English

Rank 2 local systems and abelian varieties

Algebraic Geometry 2021-06-25 v4 Number Theory

Abstract

Let X/FqX/\mathbb{F}_{q} be a smooth geometrically connected variety. Inspired by work of Corlette-Simpson over C\mathbb{C}, we formulate a conjecture that absolutely irreducible rank 2 local systems with infinite monodromy on XX come from families of abelian varieties. When XX is a projective variety, we prove a Lefschetz-style theorem for abelian schemes of GL2\text{GL}_2-type on XX, modeled after a theorem of Simpson. If one assumes a strong form of Deligne's (pp-adic) \emph{companions conjecture} from Weil II, this implies that our conjecture for projective varieties also reduces to the case of projective curves. We also answer affirmitavely a question of Grothendieck on extending abelian schemes via their pp-divisible groups.

Keywords

Cite

@article{arxiv.1809.02106,
  title  = {Rank 2 local systems and abelian varieties},
  author = {Raju Krishnamoorthy and Ambrus Pál},
  journal= {arXiv preprint arXiv:1809.02106},
  year   = {2021}
}

Comments

29 pages, comments very welcome. v3: completely reorganized, minor errors fixed. v4: final version

R2 v1 2026-06-23T03:56:59.746Z