On the Isomorphism of Semicircular Algebras
Abstract
Building on OpenAI's proof of isomorphism of free group factors, we give a self-contained proof of a corresponding result for C*-algebras generated by free semicircular systems: the isomorphism class of a C*-algebra generated by a semicircular n-tuple does not depend on n∈{2,3,…,+∞}. Similarly, reduced free products of n copies of the Jiang--Su algebra are isomorphic for different n in this range. While reduced free group C*-algebras of different ranks are not isomorphic (by a result of Pimsner--Voiculescu), we show that they have strong free absorption properties. At the heart of the proof is an automorphism approximation property for inclusions of C*- and W*-algebras; a relative version of that property was previously used to derive free complementation results.
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BibTeX
@misc{shlyakhtenko2026isomorphism,
title = {{On the Isomorphism of Semicircular Algebras}},
author = {D. Shlyakhtenko},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.19590},
eprint = {2610.19590},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.19590},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - On the Isomorphism of Semicircular Algebras
AU - D. Shlyakhtenko
PY - 2026
DA - 2026/10/14
PB - arXiv
DO - 10.48550/arxiv.2610.19590
UR - https://arxiv.org/abs/2610.19590
AB - Building on OpenAI's proof of isomorphism of free group factors, we give a self-contained proof of a corresponding result for C^*-algebras generated by free semicircular systems: the isomorphism class of a C^*-algebra generated by a semicircular n-tuple does not depend on n∈{2,3,…,+∞}. Similarly, reduced free products of n copies of the Jiang--Su algebra are isomorphic for different n in this range. While reduced free group C^*-algebras of different ranks are not isomorphic (by a result of Pimsner--Voiculescu), we show that they have strong free absorption properties. At the heart of the proof is an automorphism approximation property for inclusions of C^*- and W^*-algebras; a relative version of that property was previously used to derive free complementation results.
ER -