arXiv subjects

Takao Fujita

Publications and source records attributed to Takao Fujita.

5 recordsLinked to original sources

arXiv1996

On Kodaira energy and adjoint reduction of polarized threefolds

Here we study and classify polarized threefolds whose Kodaira energies are less than -1/2. The Kodaira energy of a polarized manifold (M, L), a pair consisting of a smooth complex algebraic variety M and an ample line bundle L on it, is defined to be $-\Inf{t\in Q\vert κ(K+tL)\ge0}$, where K is the canonical bundle of M and $κ$ denotes the Iitaka dimension of a Q-bundle. The method is a variant of those in my paper; manuscripta math. 76(1992).

alg-geom↗

arXiv1995

A note on scrolls of smallest embedded codimension

Let $M$ be a submanifold of ${\Bbb P}^N$ of dimension $n>2$. Suppose that $(M,{\Cal O}_M(1))\cong{\Bbb P}({\Cal E}),{\Cal O}(1))$ for some vector bundle ${\Cal E}$ on a surface $S$. Then $N\ge 2n-1$ by Barth-Lefschetz Theorem. We are interested in the case $N=2n-1$. In 1994 Ionescu and Toma gave a classification of the cases where $S$ is not of general type. Here we propose a conjecture concerning this remaining case, which is verified for $n\le 1100$ by a computer programm.

alg-geom↗

arXiv1994

Towards a separation theorem of points by adjoint linear systems on polarized threefolds

Main Result: Let $(M,L)$ be a smooth complex polarized threefold. Then the linear system $| K+tL|$ separates any two different points on $M$ for any $t\ge 6$, where $K$ is the canonical bundle of $M$. The argument in the proof is a variant of Ein-Lazarsfeld method. Although it is less powerful, it is cheaper, i.e., needs fewer pages. Unfortunately, at present, I cannot show the very ampleness because of technical difficulties. Some related topics are also discussed. A hard copy is available on request to the author.

alg-geom↗

arXiv1993

Remarks on Ein-Lazarsfeld criterion of spannedness of adjoint bundles of polarized threefolds

Let B be a nef and big line bundle on a smooth complex threefold X with canonical bundle K. Let x be a point on X and suppose that BC\ge3 for any curve C passing x, B^2S\ge7 for any surface S containing x, and B^3\ge51. Then K+B is spanned at x. (Ein-Lazarsfeld proved the assertion assuming B^3\ge92.) Corollary: K+3L is spanned if L is an ample line bundle with L^3>1.

alg-geom↗

arXiv1992

Notes on Kodaira energies of polarized varieties

The Kodaira energy of a polarized manifold (M,L) is defined by κε(M,L)=-Inf{t\in Q|κ(K+tL)\ge 0}. Here we propose a couple of conjectures and announce several partial results. 3-dimensional cases are mainly considered. A hard copy is available on request to the author.

alg-geom↗