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arXiv 1903.05967math.AG
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分次线性级数的渐近结构与不变量

Asymptotic constructions and invariants of graded linear series

Chih-Wei Chang, Shin-Yao Jow

摘要:

设$X$是代数闭域$\mathbf{K}$上维数$n$的完全簇。令$V_\bullet$是与$X$上的线丛$L$相关联的分次线性级数,即,向量子空间$V_m\subseteq H^0(X,L^{\otimes m})$的集合$\{V_m\}_{m\in\mathbb{N}}$,使得对于所有$k,\ell\in\mathbb{N}$,$V_0=\mathbf{K}$和$V_k\cdot V_\ell\subseteq V_{k+\ell}$。对于半群\[ \mathbf{N}(V_\bullet)=\{m\in\mathbb{N}\mid V_m\ne 0\},\]中的每个$m$,线性序列$V_m$定义了一个有理映射\[ ϕ_m\colon X\dashrightarrow Y_m\subseteq\mathbb{P}(V_m), \],其中$Y_m$表示像$ϕ_m(X)$的闭包。我们表明,对于所有足够大的$m\in \mathbf{N}(V_\bullet)$,这些合理的地图$ϕ_m\colon X\dashrightarrow Y_m$是双有理等价的,所以特别是$Y_m$是相同的尺寸$κ$,如果$κ=n$然后$ϕ_m\colon X\dashrightarrow Y_m$是一般有限的相同程度。如果$\mathbf{N}(V_\bullet)\ne\{0\}$,我们证明极限\[ \operatorname{vol}_κ(V_\bullet)=\lim_{m\in \mathbf{N}(V_\bullet)}\frac{\dim_\mathbf{K} V_m}{m^κ/κ!}\]存在,并且$0<\operatorname{vol}_κ(V_\bullet)<\infty$。此外,如果$Z\subseteq X$是维数$κ$的一般闭子簇,则极限\[ (V_\bullet^κ\cdot Z)_\text{mov}=\lim_{m\in \mathbf{N}(V_\bullet)}\frac{\#\bigl((D_{m,1}\cap\cdots\cap D_{m,κ}\cap Z)\setminus \operatorname{Bs}(V_m)\bigr)}{m^κ}\]存在,其中$D_{m,1},\ldots,D_{m,κ}\in |V_m|$是一般因子,并且\[ (V_\bullet^κ\cdot Z)_\text{mov}=\operatorname{deg}\bigl(ϕ_m|_Z\colon Z\dashrightarrow ϕ_m(Z)\bigr)\operatorname{vol}_κ(V_\bullet) \]对于所有足够大的$m\in\mathbf{N}(V_\bullet)$。

英文摘要:

Let $X$ be a complete variety of dimension $n$ over an algebraically closed field $\mathbf{K}$. Let $V_\bullet$ be a graded linear series associated to a line bundle $L$ on $X$, that is, a collection $\{V_m\}_{m\in\mathbb{N}}$ of vector subspaces $V_m\subseteq H^0(X,L^{\otimes m})$ such that $V_0=\mathbf{K}$ and $V_k\cdot V_\ell\subseteq V_{k+\ell}$ for all $k,\ell\in\mathbb{N}$. For each $m$ in the semigroup \[ \mathbf{N}(V_\bullet)=\{m\in\mathbb{N}\mid V_m\ne 0\},\] the linear series $V_m$ defines a rational map \[ ϕ_m\colon X\dashrightarrow Y_m\subseteq\mathbb{P}(V_m), \] where $Y_m$ denotes the closure of the image $ϕ_m(X)$. We show that for all sufficiently large $m\in \mathbf{N}(V_\bullet)$, these rational maps $ϕ_m\colon X\dashrightarrow Y_m$ are birationally equivalent, so in particular $Y_m$ are of the same dimension $κ$, and if $κ=n$ then $ϕ_m\colon X\dashrightarrow Y_m$ are generically finite of the same degree. If $\mathbf{N}(V_\bullet)\ne\{0\}$, we show that the limit \[ \operatorname{vol}_κ(V_\bullet)=\lim_{m\in \mathbf{N}(V_\bullet)}\frac{\dim_\mathbf{K} V_m}{m^κ/κ!}\] exists, and $0<\operatorname{vol}_κ(V_\bullet)<\infty$. Moreover, if $Z\subseteq X$ is a general closed subvariety of dimension $κ$, then the limit \[ (V_\bullet^κ\cdot Z)_\text{mov}=\lim_{m\in \mathbf{N}(V_\bullet)}\frac{\#\bigl((D_{m,1}\cap\cdots\cap D_{m,κ}\cap Z)\setminus \operatorname{Bs}(V_m)\bigr)}{m^κ}\] exists, where $D_{m,1},\ldots,D_{m,κ}\in |V_m|$ are general divisors, and \[ (V_\bullet^κ\cdot Z)_\text{mov}=\operatorname{deg}\bigl(ϕ_m|_Z\colon Z\dashrightarrow ϕ_m(Z)\bigr)\operatorname{vol}_κ(V_\bullet) \] for all sufficiently large $m\in\mathbf{N}(V_\bullet)$.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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