First-order free group factor alternative

From papers

For r(1,]r\in(1,\infty], let L(Fr)L(\mathbb F_r) be the interpolated free group factor, and let the first-order fundamental group of L(Fr)L(\mathbb F_r) be the group of positive scalars tt such that the amplification of L(Fr)L(\mathbb F_r) by tt is elementarily equivalent to L(Fr)L(\mathbb F_r). Let \equiv denote elementary equivalence. First-order free group factor alternative. One of the following two statements must hold:

  1. L(Fr)L(Fs)L(\mathbb F_r)\equiv L(\mathbb F_s) for all 1<rs1<r\leq s\leq\infty, and the first-order fundamental group of L(Fr)L(\mathbb F_r) is R+\mathbb R_+ for all 1<r1<r\leq\infty.
  2. L(Fr)≢L(Fs)L(\mathbb F_r)\not\equiv L(\mathbb F_s) for all 1<r<s1<r<s\leq\infty, and the first-order fundamental group of L(Fr)L(\mathbb F_r) is {1}\{1\} for all 1<r<1<r<\infty.

This is the proposed analogue for first-order elementary equivalence of the free group factor alternative. The source presents it as conjectural and does not state that either alternative has been established.

Progress summary

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Sources & referencesView supporting material

Primary source

Isaac Goldbring and Jennifer Pi, “On the First-Order Free Group Factor Alternative”, arXiv:2305.08168 (2025).

Additional references

4 papers in this index state this conjecture (2016–2023). The statement above is taken from the most recent of them; the others are arXiv:2109.13133, arXiv:2010.07970, arXiv:1606.04642.

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