The folk conjecture on von Neumann subalgebras of uniform Roe and quasi-local algebras

From papers

Let XX be an infinite uniformly locally finite metric space. A von Neumann algebra is said to embed into an associated uniform Roe algebra or quasi-local algebra if it admits an injective *-homomorphism into that algebra. For a countable collection of natural numbers (nk)k(n_k)_k, write kMnk(C)\prod_k \mathrm{M}_{n_k}(\mathbb{C}) for the corresponding von Neumann algebra.

Folk conjecture. The only von Neumann algebras that can embed into a uniform Roe algebra or a quasi-local algebra associated to a uniformly locally finite metric space are those of the form

kMnk(C),\prod_k \mathrm{M}_{n_k}(\mathbb{C}),

where (nk)k(n_k)_k is a countable, possibly finite, bounded collection of natural numbers.

The conjecture concerns the possible von Neumann algebra subalgebras of uniform Roe and quasi-local algebras; the paper subsequently gives a more precise refinement. Its resolution is not specified in the supplied text.

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Primary source

Florent P. Baudier, Bruno de Mendonça Braga, Ilijas Farah, Alessandro Vignati and Rufus Willett, “Embeddings of von Neumann algebras into uniform Roe algebras and quasi-local algebras”, arXiv:2212.14312 (2023).

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