Unique Cartan decomposition for II1 factors arising from arbitrary actions of free groups
Abstract
We prove that for any free ergodic probability measure preserving action n (X,μ) of a free group on n generators n, 2 ≤ n ≤ ∞, the associated group measure space II1 factor L∞(X) n has L∞(X) as its unique Cartan subalgebra, up to unitary conjugacy. We deduce that group measure space II1 factors arising from actions of free groups with different number of generators are never isomorphic. We actually prove unique Cartan decomposition results for II1 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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