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arXiv 1006.5378math.OAmath.RA
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群代数的Connes嵌入与von Neumann正则闭包

Connes Embeddings and von Neumann Regular Closures of Group Algebras

Gabor Elek

摘要:

Linnell和Schick引入了复群代数$\CΓ$的解析von Neumann正则闭包$R(Γ)$.这个环是包含$\CΓ$的附属算子代数$U(Γ)$中最小的$*$ -正则子环.证明了顺从群的sofic表示所对应的代数vonNeumann正则闭包同构于$R(Γ)$ .这个结果可以看作是Lück逼近定理的结构推广。\noindent证明的主要工具可能是独立的兴趣是,一个顺从的群代数$KΓ$在任何领域$K$可以嵌入到超矩阵代数的秩完成。

英文摘要:

The analytic von Neumann regular closure $R(Γ)$ of a complex group algebra $\CΓ$ was introduced by Linnell and Schick. This ring is the smallest $*$-regular subring in the algebra of affiliated operators $U(Γ)$ containing $\CΓ$. We prove that all the algebraic von Neumann regular closures corresponding to sofic representations of an amenable group are isomorphic to $R(Γ)$. This result can be viewed as a structural generalization of Lück's Approximation Theorem. \noindent The main tool of the proof which might be of independent interest is that an amenable group algebra $KΓ$ over any field $K$ can be embedded to the rank completion of an ultramatricial algebra.

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