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arXiv 0709.0207math.RTmath.AG
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旗簇上的模交上同调复形

Modular intersection cohomology complexes on flag varieties

Geordie Williamson

摘要:

本文给出了一个组合方法(基于Coxeter群的W-图),证明了系数在任意域上的低秩复旗簇上的许多交上同调复形的特征由Kazhdan-Lusztig基元给出.我们的程序利用宇称层的存在性和唯一性。特别地,我们证明了在A_n型旗簇(n < 7)上的域中所有系数的交上同调复形的特征标都是由Kazhdan-Lusztig基元给出的.根据Soergel的结果,这暗示了Lusztig猜想的一部分,SL(n)的n \le 7。我们也给出了我们的技术失败的例子。在Tom Braden的附录中给出了SL(8)和SO(8)的旗变元上的交上同调复形的例子,它们的柄或余柄都有挠。

英文摘要:

We present a combinatorial procedure (based on the W-graph of the Coxeter group) which shows that the characters of many intersection cohomology complexes on low rank complex flag varieties with coefficients in an arbitrary field are given by Kazhdan-Lusztig basis elements. Our procedure exploits the existence and uniqueness of parity sheaves. In particular we are able to show that the characters of all intersection cohomology complexes with coefficients in a field on the flag variety of type A_n for n < 7 are given by Kazhdan-Lusztig basis elements. By results of Soergel, this implies a part of Lusztig's conjecture for SL(n) with n \le 7. We also give examples where our techniques fail. In the appendix by Tom Braden examples are given of intersection cohomology complexes on the flag varities for SL(8) and SO(8) which have torsion in their stalks or costalks.

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