Uniform measure equivalence invariance conjecture for L2L^2-torsion

Let GG and HH be countable groups such that all the L2L^2-Betti numbers of GG and HH vanish. Assume that both GG and HH admit finite CW-models for their classifying spaces. They satisfy the determinant conjecture. Two groups are measure equivalent with index c=I(G,H)>0c=I(G,H)>0 if they admit a measure coupling of that index. Uniform measure equivalence invariance conjecture. If GG and HH are measure equivalent with index cc, then

ρ(2)(G)=cρ(2)(H).\rho^{(2)}(G)=c\cdot\rho^{(2)}(H).

This conjecture predicts that L2L^2-torsion transforms proportionally under measure equivalence, analogously to the invariance of L2L^2-Betti numbers. The paper presents it as conjectural; the supplied text gives no resolution.

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Primary source

Wolfgang Lueck, Roman Sauer and Christian Wegner, “L2-torsion, the measure-theoretic determinant conjecture, and uniform measure equivalence”, arXiv:0903.2925 (2010).

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