geometry) on Teichmüller space. I also give a formula of the Levi form of the Teichmüller distance and the pluricomplex Green function on the Teichmüller space. If time permits, I will give an idea for unification and a conjecture on the pluricomplex Poisson kernel on the Bers slice. msjmeeting2018mar03i003 

1. 
逆線形平行移動を与える曲線の存在について 永野哲也 (長崎県立大) The existence of the curve to give the inverse linear parallel displacement is not known for a linear parallel displacement of Finsler space generally. A purpose of the study is to establish a mathematical method to find such a curve, but I don’t have it, yet. Today, I report a necessary and sufficient condition for two curves that they are to be such curves to give other inverse linear parallel displacement each other. 

2. 
Construction of symplecticHaantjes manifold of certain Hamiltonian systems 竹内 司 (慶大経済)・細川聖理 (日本医師会ORCA管理機構(株)) SymplecticHaantjes manifolds are constructed for several Hamiltonian systems following Tempesta–Tondo, which yields the complete integrability of systems. 

3. 
Some examples of global Poisson structures on $S^4$ 森山貴之 (三重大教育)・新田貴士 (三重大教育) A Poisson structure is represented by a bivector whose Schouten bracket vanishes. We study a global Poisson structure on $S^4$ associated with a holomorphic Poisson structure on $\mathbb{CP}^3$. The space of the Poisson structures on $S^4$ is a real algebraic variety in the space of holomorphic Poisson structures on $\mathbb{CP}^3$. We generalize it to $\mathbb{HP}^n$ by using the twistor method. Furthermore, we provide examples of Poisson structures on $S^4$ associated with codimension one holomorphic foliations of degree 2 on $\mathbb{CP}^3$. 

4. 
Splitting theorem for sheaves of holomorphic $k$vectors on complex contact manifolds 森山貴之 (三重大教育)・新田貴士 (三重大教育) A complex contact structure $\gamma$ is defined by a system of holomorphic local 1forms satisfying the completely nonintegrability condition. The contact structure induces a subbundle ${\rm Ker}\, \gamma$ of the tangent bundle and a line bundle $L$. In this paper, we prove that the sheaf of holomorphic $k$vectors on a complex contact manifold splits into the sum of $\mathcal{O}(\bigwedge^{k} {\rm Ker}\, \gamma)$ and $\mathcal{O}(L\otimes \bigwedge^{k1} {\rm Ker}\, \gamma)$ as sheaves of $\mathbb{C}$module. The theorem induces the short exact sequence of cohomology of holomorphic $k$vectors, and we obtain vanishing theorems for the cohomology of $\mathcal{O}(\bigwedge^{k}{\rm Ker}\, \gamma)$. 

5. 
Examples of solvmanifolds without LCK structures 澤井 洋 (沼津工高専) Belgun proved that Inoue surface has no Vaisman structures. In this talk, we generalize this result and construct solvmanifolds without LCK structures. Note that these solvmanifolds have LCS structures. 

6. 
Hopf 曲面上に構成される Hermite–Liouville structures について 五十嵐雅之 (東京理大基礎工) In the last 20 years, the Hermite–Liouville structures on compact complex manifolds have been studied. In these studies, almost all of the nonKählerian structures were obtained by deforming from the Kähler–Liouville structure. In this presentation, the speaker will illustrate the construction of the examples of the Hermite–Liouville structure on the Hopf surface, which leads to the complete integrability of its geodesic flow. 

7. 
Hessian of the Ricci Calabi functional 中村 聡 (東北大理) Ricci Calabi functional is a functional on the space of Kähler metrics of a Fano manifold. Its critical points are called generalized Kähler Einstein metrics. In this talk, we show that the Hessian of the Ricci Calabi functional is nonnegative at a generalized Kähler Einstein metric. 

8. 
Remarks on modified Ding functional for toric Fano manifolds 中村 聡 (東北大理) We give a characterization of relative Ding stable toric Fano manifolds in terms of the behavior of the modified Ding functional. We call the corresponding behavior of the modified Ding functional the pseudoboundedness from below. We also discuss the pseudoboundedness of the Ding / Mabuchi functional of general Fano manifolds. 

9. 
Ding汎関数の勾配流とFano多様体の最適退化 久本智之 (名大多元数理) In order to study the optimal degeneration of a Fano manifold, we introduce the Ding flow as the gradient flow of the Ding energy functional on the space of Kahler metrics. 

10. 
粗幾何版アダマール・カルタンの定理について 尾國新一 (愛媛大理) I will talk about one of coarse geometric versions of the socalled Cartan–Hadamard theorem, that is, a coarse Cartan–Hadamard theorem on coarse convex spaces. Also I will deal with coarse homotopy, open cones and the coarse Baum–Connes conjecture. This talk is based on a jointwork with Tomohiro Fukaya (Tokyo Metropolitan University); ‘Tomohiro Fukaya, Shinichi Oguni, A coarse Cartan–Hadamard theorem with application to the coarse Baum–Connes conjecture, preprint, 2017, arXiv:1705.05588’. 

11. 
粗幾何学における非正曲率空間の新しい定式化とその境界 深谷友宏 (首都大東京理工) In the joint work with Shinichi Oguni, we introduced a new class of metric spaces which we call “coarsely convex spaces”. This is a new formulation of “nonpositively curved spaces” from the view point of coarse geometry. This class includes Gromov hyperbolic spaces, CAT(0)spaces, and systolic complexes. This class is closed under quasiisometry, and direct product. The idea of the definition is “convexity of metric” and its coarsification. We also construct an ideal boundary for coarsely convex spaces. The construction is based on that of Gromov hyperbolic spaces. Due to time constraints, in this talk, we will not explain on an application to the coarse Baum–Connes conjecture, which is the original motivation of this work. 

12. 
Gromovの$\mathrm{Cycl}_k (0)$条件の一般化と$\mathrm{CAT}(0)$空間の5点部分集合の内在的特徴付け 豊田 哲 (鈴鹿工高専) In this talk, we present the result that the $\mathrm{Cycl}_4 (0)$ condition implies the $\mathrm{Cycl}_k (0)$ condition for any integer $k\geq 4$. We also present the result that a fivepoint metric space embeds isometrically into a $\mathrm{CAT}(0)$ space if and only if it satisfies the $\boxtimes$inequalities. 

13. 
エネルギー汎関数の収束と曲率次元条件の安定性のための新しい条件 数川大輔 (東北大理) Gigli, Mondino, and Savaré introduced the pmGconvergence on the space of pointed metric measure spaces and studied the stability of the curvaturedimension condition and the Mosco convergence of Cheeger energies under the pmGconvergence. We introduce a new condition generalizing the pmGconvergence and then prove similar results under this condition. Our study is also related to the study by García, Kell, Mondino, and Sosa for quotient spaces by actions of compact groups. 

14. 
Isoperimetric rigidity and distributions of 1Lipschitz functions 中島啓貴 (東北大理)・塩谷 隆 (東北大理) We prove that if a geodesic metric measure space satisfies a comparison condition for the isoperimetric profile and if the observable variance is maximal, then the space is foliated by minimal geodesics, where the observable variance is defined to be the supremum of the variance of 1Lipschitz functions on the space. Our result can be considered as a variant of Cheeger–Gromall’s splitting theorem and also of Cheng’s maximal diameter theorem. As an application, we obtain an isometric splitting theorem for a complete weighted Riemannian manifold with positive Bakry–Émery Ricci curvature. 

15. 
Lipschitz order with an additive error and normal law à la Lévy on the Hamming cubes 中島啓貴 (東北大理) M. Gromov introduced the Lipschitz order relation on the set of metric measure spaces and developed a rich theory. For a metric measure space $X$, we consider the set of the distributions of 1Lipschitz functions on $X$ and we call it the 1measurement of $X$. We also define Lipschitz order on the 1measurement naturally. The existence of the maximum of 1measurement is deeply related to the isoperimetric inequality of $X$. In fact if $X$ is an $n$dimensional sphere, we obtain the maximum of 1measurement by the isoperimetric inequality. However, if $X$ is a $n$dimensional Hamming cube, the maximum of 1measurement does not exist because of discreteness. We solve this problem by generalizing the definition of Lipschitz order with an error. On the spheres case, we have Normal law à la Lévy by considering the weak limit. We have the Hamming cubes version of it as an application of the main theorem. 

16. 
The Ricci curvature and the Laplacian on edges of graphs 山田大貴 (東北大理)・J. Jost (Max Planck Inst.) We define the distance between edges of graphs and study the coarse Ricci curvature on edges. We consider the Laplacian on edges based on the definition of the Laplacian on simplicial complexes. As one of our main results, we obtain an estimate of the first nonzero eigenvalue of the Laplacian by the Ricci curvature for a regular graph. 

17. 
アレクサンドロフ空間の鈍角定数と体積 三石史人 (福岡大理)・山口孝男 (京大理) We introduce a new geometric invariant called the obtuse constant of spaces with curvature bounded below, defined in terms of comparison angles. We first find relations between this invariant and volume. We discuss the case of maximal obtuse constant equal to $\pi/2$, where we prove some rigidity for spaces. Although we consider Alexandrov spaces with curvature bounded below, the results are new even in the Riemannian case. 

18. 
共点, 共線の定理の発見 蛭子井博孝 (幾何数学研究センター) In the history, there are several elementary theorems by figure. We try to find such theorems, and found new 6 theorems. We show entire structures in figures of our text. We explain briefly them by naming as (1) starstar theorem (2) quadrangle Stainer theorem (3) 6 perpendicularlines theorem (these 3 are concurrent theorems), (4) 10 lines theorem (5) 2 circles system theorem (6) Hexagon Theorem (these 3 are Collinear theorems). These are not proved. But, these theorems include important theoretical structures, and, it is interesting to follow the drawing orders and to consider on the compositions. Anyway, we show all figures of Theorems in our text. Please enjoy many strangeness of theorems. We will be able to speak some relations of theorems in later. 

19. 
$\mathbb{R}^n$の部分多様体の留数と内在的体積 今井 淳 (千葉大理) We show that the intrinsic volumes of compact bodies in the Euclidean spaces of dimension two and three can be obtained from the residues of the (relative) Brylinski beta functions. 

20. 
Delzant多面体のモジュライ空間上の距離関数の構成 大橋佳歩 (日本女大理) A. Pelayo–A. R. Pires–T. S. Ratiu–S. Sabatini defined a metric on the set of Delzant polytopes. They studied structures of the metric space and the moduli space with respect to the action of the integral affine transformations. The definition of the metric is natural, though, it does not induce a metric on the moduli space. In this talk we would like to try to define a metric on the moduli space. We can show that it actually defines a metric on the moduli space for 2dimensional case. 

21. 
双曲空間の単体の垂心の存在 佐藤健治 (玉川大工) We consider orthocenters of simplices of hyperbolic spaces. Unlike the cases of Euclidean spaces or spheres, the similar condition does not always imply the existence of orthocenters. In this talk, we give characterizations of the existence of orthocenters. 

22. 
左不変計量のmoduli空間の特異点及び対応する計量の性質について 武富雄一郎 (広島大理) The moduli space of leftinvariant metrics on a Lie group is defined as the orbit space of the action of the group of automorphisms and scalings on the space of leftinvariant metrics, and has been studied actively. In this talk, we focus on some kinds of singular points which arise in the moduli space. We show that if an equivalent class of a leftinvariant metric is the “most singular” point in the moduli space, then the leftinvariant metric has nice properties. 

23. 
Knots and links of complex tangents 粕谷直彦 (京都産大理)・高瀬将道 (成蹊大理工) We show that a link in a closed orietable 3manifold can be realized as the set of complex tangents of a smooth embedding of the 3manifold into the complex 3space if and only if it represents the trivial integral homology class in the 3manifold. 

24. 
トーラス上の測地円の漸近挙動 印南信宏 (新潟大理) We prove that in any 2torus $T^2$ for any point $p \in T^2$ and for any $\varepsilon > 0$ there exists a number $R > 0$ such that the geodesic circles with center $p$ and radii $t$ are $\varepsilon$dense in $T^2$ for all $t > R$. 

25. 
Hopfのピンチング予想から微分異種球面定理へ 近藤 慶 (山口大理) We prove that for an arbitrarily given compact Riemannian manifold $M$ admitting a point $p \in M$ with a single cut point, every compact Riemannian manifold $N$ admitting a point $q \in N$ with a single cut point is diffeomorphic to $M$ if the radial curvature of $N$ at $q$ are sufficiently close in the sense of $L^1$norm to that of $M$ at $p$. 

26. 
ラプラシアンの第1固有値を最大化する種数2閉曲面上の計量 庄田敏宏 (佐賀大教育)・納谷 信 (名大多元数理) We will consider the upper bound for the first eigenvalue of the Laplacian on a closed surface. For the genus two case, we obtain a singular metric which maximize the first eigenvalue. This result was conjectured by Jakobson–Levitin–Nadirashvili–Nigam–Polterovich. It is joint work with Shin Nayatani, Nagoya University. 

27. 
Realizations of some contact metric manifolds as Ricci soliton real hypersurfaces Jong Taek Cho (Chonnam Nat. Univ.)・橋永貴弘 (北九州工高専)・久保 亮 (広島修道大経済)・武富雄一郎 (広島大理)・田丸博士 (広島大理) Ghosh and Sharma have studied $(\kappa,\mu)$spaces, which are contact metric spaces with certain nullity conditions. Especially, they gave a necessary condition for $(\kappa,\mu)$spaces to be nongradient Ricci soliton manifolds. In this talk, we prove that in the connected, simplyconnected and complete case such $(\kappa,\mu)$spaces can be realized as homogeneous real hypersurfaces in noncompact real twoplane Grassmannians. Consequently, we also prove that such spaces are actually Ricci soliton. % via submanifold theory. 

28. 
トーラス上のホモロジー的ミラー対称性に関するいくつかの注意点 小林和志 (千葉大理) Let us consider an $n$dimensional complex torus whose period matrix is $(I_n,T)$. Here, $I_n$ is the identity matrix of order $n$ and $T$ is a complex matrix of order $n$ whose imaginary part is positive definite. In particular, when we consider the case of $n=1$, i.e., a onedimensional complex torus, the corresponding complexified symplectic form of the mirror partner of the onedimensional complex torus is defined by $\frac{1}{T}$ or $T$. However, if we assume $n \geq 2$ and that $T$ is a singular matrix, we can not define the mirror partner of the complex torus as the natural generalization of the case of $n=1$ to the higher dimensional case. In this talk, we propose a way to avoid this problem, and discuss the homological mirror symmetry. 

29. 
超幾何型調和多様体と球Fourier変換論 伊藤光弘 (筑波大数理物質)・佐藤弘康 (日本工大工) We define a class of harmonic Hadamard manifolds of hypergeometric type. This class of harmonic manifolds includes all Damek–Ricci spaces and also all rank one symmetric spaces of noncompact type as particular cases. Using a hypergeometric description of spherical functions on each harmonic Hadamard manifold $X$ belonging to this class, we discuss harmonic analysis of radial functions on $X$. In this talk we would like to present the inversion formula, Plancherel theorem and Paley–Wiener type theorem for the spherical Fourier transform on a Hadamard harmonic manifold which is of hypergeometric type. 

30. 
楕円軌道上の等質正則直線束にまつわる実半単純リー群の既約ユニタリ表現 坊向伸隆 (大分大理工) In this talk I consider a homogeneous holomorphic line bundle over a certain elliptic (adjoint) orbit, and set a representation of real semisimple Lie group on a complex vector subspace of the complex vector space of holomorphic crosssections of the bundle. Then, I state that the representation is irreducible unitary. 

31. 
Fibered cusp $b$pseudodifferential operators and its applications 渡部 淳 (東大数理) Let $X$ be a smooth compact manifold with corners which has two embedded boundary hypersurfaces $\partial _0 X , \partial _1 X$, and suppose a fiber bundle $\phi: \partial_0 X \to Y $ is given. We define a pseudodifferential calculus $\Psi^*_{\Phi,b}(X)$ generalizing the $\Phi$calculus of Mazzeo–Melrose and the $b$calculus of Melrose. We investigate the Fredholm condition and the index of an operator $P \in \Psi^*_{\Phi,b}(X)$. And as its application, we prove the index theorem of “nonclosed” $\mathbb{Z}/k$manifolds. 

32. 
Riemann 多様体上の弾性曲線の波動運動方程式 小磯憲史 (九大IMI／阪大名誉教授) A wave equation of motion of an elastic wire on a Riemannian manifold has a solution for any initial data. 

33. 
重み付きハミルトン安定性と変形ラグランジュ平均曲率流 梶ヶ谷徹 (MathAMOIL)・國川慶太 (東北大AIMR) We generalize several results for the Hamiltonian stability and the mean curvature flow of Lagrangian submanifolds in a Kähler–Einstein manifold to more general Kähler manifolds including a Fano manifold equipped with a Kähler form $\omega\in 2\pi c_1(M)$. Namely, we consider a variational problem for Lagrangian submanifolds in a Kähler manifold $M$ w.r.t. a weighted volume functional. Moreover, we introduce the generalized Lagrangian mean curvature flow in a Fano manifold, and we show that if the initial Lagrangian is a small Hamiltonian deformation of a minimal and Hamiltonian stable Lagrangian w.r.t. the weighted volume functional, then the generalized MCF converges exponentially fast to a minimal Lagrangian submanifold. 

34. 
特異点を持つ非等方的平均曲率一定閉超曲面の非一意性と非等方的平均曲率流方程式への応用 小磯深幸 (九大IMI) An anisotropic surface energy is a generalizasion of the area of surfaces. It is the integral of an energy density function which depends on the surface normal over the considered surface, and it serves as a mathematical model of energy of crystals. The absolute minimizer of an anisotropic surface energy functional among all closed surfaces enclosing the same volume is unique and it is called the Wulff shape. In this talk, we show that, if the energy density function is not “convex”, there exist closed equilibrium surfaces of the anisotropic surface energy for volumepreserving variations which are not the Wulff shape. By applying this result, it is shown that the uniqueness for closed selfsimilar solutions with genus zero for anisotropic mean curvature flow does not hold in general. These concepts and results are naturally generalized to higher dimensions. 

35. 
特異点を持つ安定な非等方的平均曲率一定閉超曲面の一意性 小磯深幸 (九大IMI) An anisotropic surface energy is a generalizasion of the area of surfaces. It is the integral of an energy density function which depends on the surface normal over the considered surface, and it serves as a mathematical model of energy of crystals. The absolute minimizer of an anisotropic surface energy functional among all closed surfaces enclosing the same volume is unique and it is called the Wulff shape. In this talk, we show that, if the energy density function is of $C^3$ and “convex”, then any stable closed equilibrium surface of the anisotropic surface energy for volumepreserving variations is (up to homothety and translation) the Wulff shape, here an equilibrium surface is said to be stable if the second variation of the energy for all admissible variations is nonnegative. The result holds also for hypersurfaces in any Euclidean space. 

36. 
5次元空間形の極小曲面の変換 榊 真 (弘前大理工) We discuss transforms for minimal surfaces in 5dimensional Riemannian space forms, and Lorentzian minimal surfaces in the 5dimensional semiEuclidean space of index 2. 

37. 
3次元ユークリッド空間の非共形調和曲面の変換と表現公式 榊 真 (弘前大理工) We give transforms and a representation formula for nonconformal harmonic surfaces in the Euclidean 3space. 

38. 
キャリブレーション等式と超極作用 馬場蔵人 (東京理大理工)・井川 治 (京都工繊大工芸)・笹木集夢 (東海大理) In this talk, we give a proof for calibrated equalities from the viewpoint of group actions. The essential part of our proof is to describe the orbit spaces for certain group actions on oriented Grassmann manifolds. 

39. 
擬リーマン幾何学におけるキャリブレーション不等式と双対性 馬場蔵人 (東京理大理工)・井川 治 (京都工繊大工芸)・笹木集夢 (東海大理) In this talk, we give a proof for Mealy’s calibrated inequalities from the view point of group actions. As a typical example, we prove Wirtinger’s inequality in terms of the duality which was introduced by the speakers. 

40. 
混合型曲面の等長変形 本田淳史 (横浜国大工) For a regular surface in Lorentz–Minkowski 3space, a point is called a lightlike point if the first fundamental form is degenerate at the point. In this talk, we prove that any analytic surface admits nontrivial isometric deformations around a nonflat and nondegenerate lightlike point. 

41. 
Classification of Cartan embeddings which are austere submanifolds 木村太郎 (鶴岡工高専)・間下克哉 (法政大理工) In this talk, we will classify austere submanifolds in compact simple Lie groups. In particular, we proved that Cartan embeddings which defined by inner automorphisms of finite order $k >2$ of compact simple Lie gruops are not austere. 

42. 
複素旗多様体内の二つの実形のFloerホモロジー 井川 治 (京都工繊大工芸)・入江 博 (茨城大理)・奥田隆幸 (広島大理)・酒井高司 (首都大東京理工)・田崎博之 (筑波大数理物質) An adjoint orbit $M$ of a compact connected semisimple Lie group $G$ is called a complex flag manifold. The intersection of two real forms $L_0$ and $L_1$ in a complex flag manifold $M$ is an antipodal set of $M$. Applying the antipodal structure of the intersection $L_0 \cap L_1$, we calculate the Lagrangian Floer homology $HF(L_0, L_1 : {\mathbb Z}_2)$, when $M$ has a $G$invariant Kähler–Einstein metric and when two involutions of $G$ defining $L_0$ and $L_1$ commute with each other. 

43. 
Construction of pseudoAnosov automorphisms whose dilatations are 2Salem numbers 小森洋平 (早大教育) We construct a pseudoAnosov automorphism whose dilatation is a 2Salem number by means of the spectrum radius of the bicolored Coxeter element of a bipartite Coxeter system. 