English

Permutation twisted cohomology, remixed

Representation Theory 2026-02-10 v3 Algebraic Geometry Category Theory Group Theory

Abstract

For each endotrivial complex arising from Bredon homology of a representation sphere, we construct pp-local quasi-isomorphisms, called forerunners, enabling us to extend Balmer--Gallauer's results in arXiv:2307.04398 Part II concerning the tensor-triangular geometry of permutation modules for elementary abelian pp-groups to all pp-groups. We construct an open cover of the Balmer spectrum under which all endotrivials are line bundles, that is, every endotrivial is locally isomorphic to a shifted tensor unit. We define a 'remixed' permutation twisted cohomology ring for which the canonical comparison map from the Balmer spectrum to the homogeneous spectrum of the twisted cohomology ring is injective. If the twisted cohomology ring is Noetherian, the comparison map is an open immersion, and the open cover endows the Balmer spectrum with Dirac scheme structure. We prove Noetherianity holds for Dedekind groups and all pp-groups of order at most p3p^3, and conjecture Noetherianity holds for all finite pp-groups.

Keywords

Cite

@article{arxiv.2509.00954,
  title  = {Permutation twisted cohomology, remixed},
  author = {Sam K. Miller},
  journal= {arXiv preprint arXiv:2509.00954},
  year   = {2026}
}

Comments

v3: Major update, significant rewrite. A new section in which we deduce Noetherianity for Dedekind p-groups and p-groups of order at most p^3 is included. We conjecture that Noetherianity holds in general. 50 pages, submitted version

R2 v1 2026-07-01T05:14:18.769Z