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Depth of free-by-cyclic groups

Abstract

For a free group automorphism, we prove that its poset of attracting lamination orbits is a canonical invariant of the associated mapping torus. That is, if a free-by-cyclic group splits as a mapping torus in two different ways, then the corresponding automorphisms have isomorphic posets of lamination orbits. Further, we show that the lamination depth, the size of the largest chain in this poset, is a commensurability invariant of the free-by-cyclic group.

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BibTeX
@misc{dowdall2026depth,
  title = {{Depth of free-by-cyclic groups}},
  author = {Spencer Dowdall and Yassine Guerch and Radhika Gupta and Jean Pierre Mutanguha and Caglar Uyanik},
  howpublished = {HAL},
  year = {2026},
  month = oct,
  doi = {10.48550/arxiv.2602.10433},
  eprint = {2602.10433},
  archivePrefix = {arXiv},
  url = {https://hal.science/hal-05798895v1},
  note = {CC BY},
}
RIS
TY  - UNPB
TI  - Depth of free-by-cyclic groups
AU  - Spencer Dowdall
AU  - Yassine Guerch
AU  - Radhika Gupta
AU  - Jean Pierre Mutanguha
AU  - Caglar Uyanik
PY  - 2026
DA  - 2026/10/14
PB  - HAL
DO  - 10.48550/arxiv.2602.10433
UR  - https://hal.science/hal-05798895v1
AB  - For a free group automorphism, we prove that its poset of attracting lamination orbits is a canonical invariant of the associated mapping torus. That is, if a free-by-cyclic group splits as a mapping torus in two different ways, then the corresponding automorphisms have isomorphic posets of lamination orbits. Further, we show that the lamination depth, the size of the largest chain in this poset, is a commensurability invariant of the free-by-cyclic group.
ER  -