arXiv subjects
Publications and source records attributed to 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.
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.
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.
Let $(X,L)$ be an $n$-dimensional polarized variety. Fujita's conjecture says that if $L^n>1$ then the adjoint bundle $K_X+nL$ is spanned and $K_X+(n+1)L$ is very ample. There are some examples such that $K_X+nL$ is not spanned or $K_X+(n+1)L$ is not very ample. These are $(¶^n,Ø(1))$, hypersurface $M$ of degree $6$ in weighted projective space $¶(3,2,1,1,\cdots ,1)$ with $Ø_M(1)$ and numerically Godeaux surface etc. Numerically Godeaux surface is the quotient space of a Fermat type hypersurface of degree $5$ in $¶^3$ by an action of order $5$. These examples are not so much. We construct new examples for any dimention.