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math.AG/0701466

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Title: Quotients of Calabi-Yau varieties
Authors: János Kollár, Michael Larsen
Categories: math.AG Algebraic Geometry (math.GR Group Theory)
Comments: Theorem 3 has been corrected. 27 pages
MSC: 14J32, 14K05, 20E99 (Primary) 14M20, 14E05, 20F55 (Secondary)

Abstract: Let $X$ be a complex Calabi-Yau variety, that is, a complex projective variety with canonical singularities whose canonical class is numerically trivial. Let $G$ be a finite group acting on $X$ and consider the quotient variety $X/G$. The aim of this paper is to determine the place of $X/G$ in the birational classification of varieties. That is, we determine the Kodaira dimension of $X/G$ and decide when it is uniruled or rationally connected.

If $G$ acts without fixed points, then $\kappa(X/G)=\kappa(X)=0$; thus the interesting case is when $G$ has fixed points. We answer the above questions in terms of the action of the stabilizer subgroups near the fixed points.

We give a rough classification of possible stabilizer groups which cause $X/G$ to have Kodaira dimension $-\infty$ or equivalently (as we show) to be uniruled. These stabilizers are closely related to unitary reflection groups.

Owner: Michael Larsen
Version 1: Wed, 17 Jan 2007 01:26:04 GMT
Version 2: Sun, 21 Jan 2007 19:08:21 GMT

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