1. Nonhyperlinear groups exist PDFA complete draft of this result, verified by humans, is now on arXiv: Vadim Alekseev, Jihao Liu, Andreas Thom, Spectral gap, internality of relative commutants, and non-hyperlinear groups, arXiv:2609.37761. The credit for the result goes to that paper. The PDF below is kept only as a historical reference, and this entry will not be updated any further.
Jihao Liu
AI-generated paper · proof accepted by the Danus verifier 2026-09-19 22:29:37 UTC · posted here 2026-09-20 06:24:54 UTC · not submitted to arXiv; superseded by
arXiv:2609.37761
This paper constructs a countable discrete group that is not hyperlinear. Equivalently,
its group von Neumann algebra, with its canonical trace, does not embed into an
ultrapower of the hyperfinite II1 factor, so Connes’ embedding problem
has a negative answer for groups. The group is the generalized wreath product
W = (⊕G/Γ Z/2) ⋊ G,
where Γ = EL3(F2[x1,
x2, x3]) and
G = EL3(F2[x1±1,
x2±1, x3±1]) ⋊ SL3(Z).
It is one of the groups that Kun and Thom
(arXiv:2608.06222) proved to be nonsofic,
building on the first nonsofic group, found by
OpenAI.
The new ingredient is a theorem on tracial ultraproducts of matrix algebras: the
relative commutant of a finitely generated Kazhdan group in such an ultraproduct is
itself an ultraproduct of finite-dimensional subalgebras of the same matrix algebras
(Theorem 1.2 of the paper). This is a positive answer to the centralizer
problem, that is, Open Problem 6.2(a) of Alekseev and Thom
(arXiv:2608.05362). The second step of
the argument (Theorem 1.3 of the paper: a Kazhdan group generated by a subgroup
together with finitely many elements that conjugate this subgroup into itself
normalizes the relative commutant of the subgroup) was proved earlier by Andreas Thom,
conditionally on the centralizer problem, in his preprint
A conditional
construction of a nonhyperlinear group and the centralizer problem; the credit
for it belongs to him (see the update of 20 September below). Danus ran with
seven proof workers and found the proof in 7 hours and 11 minutes.
Disclaimer: This is an AI-generated manuscript. The proof has been
checked by machines (the internal verifier of Danus, and an independent line-by-line AI
review that found no invalid inference), but it has not been verified by a human.
Readers should independently check every mathematical claim before relying on or citing
it.
Update (2026-09-20 08:07:35 UTC): the PDF was replaced. The introduction now cites
OpenAI’s construction of the first nonsofic group, on whose compression criterion
the work of Kun and Thom and this paper build; the mathematics is unchanged.
Update (2026-09-20 11:19:40 UTC): prior work of Andreas Thom. On 20 September 2026,
after this paper had been posted here, Andreas Thom informed me of his preprint
A conditional
construction of a nonhyperlinear group and the centralizer problem. According
to him, a first version was circulated on 10 August 2026 and submitted to arXiv on
17 August 2026, where it has been on hold; it has been publicly available on his
homepage since 25 August 2026. His paper shows that a positive answer to the
centralizer problem implies the normalization statement (his Theorem 1.2) and
hence, conditionally, that the group doubles G ∗H G
of the Kun–Thom pairs are not hyperlinear (his Theorem 1.3).
Theorem 1.3 of my paper overlaps with his Theorem 1.2, which has
priority: the credit for it belongs to Thom. I was not aware of his preprint.
The sources recorded during the Danus run do not contain it, but it was available
online, and I cannot guarantee that the AI models involved had not come across it.
What my paper contributes is Theorem 1.2, a positive answer to the centralizer
problem; combined with Thom’s Theorem 1.3 it also shows unconditionally that
those group doubles are not hyperlinear. The PDF was replaced: its introduction now
states all of this and cites Thom’s preprint.
Update (2026-09-21 08:27:54 UTC): MIP* = RE and orthogonalization results.
Mikael de la Salle pointed out that the paper gave no credit to two bodies of earlier
work; the PDF was replaced and now does. First, the statement is equivalent to the
existence of a group von Neumann algebra that does not embed into
Rω. The first tracial von Neumann algebras that do not embed
into Rω are due to Ji, Natarajan, Vidick, Wright and Yuen
(MIP* = RE); what my paper adds
is that one can take the von Neumann algebra of a group, with a proof that does not use
MIP* = RE. Second, Theorem 4.3 (rounding an operator-valued partition to a
projection-valued one) belongs to the line of orthogonalization results of
Kempe–Vidick, of Ji–Natarajan–Vidick–Wright–Yuen, and of
de la Salle (Orthogonalization of
positive operator valued measures, C. R. Math. 2022). The distance
estimate of Theorem 4.3 is de la Salle’s Theorem 2 with a worse
constant, and its proof follows his strategy; the new part is the simultaneous
control of the commutator energy, uniformly in the number of outcomes and in the
dimension. The sources recorded during the Danus run do contain de la Salle’s
paper; the first version of the manuscript omitted the reference. The introduction
(the paragraphs on Connes’ embedding problem and “Relation to
orthogonalization results”) and the beginning of Section 4 now state this, and
nine references were added. The acknowledgements of the paper now thank Mikael de la Salle and Andreas Thom.
Update (2026-09-25 08:36:42 UTC): joint paper with Vadim Alekseev and Andreas Thom.
I am now collaborating with Vadim Alekseev and Andreas Thom on a much better written
paper. We have isolated the core strategy of the proof and put the ideas into a
self-contained note which, together with Thom’s preprint
A conditional construction of a
nonhyperlinear group and the centralizer problem (arXiv:2609.27795), proves the
existence of a nonhyperlinear group. The PDF posted here will in principle not be changed
any further; it is kept as a historical record.
Update (2026-10-06 21:13:41 UTC): the human-verified paper is on arXiv.
The joint paper with Vadim Alekseev and Andreas Thom announced in the previous update is
now on arXiv: Spectral gap, internality of relative commutants, and non-hyperlinear
groups, arXiv:2609.37761 (posted
29 September 2026; no. 75 in my
list of publications). It is a complete draft,
verified by humans, and it supersedes the manuscript posted here: the credit for the
existence of a non-hyperlinear group goes to that paper. The PDF on this page is kept
only as a historical reference, and this entry will not be updated after this note.