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arXiv 1302.5579math.AG
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关于射影空间的特殊二次双有理变换

On special quadratic birational transformations of a projective space

Giovanni Staglianò

摘要:

一个从射影空间到一个不太奇异的射影簇的双有理映射具有一个不可约的非奇异基轨迹方案(特殊的双有理变换)是一种罕见的现象,足以使分类结果有意义和简洁。我们将集中讨论由二次方程定义的变换到某些簇(特别是小度数的射影超曲面)上,令人惊讶的是,基轨迹是出现在其他上下文中的有趣的射影流形;例如,附加理论的例外,小度数或小余维流形,Severi或更一般的齐次簇。特别是,我们将分类:到二次超曲面的二次二次变换;到del Pezzo簇的四次三次变换;基轨迹(方案)的维度最多为三的变换。

英文摘要:

A birational map from a projective space onto a not too much singular projective variety with a single irreducible non-singular base locus scheme (special birational transformation) is a rare enough phenomenon to allow meaningful and concise classification results. We shall concentrate on transformations defined by quadratic equations onto some varieties (especially projective hypersurfaces of small degree), where quite surprisingly the base loci are interesting projective manifolds appearing in other contexts; for example, exceptions for adjunction theory, small degree or small codimensional manifolds, Severi or more generally homogeneous varieties. In particular, we shall classify: quadro-quadric transformations into a quadric hypersurface; quadro-cubic transformations into a del Pezzo variety; transformations whose base locus (scheme) has dimension at most three.

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