Seminar on Geometric Complex Analysis

Seminar information archive ~12/02Next seminarFuture seminars 12/03~

Date, time & place Monday 10:30 - 12:00 128Room #128 (Graduate School of Math. Sci. Bldg.)
Organizer(s) Kengo Hirachi, Shigeharu Takayama, Ryosuke Nomura

Seminar information archive

2021/11/29

10:30-12:00   Online
Akira Kitaoka (The University of Tokyo)
レンズ空間上のRay-Singer捩率とRumin複体のラプラシアン (Japanese)
[ Abstract ]
Rumin複体は、接触多様体に関するBernstein-Gelfand-Gelfand複体(BGG複体)である。BGG複体は、放物型幾何やフィルター付き多様体に対して構成される複体であり、BGG複体のコホモロジーはde Rhamコホモロジーに一致するという事が挙げられる。また、Rumin複体はsub-Riemmann極限を考えた際に自然に現れるという性質を持つ。

De Rham複体を使って定義した概念をRumin複体に置き換えるとどうなるのか、ということを考える。本講演では、この考えを解析的捩率に適応した場合を話す。レンズ空間上のユニモジュラーなホロのミーから誘導される平坦ベクトル束に対して、Rumin複体の解析的捩率の値が、Betti数とRay-Singer捩率を用いて表されることを報告する。
[ Reference URL ]
https://u-tokyo-ac-jp.zoom.us/meeting/register/tJ0vcu2rrDIqG9Rv5AT0Mpi37urIkJ1IRldB

2021/11/15

10:30-12:00   Online
Katsusuke Nabeshima (Tokyo University of Science)
Computing logarithmic vector fields along an isolated singularity and Bruce-Roberts Milnor ideals (Japanese)
[ Abstract ]
The concept of logarithmic vector fields along a hypersurface, introduced by K. Saito (1980), is of considerable importance in singularity theory.
Logarithmic vector fields have been extensively studied and utilized by several researchers. A. G. Aleksandrov (1986) and J. Wahl (1983) considered quasihomogeneous complete intersection cases and gave independently, among other things, a closed formula of generators of logarithmic vector fields. However, there is no closed formula for generators of logarithmic vector fields, even for semi-quasihomogeneous hypersurface isolated singularity cases. Many problems related with logarithmic vector fields remain still unsolved, especially for non-quasihomogeneous cases.
Bruce-Roberts Milnor number was introduced in 1988 by J. W. Bruce and R. M. Roberts as a generalization of the Milnor number, a multiplicity of an isolated critical point of a holomorphic function germ. This number is defined for a critical point of a holomorphic function on a singular variety in terms of logarithmic vector fields. Recently, Bruce-Robert Milnor numbers are investigated by several researchers. However, many problems related with Bruce-Roberts Milnor numbers remain unsolved.
In this talk, we consider logarithmic vector fields along a hypersurface with an isolated singularity. We present methods to study complex analytic properties of logarithmic vector fields and illustrate an algorithm for computing logarithmic vector fields. As an application of logarithmic vector fields, we consider Bruce-Roberts Milnor numbers in the context of symbolic computation.
[ Reference URL ]
https://u-tokyo-ac-jp.zoom.us/meeting/register/tJ0vcu2rrDIqG9Rv5AT0Mpi37urIkJ1IRldB

2021/10/11

10:30-12:00   Online
Takahiro Aoi (Abuno High School)
cscK計量に付随する完備スカラー平坦Kähler計量について (Japanese)
[ Abstract ]
複素多様体上のKähler計量であって, そのスカラー曲率が定数となるもの(cscK計量)が存在するか, という問題は非自明であり,極めて重要である.ここでは正則ベクトル場などに対して適当な条件を満たす偏極多様体と, 滑らかな超曲面を考える. 本講演では,この超曲面を無限遠と見做し, それが適当な偏極類にcscK計量を持つ, という境界条件を満たせば,その補集合は漸近錐的完備なスカラー平坦Kähler計量を許容する, という結果について紹介を行い,時間が許す限り関連する問題についても紹介する.
[ Reference URL ]
https://u-tokyo-ac-jp.zoom.us/meeting/register/tJ0vcu2rrDIqG9Rv5AT0Mpi37urIkJ1IRldB

2021/07/19

10:30-12:00   Online
Makoto Abe (Hiroshima University)
$\mathbb{C}^n$上の不分岐Riemann領域に対する中間的擬凸性 (Japanese)
[ Abstract ]
The talk is based on a joint work with T. Shima and S. Sugiyama.
We characterize the intermediate pseudoconvexity for unramified Riemann domains over $\mathbb{C}^n$ by the continuity property which holds for a class of maps whose projections to $\mathbb{C}^n$ are families of unidirectionally parameterized intermediate dimensional analytic balls written by polynomials of degree $\le 2$.
[ Reference URL ]
https://u-tokyo-ac-jp.zoom.us/meeting/register/tJ0vcu2rrDIqG9Rv5AT0Mpi37urIkJ1IRldB

2021/07/12

10:30-12:00   Online
Katsuhiko Matsuzaki (Waseda University)
Parametrization of Weil-Petersson curves on the plane (Japanese)
[ Abstract ]
A Weil-Petersson curve is the image of the real line by a quasiconformal homeomorphism of the plane whose complex dilatation is square integrable with respect to the hyperbolic metrics on the upper and the lower half-planes. We consider two parameter spaces of all such curves and show that they are biholomorphically equivalent. As a consequence, we prove that the variant of the Beurling-Ahlfors quasiconformal extension defined by using the heat kernel for the convolution yields a global real-analytic section for the Teichmueller projection to the Weil-Petersson Teichmueller space. This is a joint work with Huaying Wei.
[ Reference URL ]
https://u-tokyo-ac-jp.zoom.us/meeting/register/tJ0vcu2rrDIqG9Rv5AT0Mpi37urIkJ1IRldB

2021/07/05

10:30-12:00   Online
Nitta Yasufumi (Tokyo University of Science)
Several stronger concepts of relative K-stability for polarized toric manifolds (Japanese)
[ Abstract ]
We study relations between algebro-geometric stabilities for polarized toric manifolds. In this talk, we introduce several strengthenings of relative K-stability such as uniform stability and K-stability tested by more objects than test configurations, and show that these approaches are all equivalent. As a consequence, we solve a uniform version of the Yau-Tian-Donaldson conjecture for Calabi's extremal Kähler metrics in the toric setting. This talk is based on a joint work with Shunsuke Saito.
[ Reference URL ]
https://u-tokyo-ac-jp.zoom.us/meeting/register/tJ0vcu2rrDIqG9Rv5AT0Mpi37urIkJ1IRldB

2021/06/28

10:30-12:00   Online
Yûsuke Okuyama (Kyoto Institute of Technology)
Orevkov's theorem, Bézout's theorem, and the converse of Brolin's theorem (Japanese)
[ Abstract ]
The converse of Brolin's theorem was a problem on characterizing polynomials among rational functions (on the complex projective line) in terms of the equilibrium measures canonically associated to rational functions. We would talk about a history on the studies of this problem, its optimal solution, and a proof outline. The proof is reduced to Bézout's theorem from algebraic geometry, thanks to Orevkov's irreducibility theorem on polynomial lemniscates. This talk is based on joint works with Małgorzata Stawiska (Mathematical Reviews).
[ Reference URL ]
https://u-tokyo-ac-jp.zoom.us/meeting/register/tJ0vcu2rrDIqG9Rv5AT0Mpi37urIkJ1IRldB

2021/06/14

10:30-12:00   Online
Takayuki Koike (Osaka City University)
Projective K3 surfaces containing Levi-flat hypersurfaces (Japanese)
[ Abstract ]
In May 2017, I reported on the gluing construction of a K3 surface at Seminar on Geometric Complex Analysis.
Here, by the gluing construction of a K3 surface, I mean the construction of a K3 surface by holomorphically gluing two open complex surfaces which are the complements of tubular neighborhoods of elliptic curves included in the blow-ups of the projective planes by nine points.
As of 2017, it was an open problem whether a projective K3 surface can be obtained by the gluing construction. Recently, I and Takato Uehara found a very concrete way to construct a projective K3 surface by the gluing method. As a corollary, we obtained the existence of non-Kummer projective K3 surface with compact Levi-flat hypersurfaces.
In this talk, I will explain the detail of the concrete gluing construction of such a K3 surface.
[ Reference URL ]
https://u-tokyo-ac-jp.zoom.us/meeting/register/tJ0vcu2rrDIqG9Rv5AT0Mpi37urIkJ1IRldB

2021/06/07

10:30-12:00   Online
Kurando Baba (Tokyo University of Science)
Calabi-Yau structure and Bargmann type transformation on the Cayley projective plane (Japanese)
[ Abstract ]
In this talk, I would like to discuss a problem of the geometric quantization for the Cayley projective plane. Our purposes are to show the existence of a Calabi-Yau structure on the punctured cotangent bundle of the Cayley projective plane, and to construct a Bargmann type transformation between a space of holomorphic functions on the bundle and the $L_2$-space on the Cayley projective space. The transformation gives a quantization of the geodesic flow in terms of one parameter group of elliptic Fourier integral operators. This talk is based on a joint work with Kenro Furutani (Osaka City University Advanced Mathematical Institute): arXiv:2101.07505.
[ Reference URL ]
https://u-tokyo-ac-jp.zoom.us/meeting/register/tJ0vcu2rrDIqG9Rv5AT0Mpi37urIkJ1IRldB

2021/05/31

10:30-12:00   Online
Yuya Takeuchi (Tsukuba University)
Nonnegativity of the CR Paneitz operator for embeddable CR manifolds (Japanese)
[ Abstract ]
The CR Paneitz operator, which is a fourth-order CR invariant differential operator, plays a crucial role in three-dimensional CR geometry; it is deeply connected to global embeddability and the CR positive mass theorem. In this talk, I will show that the CR Paneitz operator is nonnegative for embeddable CR manifolds. I will also apply this result to some problems in CR geometry. In particular, I will give an affirmative solution to the CR Yamabe problem for embeddable CR manifolds.
[ Reference URL ]
https://u-tokyo-ac-jp.zoom.us/meeting/register/tJ0vcu2rrDIqG9Rv5AT0Mpi37urIkJ1IRldB

2021/05/24

10:30-12:00   Online
Atsushi Hayashimoto (Nagano National College of Technology)
Cartan-Hartogs領域の固有正則写像 (Japanese)
[ Abstract ]
2つの球の間の固有正則写像は自己同型写像である。球を別の領域にしたらどうなるかを調べたい。球の一般化として複素擬楕円体や有界対称領域が考えられる。これら2つの領域を合わせた領域としてHua領域がある。これは有界対称領域の上に複素擬楕円体が乗っているような領域である。Hua領域の一番簡単な場合としてCartan-Hartogs領域があり、これらの間の固有正則写像の分類問題を考える。分類すると本質的には1種類の写像しかないことが分かる。ここでは2つの多項式写像が自己同型写像の差を省いて一致すれば、Isotoropy写像の差を省いて一致することを使う。
[ Reference URL ]
https://u-tokyo-ac-jp.zoom.us/meeting/register/tJ0vcu2rrDIqG9Rv5AT0Mpi37urIkJ1IRldB

2021/05/10

10:30-12:00   Online
Naohiko Kasuya (Hokkaido University)
強擬凹複素曲面の境界に現れる接触構造 (Japanese)
[ Abstract ]
強擬凸複素曲面の境界は3次元強擬凸CR多様体であり、正の接触構造を誘導する。BogomolovとDe Oliveiraは強擬凸複素曲面の境界に現れる接触構造はStein fillableであること(CR構造としては、Stein fillableなものに変形同値であること)を示した。

一方、強擬凹複素曲面の境界には負の3次元接触構造が現れる。本講演では、任意の負の3次元閉接触多様体が強擬凹複素曲面の境界として実現可能であることを示す。証明は、EliashbergによるStein manifoldの構成法を参考にして強擬凹境界への正則ハンドルの接着手法を確立することによってなされる。

尚、本講演内容はDaniele Zuddas氏(トリエステ大学)との共同研究である。
[ Reference URL ]
https://u-tokyo-ac-jp.zoom.us/meeting/register/tJ0vcu2rrDIqG9Rv5AT0Mpi37urIkJ1IRldB

2021/04/26

10:30-12:00   Online
Jun O'Hara (Chiba University)
多様体の留数 (Japanese)
[ Abstract ]
$M$を多様体、$z$を複素数とし、$M$の二点間の距離の$z$乗を積空間$M\times M$上積分したものを考えると、$z$の実部が大きいところで$z$の正則関数になる。解析接続により複素平面上の有理関数で1位の極のみ持つものが得られる。この有理型関数、特にその留数の性質を紹介する。具体的には、メビウス不変性、留数と似た量(曲面のWillmoreエネルギー、4次元多様体のGraham-Wittenエネルギー、積分幾何で出てくる内在的体積、ラプラシアンのスペクトルなど)との比較、有理型関数・留数による多様体の同定問題などを扱う。
参考資料:https://sites.google.com/site/junohara/ ダウンロード 「多様体のエネルギーと留数」(少し古い), arXiv:2012.01713
[ Reference URL ]
https://u-tokyo-ac-jp.zoom.us/meeting/register/tJ0vcu2rrDIqG9Rv5AT0Mpi37urIkJ1IRldB

2021/04/19

10:30-12:00   Online
Shouhei Ma (Tokyo Institute of Technology)
カスプと有理同値 (Japanese)
[ Abstract ]
標題の「カスプ」とはいわゆるモジュラー多様体の(ベイリー・ボレル)コンパクト化の境界成分のことである。
1970年代にマニンとドリンフェルトは合同モジュラー曲線の2つのカスプの差がピカール群において有限位数であることを発見した。
代数サイクルの観点からこの現象の高次元版をいくつか古典的な系列のモジュラー多様体の(ベイリー・ボレル、トロイダル)コンパクト化に対して調べたので、それについて報告する。
[ Reference URL ]
https://u-tokyo-ac-jp.zoom.us/meeting/register/tJ0vcu2rrDIqG9Rv5AT0Mpi37urIkJ1IRldB

2021/01/25

10:30-12:00   Online
Young-Jun Choi (Pusan National University)
Existence of a complete holomorphic vector field via the Kähler-Einstein metric
[ Abstract ]
A fundamental problem in Several Complex Variables is to classify bounded pseudoconvex domains in the complex Euclidean space with a noncompact automorphism group, especially with a compact quotient. In the results of Wong-Rosay and Frankel, they make use of the "Scaling method'' for obtaining an 1-parameter family of automorphisms, which generates a holomorphic vector field.
In this talk, we discuss the existence of a nowhere vanishing complete holomorphic vector filed on a strongly pseudoconvex manifold admtting a negatively curved Kähler-Einstein metric and discrete sequence of automorphisms by introducing the scaling method on potentials of the Kähler-Einstein metric.
[ Reference URL ]
https://zoom.us/meeting/register/tJ0vcu2rrDIqG9Rv5AT0Mpi37urIkJ1IRldB

2021/01/18

10:30-12:00   Online
HAMANO Sachiko (Osaka City University)
The hydrodynamic period matrices and closings of an open Riemann surface of finite genus
[ Abstract ]
A closing of an open Riemann srface $R$ of finite genus is a shorter name of a closed Riemann surface of the same genus into which $R$ can be embedded by a homology type preserving conformal mapping. We observe the Riemann period matrices of all closings of $R$ in the Siegel upper half space. It is known that every hydrodynamic differential on $R$ yields a closing of $R$ called a hydrodynamic closing. (A hydrodynamic differential is a holomorphic which describes a steady flow on $R$ of an ideal fluid.) We study the period matices induced by hydrodynamic closings of $R$. This is a joint work with Masakazu Shiba.
[ Reference URL ]
https://zoom.us/meeting/register/tJ0vcu2rrDIqG9Rv5AT0Mpi37urIkJ1IRldB

2020/12/21

10:30-12:00   Online
Martin Sera (KUAS)
On a mixed Monge-Ampère operator for quasiplurisubharmonic functions
[ Abstract ]
This reports on a joint work with R. Lärkäng and E. Wulcan. We consider mixed Monge-Ampère products of quasiplurisubharmonic functions with analytic singularities (introduced in a previous work with H. Raufi additionally). These products have the advantage that they preserve mass (a property which is missing for non-pluripolar products).
The main result of the work presented here is that such Monge-Ampère products can be regularized as explicit one parameter limits of mixed Monge-Ampère products of smooth functions, generalizing a result of Andersson-Błocki-Wulcan. We will explain how the theory of residue currents, going back to Coleff-Herrera, Passare and others, plays an important role in the proof.
As a consequence, we get an approximation of Chern and Segre currents of certain singular hermitian metrics on vector bundles by smooth forms in the corresponding Chern and Segre classes.
[ Reference URL ]
https://zoom.us/meeting/register/tJ0vcu2rrDIqG9Rv5AT0Mpi37urIkJ1IRldB

2020/12/14

10:30-12:00   Online
ADACHI Masanori (Shizuoka University)
On Levi flat hypersurfaces with transversely affine foliation
[ Abstract ]
In this talk, we discuss the classification problem of Levi flat hypersurfaces in complex surfaces by restricting ourselves to the case that the Levi foliation is transversely affine. After presenting known examples, we give a proof for the non-existence of real analytic Levi flat hypersurface whose complement is 1-convex and Levi foliation is transversely affine in a compact Kähler surface. This is a joint work with Severine Biard (arXiv:2011.06379).
[ Reference URL ]
https://zoom.us/meeting/register/tJ0vcu2rrDIqG9Rv5AT0Mpi37urIkJ1IRldB

2020/11/30

10:30-12:00   Online
IWAI Masataka (Osaka City Univ. and Kyoto Univ.)
On asymptotic base loci of relative anti-canonical divisors
[ Reference URL ]
https://zoom.us/meeting/register/tJ0vcu2rrDIqG9Rv5AT0Mpi37urIkJ1IRldB

2020/11/09

10:30-12:00   Online
NOSE Toshihiro (Fukuoka Institute of Technology)
Meromorphic continuation of local zeta functions and nonpolar singularities
[ Reference URL ]
https://zoom.us/meeting/register/tJ0vcu2rrDIqG9Rv5AT0Mpi37urIkJ1IRldB

2020/10/26

10:30-12:00   Online
HATTORI Kota (Keio University)
Spectral convergence in geometric quantization
[ Reference URL ]
https://zoom.us/meeting/register/tJ0vcu2rrDIqG9Rv5AT0Mpi37urIkJ1IRldB

2020/10/19

10:30-12:00   Online
MATSUMURA, Shin-ichi (Tohoku University)
On projective manifolds with pseudo-effective tangent bundle
[ Abstract ]
In this talk, I would like to discuss projective manifolds whose tangent bundle is pseudo-effective or admits a positively curved singular metric. I will explain a structure theorem for such manifolds and the classification in the two-dimensional case, comparing our theory with classical results for nef tangent bundle or non-negative bisectional curvature. Related open problems will be discussed if time permits.
This is joint work with Genki Hosono (Tohoku University) and Masataka Iwai (Osaka City University).
[ Reference URL ]
https://zoom.us/meeting/register/tJ0vcu2rrDIqG9Rv5AT0Mpi37urIkJ1IRldB

2020/10/12

10:30-12:00   Online
NOGUCHI Junjiro (University of Tokyo)
Two topics on psedoconvex domains (Japanese)
[ Reference URL ]
https://zoom.us/meeting/register/tJ0vcu2rrDIqG9Rv5AT0Mpi37urIkJ1IRldB

2020/07/13

10:30-12:00   Online
INOUE Eiji (University of Tokyo)
$\mu$-cscK metrics and $\mu$K-stability of polarized manifolds
[ Reference URL ]
https://forms.gle/vSFPoVR6ugrkTGhX7

2020/07/06

10:30-12:00   Online
INAYAMA Takahiro (University of Tokyo)
Nakano positivity of singular Hermitian metrics and vanishing theorems of Demailly-Nadel-Nakano type (Japanese?)
[ Abstract ]
We propose a general definition of Nakano semi-positivity of singular Hermitian metrics on holomorphic vector bundles. By using this positivity notion, we establish $L^2$-estimates for holomorphic vector bundles with Nakano positive singular Hermitian metrics. We also show vanishing theorems, which generalize both Nakano type and Demailly-Nadel type vanishing theorems.
[ Reference URL ]
https://forms.gle/vSFPoVR6ugrkTGhX7

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