Coherence conjecture for finite-type RFRS groups

Let GG be a RFRS group of type FP\mathrm{FP}. A group is coherent if every finitely generated subgroup is finitely presented. The algebra Q[G]\mathbb{Q}[G] is the rational group algebra, and U(G)\mathcal U(G) is the algebra of operators affiliated to the group von Neumann algebra of GG. Coherence conjecture for finite-type RFRS groups. The following are equivalent:

(i)G is coherent;(ii)Q[G] is coherent;(iii)U(G) is of weak dimension one as a Q[G]-module.\begin{array}{ll} \text{(i)} & G\text{ is coherent};\\ \text{(ii)} & \mathbb{Q}[G]\text{ is coherent};\\ \text{(iii)} & \mathcal U(G)\text{ is of weak dimension one as a }\mathbb{Q}[G]\text{-module}. \end{array}

This prediction concerns coherence for RFRS groups of finite type and connects it to the weak dimension of the affiliated-operator algebra. The source presents it as a prediction and gives no resolution.

Sources & referencesView supporting material

Primary source

Sam P. Fisher, “Novikov cohomology, finite domination, and cohomological dimension”, arXiv:2510.14796 (2025).

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