English

Generic character sheaves on parahoric subgroups

Representation Theory 2025-08-12 v2 Algebraic Geometry

Abstract

We study parabolic induction producing \ell-adic sheaves on a parahoric subgroup scheme in the loop group of a reductive group. Under a genericity assumption on the input data, we prove that it produces conjugation equivariant perverse sheaves on the parahoric subgroup; this is upgraded to a tt-exact equivalence of categories of \ell-adic sheaves. An iterative version of the construction produces such a perverse sheaf starting from a geometric analogue of the data considered by J.-K. Yu and J. Kim. We prove, under a mild condition on qq, that generic parabolic induction from a parahoric torus realizes the character of the representation arising from the associated parahoric Deligne--Lusztig induction, which is known to parametrize the Fintzen--Kaletha--Spice twist of types. In the simplest interesting setting, our construction produces a simple perverse sheaf associated to a sufficiently nontrivial multiplicative local system on a torus, resolving a conjecture of Lusztig.

Keywords

Cite

@article{arxiv.2401.07189,
  title  = {Generic character sheaves on parahoric subgroups},
  author = {Roman Bezrukavnikov and Charlotte Chan},
  journal= {arXiv preprint arXiv:2401.07189},
  year   = {2025}
}

Comments

46 pages; v2: improved exposition, 49 pages

R2 v1 2026-06-28T14:16:09.717Z