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arXiv 0903.1741math.OAmath.DSmath.GN
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来自群作用的Hilbert C*-模:超越有限轨道情形

Hilbert C*-modules from group actions: beyond the finite orbits case

M. Frank, V. Manuilov, E. Troitsky

摘要:

研究了紧T2空间$X$上拓扑群的连续作用,这些作用在相应的交换C*-代数中诱导出殆周期函数。由平均得到的群上的唯一不变平均允许导出C* 值内积和Hilbert C* 模,其用作描述群作用的特性的环境。对于一致连续的,李雅普诺夫稳定的行动派生的不变平均$M(ϕ_x)$是连续的$X$的任何元素$ϕ\in C(X)$,和诱导的C* 值内积对应于一个条件期望从$C(X)$到不动点代数的行动定义的平均轨道。在希尔伯特C*-模的自对偶的情况下,所有的轨道都具有相同的基数。紧度量空间上的稳定作用产生C*-自反Hilbert C*-模。如果有限轨道的基数是一致有界的,无限轨道的闭包数是有限的,也是如此。一些例子说明了分类案件之外的典型情况。

英文摘要:

Continuous actions of topological groups on compact Hausdorff spaces $X$ are investigated which induce almost periodic functions in the corresponding commutative C*-algebra. The unique invariant mean on the group resulting from averaging allows to derive a C*-valued inner product and a Hilbert C*-module which serve as an environment to describe characteristics of the group action. For uniformly continuous, Lyapunov stable actions the derived invariant mean $M(ϕ_x)$ is continuous on $X$ for any element $ϕ\in C(X)$, and the induced C*-valued inner product corresponds to a conditional expectation from $C(X)$ onto the fixed point algebra of the action defined by averaging on orbits. In the case of selfduality of the Hilbert C*-module all orbits are shown to have the same cardinality. Stable actions on compact metric spaces give rise to C*-reflexive Hilbert C*-modules. The same is true if the cardinality of finite orbits is uniformly bounded and the number of closures of infinite orbits is finite. A number of examples illustrate typical situations appearing beyond the classified cases.

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