Gournay dimension-zero characterization by invariant exhaustions

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Let GG be a countable discrete amenable group, let 1≤p<∞1\leq p<\infty, and let F⊆ℓpGF\subseteq \ell^pG be a closed invariant subspace. An invariant exhaustion (Ei)i(E_i)_i of ℓpG\ell^pG is an exhaustion by invariant subspaces, and dim⁡ℓpF\dim_{\ell^p}F denotes the ℓp\ell^p-dimension of FF.

Gournay's dimension-zero conjecture. One has

dim⁡ℓpF=0\dim_{\ell^p}F=0

if and only if there is an invariant exhaustion (Ei)i(E_i)_i of ℓpG\ell^pG such that

Ei∩F=0E_i\cap F=0

for all ii.

The paper notes that the existence of such an exhaustion implies dim⁡ℓpF=0\dim_{\ell^p}F=0 for amenable groups and conjectures the converse. The analogous question can also be considered for sofic groups; the source does not provide a resolution.

References

Primary source

Nicolas Monod and Henrik Densing Petersen, “An obstruction to ^p-dimension”, arXiv:1207.1199 (2012).

Additional references

2 papers in this index state this conjecture (2011–2012). The statement above is taken from the most recent of them; the others are arXiv:1110.5390.

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