Searcharxiv⌕ Search

arXiv subjects

Yum-Tong Siu

Publications and source records attributed to Yum-Tong Siu.

At least 19 recordsLinked to original sources
arXiv2023

Effective Kohn Algorithm for Special Domain Defined by Functions Depending on All Variables

Kohn introduced in 1979 the algorithm of multipliers to study the subelliptc estimate of the $\bar\partial$-Neumann problem for a smooth weakly pseudoconvex domain in a complex Euclidean space which satisfies D'Angelo's finite type condition of a finite bound for the normalized touching order to the boundary for any local possibly singular holomorphic curve in the complex Euclidean space. The problem can be regarded as an example of the formulation of Hörmander's 1967 hypoelliptic result for the case of complex-valued vector-valued unknowns. So far the effective solution of Kohn's problem is known only for special domains ${\rm Re}(z_{n+1})+\sum_{j=1}^N|f_j|^2<0$ in ${\mathbb C}^{n+1}$ with $f_j$ holomorphic in $z_1,...,z_n$, because for such domains it suffices to deal with holomorphic multipliers. One main obstacle to treat the general smooth case is the need to deal with nonholomorphic multipliers. This note introduces a new technique to handle nonholomorphic multipliers occurring in more general domains with $f_j$ holomorphic in all the $n+1$ variables $z_1,...,z_n,z_{n+1}$.

math.CV↗
arXiv2022

The Role of the Gradient Term of the Bochner-Kodaira Formula in Coherent Sheaf Extension

In applying the Bochner-Kodaira formula with boundary term to solve the $\bar\partial$ equation with $L^2$ estimates, the gradient term is usually not used. Two potentially important applications of the use of the gradient term are the strong rigidity for holomorphic vector bundles and the very ampleness part of the Fujita conjecture. In this note we use the gradient term to construct holomorphic sections to prove the Thullen-type extension across codimension $1$ for holomorphic vector bundles with Hermitian metric whose curvature is $L^p$ for some $p>1$. This construction of sections points out a typical way of how the gradient term can be used.

math.CV↗
arXiv2018

Skoda's Ideal Generation from Vanishing Theorem for Semipositive Nakano Curvature and Cauchy-Schwarz Inequality for Tensors

Skoda's 1972 result on ideal generation is a crucial ingredient in the analytic approach to the finite generation of the canonical ring and the abundance conjecture. Special analytic techniques developed by Skoda, other than applications of the usual vanishing theorems and L2 estimates for the d-bar equation, are required for its proof. This note (which is part of a lecture given in the 60th birthday conference for Lawrence Ein) gives a simpler, more straightforward proof of Skoda's result, which makes it a natural consequence of the standard techniques in vanishing theorems and solving d-bar equation with L2 estimates. The proof involves the following three ingredients: (i) one particular Cauchy-Schwarz inequality for tensors with a special factor which accounts for the exponent of the denominator in the formulation of the integral condition for Skoda's ideal generation, (ii) the nonnegativity of Nakano curvature of the induced metric of a special co-rank-1 subbundle of a trivial vector bundle twisted by a special scalar weight function, and (iii) the vanishing theorem and solvability of d-bar equation with L2 estimates for vector bundles of nonnegative Nakano curvature on a strictly pseudoconvex domain. Our proof gives readily other similar results on ideal generation.

math.CV↗
arXiv2017

New Procedure to Generate Multipliers in Complex Neumann Problem and Effective Kohn Algorithm

The purpose of this note is threefold. (i) To explain the effective Kohn algorithm for multipliers in the complex Neumann problem and its difference with the full-real-radical Kohn algorithm, especially in the context of an example of Catlin-D'Angelo concerning the ineffectivness of the latter. (ii) To extend the techniques of multiplier ideal sheaves for the complex Neumann problem to general systems of partial differential equations. (iii) To present a new procedure of generation of multipliers in the complex Neumann problem as a special case of the multiplier ideal sheaves techniques for general systems of partial differential equation.

math.CV↗
arXiv2015

Splitting of unstable 2-bundles over the complex projective 6-space

We prove that any unstable holomorphic 2-bundle over the complex projective space of complex dimension n at least 6 must split into a direct sum of two holomorphic line bundles. The statement with the weaker dimension condition of n at least 4 has been an open conjecture since 1977. One ingredient in our method uses Mathias Peternell's singular variety version of the Barth-Lefschetz theorem which requires the strong dimension condition of n at least 6.

math.CV↗
arXiv2015

Hyperbolicity of Generic High-Degree Hypersurfaces in Complex Projective Space

We use two ingredients to prove the hyperbolicity of generic hypersurfaces of sufficiently high degree and of their complements in the complex projective space. One is the pullbacks of appropriate low pole order meromorphic jet differentials on the complex projective space to a hypersurface. The other is slanted vector fields of low vertical pole order on the vertical jet space of the universal hypersurface. We also present a number of related results, obtained by the same methods, such as: (i) a Big-Picard-Theorem type statement concerning extendibility, across the puncture, of holomorphic maps from a punctured disk to a generic hypersurface of high degree, (ii) nonexistence of nontrivial sets of entire functions satisfying certain polynomial equations with slowly varying coefficients, and (iii) Second Main Theorems for jet differentials and slowly moving targets.

math.CV↗
arXiv2011

Section Extension from Hyperbolic Geometry of Punctured Disk and Holomorphic Family of Flat Bundles

The construction of sections of bundles with prescribed jet values plays a fundamental role in problems of algebraic and complex geometry. When the jet values are prescribed on a positive dimensional subvariety, it is handled by theorems of Ohsawa-Takegoshi type which give extension of line bundle valued square-integrable top-degree holomorphic forms from the fiber at the origin of a family of complex manifolds over the open unit 1-disk when the curvature of the metric of line bundle is semipositive. We prove here an extension result when the curvature of the line bundle is only semipositive on each fiber with negativity on the total space assumed bounded from below and the connection of the metric locally bounded, if a square-integrable extension is known to be possible over a double point at the origin. It is a Hensel-lemma-type result analogous to Artin's application of the generalized implicit function theorem to the theory of obstruction in deformation theory. The motivation is the need in the abundance conjecture to construct pluricanonical sections from flatly twisted pluricanonical sections. We also give here a new approach to the original theorem of Ohsawa-Takegoshi by using the hyperbolic geometry of the punctured open unit 1-disk to reduce the original theorem of Ohsawa-Takegoshi to a simple application of the standard method of constructing holomorphic functions by solving the d-bar equation with cut-off functions and additional blowup weight functions.

math.CV↗
arXiv2010

Abundance conjecture

We sketch a proof of the abundance conjecture that the Kodaira dimension of a compact complex algebraic manifold equals its numerical Kodaira dimension. The proof consists of the following three parts: (i) the case of numerical Kodaira dimension zero, (ii) the general case under the assumption of the coincidence of the numerically trivial foliation and fibration for the canonical bundle, and (iii) the verification of the coincidence of the numerically trivial foliation and fibration for the canonical bundle. Besides the use of standard techniques such as the L2 estimates of d-bar, the first part uses Simpson's method of replacing the flat line bundle in a nontrivial flatly twisted canonical section by a torsion flat line bundle. Simpson's method relies on the technique of Gelfond-Schneider for the solution of the seventh problem of Hilbert. The second part uses the semi-positivity of the direct image of a relative pluricanonical bundle. The third part uses the technique of the First Main Theorem of Nevanlinna theory and its use is related to the technique of Gelfond-Schneider in the first part.

math.AG↗
arXiv2009

Dynamic multiplier ideal sheaves and the construction of rational curves in Fano manifolds

This note is written for the Festschrift in honor of Professor Christer Kiselman. Multiplier ideal sheaves identify the location and the extent of the failure of crucial estimates. In this note we will discuss and explain the historic evolution of the notion of multiplier ideal sheaves, especially the interpretation from the viewpoint of destabilizing subsheaves in the context of terminating or bounding an infinite process. We will also discuss the approach of constructing rational curves in Fano manifolds by using dynamic multiplier ideal sheaves and singularity-magnifying complex Monge-Ampere equations. This approach is still under development with details in the process of being worked out. We will indicate where details still need to be worked out.

math.CV↗
arXiv2008

Techniques for the Analytic Proof of the Finite Generation of the Canonical Ring

This article is written for the Proceedings of the Conference on Current Developments in Mathematics in Harvard University, November 16-17, 2007. It is an exposition of the analytic proof of the finite generation of the canonical ring for a compact complex algebraic manifold of general type. It lists and discusses the main techniques and explains how they are put together in the proof. Of the various main techniques some special attention is given to (i) the technique of discrepancy subspaces and (ii) the technique of subspaces of minimum additional vanishing.

math.AG↗
arXiv2008

Effective Termination of Kohn's Algorithm for Subelliptic Multipliers

This note discusses the problem of the effective termination of Kohn's algorithm for subelliptic multipliers for bounded smooth weakly pseudoconvex domains of finite type. We give a complete proof for the case of special domains of finite type and indicate briefly how this method is to be extended to the case of general bounded smooth weakly pseudoconvex domains of finite type.

math.CV↗
arXiv2008

Finite Generation of Canonical Ring by Analytic Method

In the 80th birthday conference for Professor LU Qikeng in June 2006 I gave a talk on the analytic approach to the finite generation of the canonical ring for a compact complex algebraic manifold of general type. This article is my contribution to the proceedings of that conference from my talk. In this article I give an overview of the analytic proof and focus on explaining how the analytic method handles the problem of infinite number of interminable blow-ups in the intuitive approach to prove the finite generation of the canonical ring. The proceedings of the LU Qikeng conference will appear as Issue No. 4 of Volume 51 of Science in China Series A: Mathematics (www.springer.com/math/applications/journal/11425).

math.CV↗
arXiv2006

A General Non-Vanishing Theorem and an Analytic Proof of the Finite Generation of the Canonical Ring

On August 5, 2005 in the American Mathematical Society Summer Institute on Algebraic Geometry in Seattle and later in several conferences I gave lectures on my analytic proof of the finite generation of the canonical ring for the case of general type. After my lectures many people asked me for a copy of the slides which I used for my lectures. Since my slides were quite sketchy because of the time limitation for the lectures, I promised to post later on a preprint server my detailed notes from which my slides were extracted. Here are my detailed notes giving the techniques and the proof.

math.AG↗
arXiv2005

Multiplier ideal sheaves in complex and algebraic geometry

This article discusses the geometric application of the method of multiplier ideal sheaves. It first briefly describes its application to effective problems in algebraic geometry and then presents and explains its application to the deformational invariance of plurigenera for general compact algebraic manifolds. Finally its application to the conjecture of the finite generation of the canonical ring is explored and the use of complex algebraic geometry in complex Neumann estimates is discussed.

math.AG↗
arXiv2002

Some recent transcendental techniques in algebraic and complex geometry

This article discusses the recent transcendental techniques used in the proofs of the following three conjectures. (1)~The plurigenera of a compact projective algebraic manifold are invariant under holomorphic deformation. (2)~There exists no smooth Leviflat hypersurface in the complex projective plane. (3)~A generic hypersurface of sufficiently high degree in the complex projective space is hyperbolic in the sense that there is no nonconstant holomorphic map from the complex Euclidean line to it.

math.CV↗
arXiv2002

Addendum to ``Defects for ample divisors of abelian varieties, Schwarz lemma, and hyperbolic hypersurfaces of low degrees,'' Amerian Journal of Mathematics 119 (1997), 1139-1172

This is an addendum to our earlier paper on the defect of an ample divisor of an abelian variety. It modifies an argument of the original paper to handle one difficulty there. At the same time the modification improves the result in the original paper by replacing the counting function by one truncated at a multiplicity given by an explicit function of the dimension of the abelian variety and the Chern number of the divisor.

math.CV↗
arXiv2000

Nonexistence of smooth Levi-flat hypersurfaces in complex projective spaces of dimension >= 3

In this paper we prove the following theorem. Main Theorem. Let n >= 3 and m >= 3n/2 +7. Then there exists no C^m Levi-flat real hypersurface M in P_n. The condition that M is Levi-flat means that when M is locally defined by the vanishing of a C^m real-valued function f, at every point of M the restriction of d d-bar f to the complex tangent space of M is identically zero. The case of the nonexistence of C^\infty Levi-flat real hypersurface in P_2 is motivated by problems in dynamical systems in P_2.

math.CV↗