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arXiv 1303.4454math.AGmath.AT
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奇异环面簇的特征类

Characteristic classes of singular toric varieties

Laurentiu Maxim, Joerg Schuermann

摘要:

在本文中,我们计算的motivic陈类和同源Hirzebruch特征类(可能是奇异的)环面品种,这在完整的情况下,很好地符合广义Hirzebruch-Riemann-Roch定理。作为特殊情况,我们获得了新的(或恢复众所周知的)公式的Baum-Fulton-MacPherson托德(或MacPherson-Chern)类的复曲面品种,以及单投射复曲面品种的L-Milnor L-类。我们提出了两个不同的角度来计算这些特征类的复曲面品种。首先,我们利用环面-轨道分解和动机性质的动机陈和resp。的同源Hirzebruch类来表达后者的对偶层和resp。轨道闭包的(对偶)Todd类。这种方法甚至适用于给定复曲面簇的环面-不变子空间。然后将所得公式应用于格多面体及其子复形中的加权格点计数,得到广义Pick型公式。其次,在单纯复曲面品种的情况下,我们计算我们的特征类使用的Lefschetz-Riemann-Roch定理的Edidin-Graham的上下文中的几何商描述的品种。在这种情况下,我们定义模拟Hirzebruch类的单纯复曲面品种和调查(实际)同源Hirzebruch类和模拟Hirzebruch类之间的差异。我们表明,这种差异是本地化的奇异轨迹,我们得到一个公式,其中每个奇异锥的贡献明确确定。最后,将这两种计算特征类的方法结合起来,证明了Cappell和Shaneson在90年代初提出的几个示性类公式。

英文摘要:

In this paper we compute the motivic Chern classes and homology Hirzebruch characteristic classes of (possibly singular) toric varieties, which in the complete case fit nicely with a generalized Hirzebruch-Riemann-Roch theorem. As special cases, we obtain new (or recover well-known) formulae for the Baum-Fulton-MacPherson Todd (or MacPherson-Chern) classes of toric varieties, as well as for the Thom-Milnor L-classes of simplicial projective toric varieties. We present two different perspectives for the computation of these characteristic classes of toric varieties. First, we take advantage of the torus-orbit decomposition and the motivic properties of the motivic Chern and resp. homology Hirzebruch classes to express the latter in terms of dualizing sheaves and resp. the (dual) Todd classes of closures of orbits. This method even applies to torus-invariant subspaces of a given toric variety. The obtained formula is then applied to weighted lattice point counting in lattice polytopes and their subcomplexes, yielding generalized Pick-type formulae. Secondly, in the case of simplicial toric varieties, we compute our characteristic classes by using the Lefschetz-Riemann-Roch theorem of Edidin-Graham in the context of the geometric quotient description of such varieties. In this setting, we define mock Hirzebruch classes of simplicial toric varieties and investigate the difference between the (actual) homology Hirzebruch class and the mock Hirzebruch class. We show that this difference is localized on the singular locus, and we obtain a formula for it in which the contribution of each singular cone is identified explicitly. Finally, the two methods of computing characteristic classes are combined for proving several characteristic class formulae originally obtained by Cappell and Shaneson in the early 1990s.

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