arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 1102.1093math.AG
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平面有理曲线与切丛的分裂

On plane rational curves and the splitting of the tangent bundle

Alessandro Gimigliano, Brian Harbourne, Monica Idà

摘要:

给定浸入$ϕ: P^1 \to ¶^2$,我们给出了确定余切丛拉回分裂的新方法。我们还给出了新的边界上的分裂类型的浸入因子为$ϕ: P^1 \cong D \subset X \to P^2$,其中$X \to P^2$是通过炸毁$r$不同的点$p_i \in P^2$。作为点$p_i$是一般的情况下的应用,我们给出了当$r \leq 7$。特别关注$D^2=-1$的病例。对于$r \leq8$类属点,已知只有1000个$ϕ$与$D^2=-1$不等价,并且它们都具有平衡分裂。然而,对于$r=9$类属点,我们发现有无穷多个不等价的$ϕ$与$D^2=-1$具有不平衡分裂(只有两个这样的例子是已知的)。我们发现,这些新的例子是相关的半伴随公式,我们猜想占所有发生的不平衡分裂时,$D^2=-1$的情况下,$r=9$通用点$p_i$。在最后一节中,我们将这些结果应用于研究胖点格式的分解。

英文摘要:

Given an immersion $ϕ: P^1 \to ¶^2$, we give new approaches to determining the splitting of the pullback of the cotangent bundle. We also give new bounds on the splitting type for immersions which factor as $ϕ: P^1 \cong D \subset X \to P^2$, where $X \to P^2$ is obtained by blowing up $r$ distinct points $p_i \in P^2$. As applications in the case that the points $p_i$ are generic, we give a complete determination of the splitting types for such immersions when $r \leq 7$. The case that $D^2=-1$ is of particular interest. For $r \leq8$ generic points, it is known that there are only finitely many inequivalent $ϕ$ with $D^2=-1$, and all of them have balanced splitting. However, for $r=9$ generic points we show that there are infinitely many inequivalent $ϕ$ with $D^2=-1$ having unbalanced splitting (only two such examples were known previously). We show that these new examples are related to a semi-adjoint formula which we conjecture accounts for all occurrences of unbalanced splitting when $D^2=-1$ in the case of $r=9$ generic points $p_i$. In the last section we apply such results to the study of the resolution of fat point schemes.

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