English

Calculations with graded perverse-coherent sheaves

Representation Theory 2019-03-11 v2

Abstract

In this paper, we carry out several computations involving graded (or Gm\mathbb{G}_{\mathrm{m}}-equivariant) perverse-coherent sheaves on the nilpotent cone of a reductive group in good characteristic. In the first part of the paper, we compute the weight of the Gm\mathbb{G}_{\mathrm{m}}-action on certain normalized (or "canonical") simple objects, confirming an old prediction of Ostrik. In the second part of the paper, we explicitly describe all simple perverse coherent sheaves for G=PGL3G = PGL_3, in every characteristic other than 2 or 3. Applications include an explicit description of the cohomology of tilting modules for the corresponding quantum group, as well as a proof that PCohGm(N)\mathsf{PCoh}^{\mathbb{G}_{\mathrm{m}}}(\mathcal{N}) never admits a positive grading when the characteristic of the field is greater than 3.

Keywords

Cite

@article{arxiv.1806.07780,
  title  = {Calculations with graded perverse-coherent sheaves},
  author = {Pramod N. Achar and William D. Hardesty},
  journal= {arXiv preprint arXiv:1806.07780},
  year   = {2019}
}

Comments

23 pages. v2: minor corrections

R2 v1 2026-06-23T02:36:07.170Z