
arXiv: 1402.5499
Let Γ \Gamma be a discrete group. Following Linnell and Schick one can define a continuous ring c ( Γ ) c(\Gamma ) associated with Γ \Gamma . They proved that if the Atiyah Conjecture holds for a torsion-free group Γ \Gamma , then c ( Γ ) c(\Gamma ) is a skew field. Also, if Γ \Gamma has torsion and the Strong Atiyah Conjecture holds for Γ \Gamma , then c ( Γ ) c(\Gamma ) is a matrix ring over a skew field. The simplest example when the Strong Atiyah Conjecture fails is the lamplighter group Γ = Z 2 ≀ Z \Gamma =\mathbb {Z}_2\wr \mathbb {Z} . It is known that C ( Z 2 ≀ Z ) \mathbb {C}(\mathbb {Z}_2\wr \mathbb {Z}) does not even have a classical ring of quotients. Our main result is that if H H is amenable, then c ( Z 2 ≀ H ) c(\mathbb {Z}_2\wr H) is isomorphic to a continuous ring constructed by John von Neumann in the 1930s.
QA Mathematics / matematika, von Neumann algebras, General theory of von Neumann algebras, lamplighter group, Mathematics - Rings and Algebras, Group Theory (math.GR), 16A30, continuous rings, 510, Rings and Algebras (math.RA), algebra of affiliated operators, FOS: Mathematics, Geometric group theory, Mathematics - Group Theory
QA Mathematics / matematika, von Neumann algebras, General theory of von Neumann algebras, lamplighter group, Mathematics - Rings and Algebras, Group Theory (math.GR), 16A30, continuous rings, 510, Rings and Algebras (math.RA), algebra of affiliated operators, FOS: Mathematics, Geometric group theory, Mathematics - Group Theory
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