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arXiv physics/9710005math-phhep-thmath.MPmath.QAq-alg
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非对易共形几何中的Moebius变换

Moebius Transformations in Noncommutative Conformal Geometry

Peter Bongaarts, Jacek Brodzki

摘要:

本文研究了任意代数A的投射线性群PGL_2(A)及其子群在A的对合空间上的作用。这种作用形式上类似于从复几何中已知的莫比乌斯变换。通过指定A是Hilbert空间H中的有界算子代数,重新发现了Connes定义的Moebius群,并研究了它在代数A上Fredholm模空间上的作用.在A的K-同调上存在一个诱导作用,它是平凡的。此外,这一行动自然会导致一个更简单的对象,极化模块的基础上一个给定的Fredholm模块,我们详细讨论这种关系。任何极化模都可以提升到Fredholm模,不同提升的集合形成一个范畴,其态射由广义Moebius变换给出。我们提出了一个例子的极化模块规范与可微结构的光滑流形V.使用我们的提升程序,我们得到了一类Fredholm模块的共形结构的特征V. Fredholm模块,以这种方式获得的是一个特殊情况下构造的Connes,Sullivan和Teleman。

英文摘要:

We study the projective linear group PGL_2(A), associated with an arbitrary algebra A, and its subgroups from the point of view of their action on the space of involutions in A. This action formally resembles Moebius transformations known from complex geometry. By specifying A to be an algebra of bounded operators in a Hilbert space H, we rediscover the Moebius group defined by Connes and study its action on the space of Fredholm modules over the algebra A. There is an induced action on the K-homology of A, which turns out to be trivial. Moreover, this action leads naturally to a simpler object, the polarized module underlying a given Fredholm module, and we discuss this relation in detail. Any polarized module can be lifted to a Fredholm module, and the set of different lifts forms a category, whose morphisms are given by generalized Moebius tranformations. We present an example of a polarized module canonically associated with the differentiable structure of a smooth manifold V. Using our lifting procedure we obtain a class of Fredholm modules characterizing the conformal structures on V. Fredholm modules obtained in this way are a special case of those constructed by Connes, Sullivan and Teleman.

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