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arXiv 0810.1148math.AGmath.AC
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Cox环、半群与仿射algebraic varieties的自同构

Cox rings, semigroups and automorphisms of affine algebraic varieties

Ivan V. Arzhantsev, Sergey A. Gaifullin

摘要:

我们研究仿射簇的Cox实现,即,正规仿射簇的一个典型表示,它具有一个由Neron-Severi拟托作用生成的除子类群作为一个因子分次仿射簇的商。对于有限群的线性作用的商空间,明确地描述了这种实现。证明了这一实现的一个泛性质,并给出了在这一背景下出现的抽象半群的因子理论的一些结果。我们表明,每一个仿射品种的自同构可以提升到一个自同构的Cox环规范化的分级。由此得出维数为$\geq 2$的非退化仿射复曲面簇的自同构群具有无穷维数。我们得到了一个野生的自同构的三维二次锥上升到Anick的自同构的多项式代数在四个变量。

英文摘要:

We study the Cox realization of an affine variety, i.e., a canonical representation of a normal affine variety with finitely generated divisor class group as a quotient of a factorially graded affine variety by an action of the Neron-Severi quasitorus. The realization is described explicitly for the quotient space of a linear action of a finite group. A universal property of this realization is proved, and some results on the divisor theory of an abstract semigroup emerging in this context are given. We show that each automorphism of an affine variety can be lifted to an automorphism of the Cox ring normalizing the grading. It follows that the automorphism group of a non-degenerate affine toric variety of dimension $\geq 2$ has infinite dimension. We obtain a wild automorphism of the three-dimensional quadratic cone that rises to Anick's automorphism of the polynomial algebra in four variables.

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