Do the group factors of PSLₙ(ℤ) remember n?
Problem. Let $m, n \ge 3$. Does $L(\mathrm{PSL}_m(\mathbb Z)) \cong L(\mathrm{PSL}_n(\mathbb Z))$ imply $m = n$?
Source: S. Popa, Some open problems in W*-rigidity (2013), as a case of Connes's rigidity conjecture; listed as R.4 in J. Peterson, Open problems in operator algebras (version of 15 May 2026).
Imported from math.uwaterloo.ca/~j37peter/problems.html.
Classification
- Primary
- OA — Operator Algebras
- Secondary
- GR
- Keywords
- group von Neumann algebras, lattices in Lie groups, Peterson's operator algebra problems, W*-rigidity
References
@misc{popa2013problems-r4,
author = {Popa, Sorin},
title = {Some open problems in {W}$^*$-rigidity},
howpublished = {Slides, Paris, June 2013},
year = {2013},
url = {https://www.math.ucla.edu/~popa/ProblemsJune2013.pdf},
}
@misc{peterson-r4,
author = {Peterson, Jesse},
title = {Open problems in operator algebras},
howpublished = {Web page},
year = {2026},
url = {https://www.math.uwaterloo.ca/~j37peter/problems.html},
note = {Problem R.4; version of 15 May 2026},
}
@article{cowling1989-r4,
author = {Cowling, Michael and Haagerup, Uffe},
title = {Completely bounded multipliers of the {F}ourier algebra of a simple {L}ie group of real rank one},
journal = {Invent. Math.},
volume = {96},
number = {3},
pages = {507--549},
year = {1989},
doi = {10.1007/BF01393695},
}
@article{connesjones1985,
author = {Connes, Alain and Jones, Vaughan},
title = {Property {T} for von {N}eumann algebras},
journal = {Bull. Lond. Math. Soc.},
volume = {17},
number = {1},
pages = {57--62},
year = {1985},
doi = {10.1112/blms/17.1.57},
}
Resolution claims
We prove stable canonical recovery for scalar-twisted group factors of ICC groups commensurable with property-$(T)$ lattices over characteristic-zero local fields. Every specified stable isomorphism to a scalar-twisted factor of any countably infinite ICC group recovers the group, the cocycle up to a normalized cochain, and equal amplification scales, with an implementing partial isometry in the given matrix corners. We compute …
Status history
| When | Change | By | Reason |
|---|---|---|---|
| 2026-10-29 | Needs verification → Solution claimed | — | Recorded here: math @ 7ef5c0c, build/paper.tex. |
Citing this problem
This identifier is permanent. It will not change if the problem is solved, reclassified or withdrawn.
OP-01058, "Do the group factors of PSLₙ(ℤ) remember n?", clopen.solutions.