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arXiv math/9903162math.AG
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代数群的本质维数与G-簇的一个分解定理

Essential dimensions of algebraic groups and a resolution theorem for G-varieties

Zinovy Reichstein, Boris Youssin, János Kollár, Endre Szabó

摘要:

设G是一个代数群,X是一个一般自由G-簇.我们证明了X可以通过一系列具有光滑G-等变中心的爆破变换为G-簇X',X'的每一点的稳定子同构于幂幺群U与可对角化群A的半直积.作为这一结果及相关结果的应用,我们证明了某些代数群的本质维数的新下界。我们还表明,某些多项式在一个变量不能简化的Tschirnhaus变换。

英文摘要:

Let G be an algebraic group and let X be a generically free G-variety. We show that X can be transformed, by a sequence of blowups with smooth G-equivariant centers, into a G-variety X' with the following property: the stabilizer of every point of X' is isomorphic to a semidirect product of a unipotent group U and a diagonalizable group A. As an application of this and related results, we prove new lower bounds on essential dimensions of some algebraic groups. We also show that certain polynomials in one variable cannot be simplified by a Tschirnhaus transformation.

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