Takeshi Kawachi
We give the new effective criterion for the global generation of the adjoint bundle on normal surfaces with a boundary. We could make the invariant δsmall a bit more on log-terminal singular point, and then we could prove the theorem described in my previous paper "alg-geom/9612018" as a corollary.
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For a polarized abelian variety $(X,L)$, Z. Jiang and G. Pareschi introduce an invariant $β(X,L)$, called the basepoint-freeness threshold. Using this invariant, we show that a general polarized abelian variety $(X,L)$ of dimension $g$ is projectively normal if $χ(L) \geq 2^{2g-1}$ and the type of $L$ is not $(2,4,\dots,4)$. This bound is sharp since it is known that any polarized abelian variety of type $(2,4,\dots,4)$ is not projectively normal. We also give an application of $β(X,L)$ to the Infinitesimal Torelli Theorem for $Y \in |L|$.
This treats the base-point-freeness of the adjoint bundles on normal surfaces with a boundary. This is an extension of the non-relative version of the theorem of Ein-Lazarsfeld-Masek and the theorem of Kawachi-Masek.
Let $X$ be a complete normal variety, $B$ an effective $\mathbb{R}$-divisor on $X$, and $D$ a Cartier divisor on $X$. Assume that the pair $(X, B)$ is log terminal. We consider the problem whether $H^0(X, D) \ne 0$ and obtain some results in lower dimensions.
We extend Reider's freeness criterion to normal surfaces of characteristic 0. Let Y be a normal surface. Let D be a nef divisor on Y such that K_Y+D is a Cartier divisor. Let x be a point on Y. If x is a base point of |K_Y+D| and D^2>δ_x (δ_x is determined by x, δ_x <= 4) then there exists a non zero effective divisor E on Y passing through x such that 0 <= DE <= δ_x /2, DE - δ_x /4 <= E^2 <= (DE)^2 / D^2, E^2 < 0 if DE=0.
On torsion-freeness of Kähler differential sheaves
该研究在特征零代数闭域上的正规代数簇中，给出了Kähler微分层无挠性的等价刻画：其一阶形变理想层的正则截面可从奇点轨迹外延拓至奇点轨迹。
Remarks on basepoint-freeness thresholds of polarized abelian surfaces
本文确定了非常一般的极化阿贝尔表面在复数域上的基点自由阈值，并给出了第一个基点自由阈值为无理数的极化阿贝尔表面的例子。
In this note, we study base point freeness up to taking p-power, which we will call p-power freeness. We first establish some criteria for p-power freeness as analogues of criteria for semi-ampleness. We then apply these results to three-dimensional birational geometry.
For abelian surfaces of Picard rank 1, we perform explicit computations of the cohomological rank functions of the ideal sheaf of one point, and in particular of the basepoint-freeness threshold. Our main tool is the relation between cohomological rank functions and Bridgeland stability. In virtue of recent results of Caucci and Ito, these computations provide new information on the syzygies of polarized abelian surfaces.
An Inductive Approach to Basepoint-Freeness of Adjoint Series on Irregular Varietiess
本文提出一种归纳方法证明不规则簇上线性系统的无基点性，并在温和条件下证明Fujita猜想对具nef反典范丛的n维不规则簇成立。
Towards generic base-point-freeness for hyperkähler manifolds of generalized Kummer type
本文研究广义 Kummer 型超凯勒流形上大且 nef 线丛的无基点性，证明了在低维及可除性为 1 时，模空间中一般极化无基点。
We prove Fujita-type basepoint-freeness for projective quasi-log canonical curves and surfaces.
Let $X$ be a smooth projective variety of dimension $5$ and $L$ be an ample line bundle on $X$. We show that $|K_X + 6L|$ is base-point free.
We obtain effective results for the global generation of pluritheta line bundles on moduli spaces of vector bundles on curves. The main ingredient is an independent result giving an upper bound on the dimension of the Hilbert scheme of coherent quotients of a given vector bundle.
In this note we establish a new Fujita-type effective bound for the base point freeness of adjoint line bundles on a compact complex projective manifold of complex dimension $n$. The bound we obtain (approximately) differs from the linear bound conjectured by Fujita only by a factor of the cube root of $n$. As an application, a new effective statement for pluricanonical embeddings is derived.
On base point freeness for rank one foliations
本文研究了秩为一的叶形在Q-因子有限准正则三重域上的基点自由性，并在数值上平凡的情况下证明了其丰盈性。
Deformations, local freeness, and base change for higher Du Bois singularities
该研究证明严格高阶Du Bois奇点在小形变下不变，针对严格高阶Du Bois纤维的相对Du Bois复形建立基变换定理，展示1-Du Bois纤维的相关失效并推广局部自由性定理、证明Hodge数不变性。
A necessary and sufficient condition is given for semi-ampleness of a numerically effective (nef) and big line bundle in positive characteristic. One application is to the geometry of the universal stable curve over M_g, specifically, the semi-ampleness of the relative dualizing sheaf, in positive characteristic. An example is given which shows this and the semi-ampleness criterion fail in characteristic zero. A second application is to Mori's program for minimal models of 3-folds in positive characteristic, namely, to the existence of birational extremal contractions.
We prove that if $(X,A+B)$ is a pair defined over an algebraically closed field of positive characteristic such that $(X,B)$ is strongly $F$-regular, $A$ is ample and $K_X+A+B$ is strictly nef, then $K_X+A+B$ is ample. Similarly, we prove that for a log pair $(X,A+B)$ with $A$ being ample and $B$ effective, $K_X+A+B$ is big if it is nef and of maximal nef dimension. As an application, we establish a rationality theorem for the nef threshold and various results towards the minimal model program in dimension three in positive characteristic.
This paper proposes a Fujita-type freeness conjecture for semi-log canonical pairs. We prove it for curves and surfaces by using the theory of quasi-log schemes and give some effective very ampleness results for stable surfaces and semi-log canonical Fano surfaces. We also prove an effective freeness for log surfaces.
I give a necessary and sufficient condition for a nef and big line bundle in positive characteristic to be semi-ample, and then give two applications: I show that the relative dualizing sheaf of the universal curve is semi-ample, in positive characteristic, and give a simple example which shows that this, and the semi-ampleness criterion, fail in characteristic zero. My second application is to Mori's program for minimal models of 3-folds. I prove a version of the Basepoint Free Theorem (for big line bundles on 3-folds of positive characteristic) and a simple Cone Theorem, for 3-folds of posit…
We prove Angehrn-Siu type effective base point freeness and point separation for log canonical pairs.
A solution to Fujita's freeness conjecture via an extension theorem with analytic adjoint ideal sheaves
本文利用伴随理想层对乘子理想层不可积轨迹的精细控制，并结合基于内射性定理技术的扩张定理，直接处理 lc 奇点及其极小 lc 中心，从而在 Angehrn-Siu 思路下解决了藤田有效自由性猜想。
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