P^1的Gauss复合与双覆盖Hurwitz空间的泛Jacobian
Gauss Composition for P^1, and the universal Jacobian of the Hurwitz space of double covers
摘要：
利用亏格为g的曲线研究了P^1的双覆盖Hurwitz堆上n次线丛的泛雅可比矩阵.我们的主要结果是：一个光滑的，不可约的，普遍封闭的（但不分离）模紧化的普遍雅可比矩阵的建设;一个描述的全球几何形状和这些堆栈的模属性;和计算的皮卡德集团这些堆栈的情况下，当n-g是偶数。我们工作的一个重要组成部分是二元二次型参数化双覆盖上的线丛。这种参数化推广了二次环的理想类与整数二元二次型之间的经典数论对应，特别是给出了Gauss首次发现的整数二元二次型的群律.
英文摘要：
We investigate the universal Jacobian of degree n line bundles over the Hurwitz stack of double covers of P^1 by a curve of genus g. Our main results are: the construction of a smooth, irreducible, universally closed (but not separated) moduli compactification of this universal Jacobian; a description of the global geometry and moduli properties of these stacks; and a computation of the Picard groups of these stacks in the cases when n-g is even. An important ingredient of our work is the parametrization of line bundles on double covers by binary quadratic forms. This parametrization generalizes the classical number theoretic correspondence between ideal classes of quadratic rings and integral binary quadratic forms, which in particular gives the group law on integral binary quadratic forms first discovered by Gauss.
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