Abelian Subalgebras of Von Neumann Algebras from Flat Tori in Locally Symmetric Spaces
نویسنده
چکیده
Consider a compact locally symmetric space M of rank r, with fundamental group Γ. The von Neumann algebra VN(Γ) is the convolution algebra of functions f ∈ l2(Γ) which act by left convolution on l2(Γ). Let T r be a totally geodesic flat torus of dimension r in M and let Γ0 ∼= Z r be the image of the fundamental group of T r in Γ. Then VN(Γ0) is a maximal abelian ⋆-subalgebra of VN(Γ) and its unitary normalizer is as small as possible. If M has constant negative curvature then the Pukánszky invariant of VN(Γ0) is ∞.
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