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arXiv math/0309456math.AG
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曲线上的Frobenius-不稳定秩2向量丛

On Frobenius-destabilized rank-2 vector bundles over curves

Herbert Lange, Christian Pauly

摘要:

设X是特征p > 0的代数闭域k上亏格g \geq 2的光滑射影曲线.设M_X是X上半稳定秩2的具有平凡行列式的向量丛的模空间。相对Frobenius映射F:X \to X_1通过拉回诱导有理映射V:M_{X_1} \to M_{X}。在本文中,我们展示了以下结果。1)对X上的任意线丛L,秩为p的向量丛F_*L是稳定的. 2)有理映射V具有基点,即,存在X_1上的稳定丛E使得F^* E不是半稳定的。3)设B \subset M_{X_1}表示V的概型理论基轨迹.若g=2,p>2且X为常值,则B是长为{2/3}p(p^2 - 1)的0维局部完全交,V的次数等于{1/3}p(p^2 + 2).

英文摘要:

Let X be a smooth projective curve of genus g \geq 2 over an algebraically closed field k of characteristic p > 0. Let M_X be the moduli space of semistable rank-2 vector bundles over X with trivial determinant. The relative Frobenius map F: X \to X_1 induces by pull-back a rational map V: M_{X_1} \to M_{X}. In this paper we show the following results. 1) For any line bundle L over X, the rank-p vector bundle F_*L is stable. 2) The rational map V has base points, i.e., there exist stable bundles E over X_1 such that F^* E is not semistable. 3) Let B \subset M_{X_1} denote the scheme-theoretical base locus of V. If g=2, p>2 and X ordinary, then B is a 0-dimensional local complete intersection of length {2/3}p(p^2 -1) and the degree of V equals {1/3}p(p^2 +2).

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