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arXiv 1109.6908math.AG
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用于极化曲线的GIT

GIT for polarized curves

Gilberto Bini, Fabio Felici, Margarida Melo, Filippo Viviani

摘要:

我们研究了极化曲线的GIT特性。更具体地说,我们研究了d-g维射影空间中亏格为g的d次曲线的Hilbert和Chow格式的GIT问题,当v:=d/(2g-2)减小时.我们证明,前三个值的v,在GIT常数的变化是由v=4,3.5,2。我们证明,当v>4时,L. Caporaso的结果对Hilbert和Chow半稳定性都成立。当3.5<v<4时,Hilbert半稳定轨迹与Chow半稳定轨迹重合,并映射到弱伪稳定曲线的模栈上。当2<v<3.5时,Hilbert和Chow半稳定轨迹重合,映射到伪稳定曲线的模叠加上。我们还详细分析了v=3.5和v=4的临界值,其中Hilbert半稳定轨迹严格小于Chow半稳定轨迹.作为应用,我们分别得到了稳定曲线、弱伪稳定曲线和伪稳定曲线的模空间上的泛Jacobian的三个紧化。

英文摘要:

We investigate GIT quotients of polarized curves. More specifically, we study the GIT problem for the Hilbert and Chow schemes of curves of degree d and genus g in a projective space of dimension d-g, as the ratio v:=d/(2g-2) decreases. We prove that the first three values of v at which the GIT quotients change are given by v=4, 3.5, 2. We show that, for v>4, L. Caporaso's results hold true for both Hilbert and Chow semistability. If 3.5<v<4, the Hilbert semistable locus coincides with the Chow semistable locus and it maps to the moduli stack of weakly-pseudo-stable curves. If 2<v<3.5, the Hilbert and Chow semistable loci coincide and they map to the moduli stack of pseudo-stable curves. We also analyze in detail the critical values v=3.5 and v=4, where the Hilbert semistable locus is strictly smaller than the Chow semistable locus. As an application, we obtain three compactifications of the universal Jacobian over the moduli space of stable curves, weakly-pseudo-stable curves and pseudo-stable curves, respectively.

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