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arXiv 1209.5409math.AGmath.CO
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稳定有理曲线密切旗的Schubert问题

Schubert problems with respect to osculating flags of stable rational curves

David E Speyer

摘要:

给定P^1中的一个点z,设F(z)是在点z处有理正态曲线的密切标志。本文研究了关于F(z_1),F(z_2),…,F(z_r)的研究,无论是经典的还是最近的,特别是当z_i为实数时.由于有理正态曲线具有PGL_2的作用,因此自然考虑点(z_1,.,z_r)为P ^1中r个相异点的模空间--著名的M_{0,r}。然后可以要求将Schubert交的结果推广到紧化\bar{M}_{0,r}。本文的第一部分实现了这一目标。我们在\bar{M}_{0,r}上构造了一个平坦的Cohen-Macaulay族,它的纤维在M_{0,r}上同构于G(d,n),并且给定划分为n,...,λ_r,我们构造了\bar{M}_{0,r}上的平坦Cohen-Macualay族,其纤维在(z_1,.,M_{0,r}中的f(z_r)是由lambda_i索引的舒伯特簇关于密切标志F(z_i)的交集。在本文的第二部分中,我们研究了sum |lambda_i| = dim G(d,n)的实点族的拓扑.我们证明了我们的族是\bar{M}_{0,r}的有限覆盖空间,并从Young tableaux理论给出了这个覆盖的一个明确的CW分解,其面由对象索引.

英文摘要:

Given a point z in P^1, let F(z) be the osculating flag to the rational normal curve at point z. The study of Schubert problems with respect to such flags F(z_1), F(z_2), ..., F(z_r) has been studied both classically and recently, especially when the points z_i are real. Since the rational normal curve has an action of PGL_2, it is natural to consider the points (z_1, ..., z_r) as living in the moduli space of r distinct point in P^1 -- the famous M_{0,r}. One can then ask to extend the results on Schubert intersections to the compactification \bar{M}_{0,r}. The first part of this paper achieves this goal. We construct a flat, Cohen-Macaulay family over \bar{M}_{0,r}, whose fibers over M_{0,r} are isomorphic to G(d,n) and, given partitions lambda_1, ..., lambda_r, we construct a flat Cohen-Macualay family over \bar{M}_{0,r} whose fiber over (z_1, ..., z_r) in M_{0,r} is the intersection of the Schubert varieties indexed by lambda_i with respect to the osculating flags F(z_i). In the second part of the paper, we investigate the topology of the real points of our family, in the case that sum |lambda_i| = dim G(d,n). We show that our family is a finite covering space of \bar{M}_{0,r}, and give an explicit CW decomposition of this cover whose faces are indexed by objects from the theory of Young tableaux.

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