穿孔曲面上主可加丛的仿射扩张
Affine extensions of principal additive bundles over a punctured surface
摘要：
本文的目的是使复杂的正常仿射$\mathbb G_a$ -三倍$X$的分类的第一步。我们考虑商态射$π\colon X\to S$到$π^{-1}(S_*)$的限制是主$\mathbb G_a$ -丛的情况，其中$S_*$表示$S$中某个正则闭点的补。品种$\mathrm{SL}_2$将是特别感兴趣的和许多例子的来源。它有一个自然的右$\mathbb G_a$ -作用，使得商态射$\mathrm{SL}_2\to\mathbb A^2$限制于穿孔平面$\mathbb A^2_*$上的主$\mathbb G_a$ -丛。
英文摘要：
The aim of this article is to make a first step towards the classification of complex normal affine $\mathbb G_a$-threefolds $X$. We consider the case where the restriction of the quotient morphism $π\colon X\to S$ to $π^{-1}(S_*)$, where $S_*$ denotes the complement of some regular closed point in $S$, is a principal $\mathbb G_a$-bundle. The variety $\mathrm{SL}_2$ will be of special interest and a source of many examples. It has a natural right $\mathbb G_a$-action such that the quotient morphism $\mathrm{SL}_2\to\mathbb A^2$ restricts to a principal $\mathbb G_a$-bundle over the punctured plane $\mathbb A^2_*$.
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