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arXiv 1111.6951math.OAmath.DSmath.GR
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自由群任意作用下II_1因子的唯一Cartan分解

Unique Cartan decomposition for II_1 factors arising from arbitrary actions of free groups

Sorin Popa, Stefaan Vaes

摘要:

证明了对n个生成元\F_n,2 \leq n \leq \infty上的自由群的任意自由遍历概率测度保持作用\F_n \actson(X,μ),伴随群测度空间II_1因子$L^\infty(X) \rtimes \F_n$有L^ \infty(X)作为它的唯一Cartan子代数,直到酉共轭.我们证明了群测度空间II_1中由不同生成元个数的自由群作用所产生的因子是不同构的。我们实际上证明了唯一的Cartan分解结果II_1因子所产生的任意行动的一个相当大的家庭的群体,包括所有的自由积的顺从群体和他们的直积。

英文摘要:

We prove that for any free ergodic probability measure preserving action \F_n \actson (X,μ) of a free group on n generators \F_n, 2 \leq n \leq \infty, the associated group measure space II_1 factor $L^\infty(X) \rtimes \F_n$ has L^\infty(X) as its unique Cartan subalgebra, up to unitary conjugacy. We deduce that group measure space II_1 factors arising from actions of free groups with different number of generators are never isomorphic. We actually prove unique Cartan decomposition results for II_1 factors arising from arbitrary actions of a rather large family of groups, including all free products of amenable groups and their direct products.

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