The conjecture that the first L2L^2-Betti numbers agree over the von Neumann algebra and division ring

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Let GG be a finitely presented group and let FF be a field. Denote by b1(2)(G;N(G))b^{(2)}_1(G;\mathcal N(G)) the first L2L^2-Betti number with coefficients in the group von Neumann algebra, and by b1(2)(G;DFG)b^{(2)}_1(G;\mathcal D_{FG}) the corresponding invariant with coefficients in the division ring DFG\mathcal D_{FG}. First L2L^2-Betti-number equality conjecture. The equality

b1(2)(G;N(G))=b1(2)(G;DFG)b^{(2)}_1(G;\mathcal N(G))=b^{(2)}_1(G;\mathcal D_{FG})

holds for all finitely presented groups GG and every field FF.

This conjecture compares characteristic-independent von Neumann-algebra invariants with division-ring versions over arbitrary fields. No resolution is given in the supplied source.

References

Primary source

Grigori Avramidi and Wolfgang Lueck, “L^2-Betti numbers in prime characteristic and a conjecture of Wise”, arXiv:2602.04655 (2026).

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