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Large profinite genus and extensions in Bestvina-Brady groups

Abstract

We construct the first examples of uncountable families of residually finite duality groups of type FP, all of which have isomorphic profinite completions, while being pairwise not quasi-isometric. To establish these finiteness properties, we prove conjectures of Leary regarding groups of deck transformations of certain cubical branched covers being residually finite and virtually special. The main new tool is a strong separability result for Bestvina-Brady groups, allowing the extension of any finite quotient of many Bestvina-Brady subgroups to a finite quotient of the whole group. This gives a finite version of the congruence extension property, which we also establish for the same group pairs.

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BibTeX
@misc{vankov2026large,
  title = {{Large profinite genus and extensions in Bestvina-Brady groups}},
  author = {Vladimir Vankov},
  howpublished = {arXiv},
  year = {2026},
  month = oct,
  doi = {10.48550/arxiv.2610.32775},
  eprint = {2610.32775},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2610.32775},
}
RIS
TY  - UNPB
TI  - Large profinite genus and extensions in Bestvina-Brady groups
AU  - Vladimir Vankov
PY  - 2026
DA  - 2026/10/23
PB  - arXiv
DO  - 10.48550/arxiv.2610.32775
UR  - https://arxiv.org/abs/2610.32775
AB  - We construct the first examples of uncountable families of residually finite duality groups of type FP, all of which have isomorphic profinite completions, while being pairwise not quasi-isometric. To establish these finiteness properties, we prove conjectures of Leary regarding groups of deck transformations of certain cubical branched covers being residually finite and virtually special. The main new tool is a strong separability result for Bestvina-Brady groups, allowing the extension of any finite quotient of many Bestvina-Brady subgroups to a finite quotient of the whole group. This gives a finite version of the congruence extension property, which we also establish for the same group pairs.
ER  -