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arXiv 2603.01445math.AGmath.NT
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曲线的覆盖,Ceresa环与意外交集

Covers of curves, Ceresa cycles, and Unlikely intersections

The Ohio State University(俄亥俄州立大学);University of Maine(缅因大学);University of California, San Diego(加利福尼亚大学圣地亚哥分校);Boston University(波士顿大学)

Tejasi Bhatnagar, Sheela Devadas, Toren D'Nelly-Warady, Padmavathi Srinivasan

AI总结:

研究通过将Ceresa环与雅可比群中的点关联,证明了非常一般的分叉覆盖曲线的Ceresa环在雅可比群中非 torsion,并给出了具体例子。

摘要:

给定一个光滑的、项目性的、几何上积分的曲线C,其亏格g≥2,其上特征为零的域。我们证明,对于非常一般的分叉覆盖C̃,其Ceresa环Cer( C̃ )在其雅可比群中是非 torsion 的。我们还显示,存在无限多个分叉覆盖的家族,其中这些家族对应于具有非 torsion Ceresa环的曲线。为了说明这一点,我们给出了两个具体的1维和2维亏格为6的曲线族,其中具有 torsion Ceresa环的定位是扎里斯基闭的且具有正的余维数。我们的策略是将Ceresa环是否为 torsion 的问题转化为与曲线雅可比群中相关点是否为 torsion 的问题。为此,我们使用Ceresa环的“相对canonical shadow”,这是通过将Ceresa环与由覆盖映射自然产生的对应关系相交得到的雅可比群中的点。我们结合了意外交集理论(即相对Manin-Mumford定理)的思想,来研究Ceresa环的相对canonical shadow成为torsion的定位。

英文摘要:

Fix a smooth, projective, geometrically integral curve $C$ of genus $g \geq 2$ over a characteristic zero field. We prove that the Ceresa cycle $\mathrm{Cer}(\widetilde{C})$ of a very general ramified cover $\widetilde{C}$ of $C$ is nontorsion in the Chow group of its Jacobian. We also show that there exist infinitely many families of ramified covers of a varying family of curves where a general point of these families corresponds to a curve with nontorsion Ceresa cycle. To illustrate this, we write down two explicit $1$-dimensional and $2$-dimensional families of genus $6$ curves where the locus of curves with torsion Ceresa cycle is Zariski closed and has positive codimension. Our strategy is to reduce the question of whether the Ceresa cycle is torsion to the question of whether a related point on the Jacobian of the curve is torsion. For this, we use the ``relative canonical shadow" of the Ceresa cycle, which is a point in the Jacobian of the curve obtained by intersecting the Ceresa cycle with a natural correspondence arising from the covering map. We combine this with ideas from unlikely intersection theory (namely the relative Manin--Mumford theorem) to study the locus where the relative canonical shadows of the Ceresa cycle become torsion.

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