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Symmetric Branching via Laurent Phenomenon Algebras

Abstract

We construct Laurent phenomenon structures on reductive branching algebras. For A2n−1↓ Cn, n≥ 2, and the exceptional inclusions D4↓ G2, E6↓ F4, and F4↓ B4, we identify the branching algebras with upper Laurent phenomenon algebras, keeping the frozen coefficients polynomial. Degree-fibred categories of projective presentations give a common construction. It also gives cluster seeds of type A1 for B3 ↓ G2 and G2↓ A2. We give uniform sufficient conditions identifying a specialized Keel--Yu mirror algebra with an upper Laurent phenomenon algebra admitting a suitable binomial seed. The resulting theta basis is simultaneously adapted to the frozen boundary valuations. For A2n−1↓ Cn with 2≤ n≤5 and for the other exceptional inclusions, we obtain homogeneous theta bases parametrized by lattice points of explicit rational polyhedral cones, whose weight fibres compute every branching multiplicity. We also prove mutation invariance of finite upper bounds for LP patterns over a UFD.

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BibTeX
@misc{fei2026symmetric,
  title = {{Symmetric Branching via Laurent Phenomenon Algebras}},
  author = {Jiarui Fei},
  howpublished = {arXiv},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2609.32425},
  eprint = {2609.32425},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2609.32425},
}
RIS
TY  - UNPB
TI  - Symmetric Branching via Laurent Phenomenon Algebras
AU  - Jiarui Fei
PY  - 2026
DA  - 2026/09/26
PB  - arXiv
DO  - 10.48550/arxiv.2609.32425
UR  - https://arxiv.org/abs/2609.32425
AB  - We construct Laurent phenomenon structures on reductive branching algebras. For A_2n−1↓ C_n, n≥ 2, and the exceptional inclusions D_4↓ G_2, E_6↓ F_4, and F_4↓ B_4, we identify the branching algebras with upper Laurent phenomenon algebras, keeping the frozen coefficients polynomial. Degree-fibred categories of projective presentations give a common construction. It also gives cluster seeds of type A_1 for B_3 ↓ G_2 and G_2↓ A_2. We give uniform sufficient conditions identifying a specialized Keel--Yu mirror algebra with an upper Laurent phenomenon algebra admitting a suitable binomial seed. The resulting theta basis is simultaneously adapted to the frozen boundary valuations. For A_2n−1↓ C_n with 2≤ n≤5 and for the other exceptional inclusions, we obtain homogeneous theta bases parametrized by lattice points of explicit rational polyhedral cones, whose weight fibres compute every branching multiplicity. We also prove mutation invariance of finite upper bounds for LP patterns over a UFD.
ER  -