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arXiv 0705.2578math.KTmath.GT
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低阶上同调的强Novikov猜想

The strong Novikov conjecture for low degree cohomology

Bernhard Hanke, Thomas Schick

摘要:

证明了对每个离散群G,有理装配映射K_*(BG)\to K_*(C*_{max} G)\otimes \Q在与次数至多为2的上同调类生成的子环对偶的类上是内射的(通过Chern特征标识别有理K-同调和同调).我们的结果意味着同伦不变性的更高的签名与这些上同调类。这一推论首先由Connes-Gromov-Moscovici和Mathai建立。我们的方法是基于平扭束的建设几乎平束的序列,首先在我们以前的工作。与Mathai的论点相反,我们的方法是独立的(并确实给出了一个新的证明)结果Hilsum Skandalis的同伦不变性的指数扭曲的签名运营商束的小曲率。

英文摘要:

We show that for each discrete group G, the rational assembly map K_*(BG) \otimes Q \to K_*(C*_{max} G) \otimes \Q is injective on classes dual to the subring generated by cohomology classes of degree at most 2 (identifying rational K-homology and homology via the Chern character). Our result implies homotopy invariance of higher signatures associated to these cohomology classes. This consequence was first established by Connes-Gromov-Moscovici and Mathai. Our approach is based on the construction of flat twisting bundles out of sequences of almost flat bundles as first described in our previous work. In contrast to the argument of Mathai, our approach is independent of (and indeed gives a new proof of) the result of Hilsum-Skandalis on the homotopy invariance of the index of the signature operator twisted with bundles of small curvature.

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