English

Comparison of component groups of $\ell$-adic and mod $\ell$ monodromy groups

Number Theory 2026-04-07 v2

Abstract

Let {ρ:GalKGLn(Q)}\{\rho_{\ell}:\mathrm{Gal}_K\to\mathrm{GL}_n(\mathbb{Q}_{\ell})\}_{\ell} be a semisimple compatible system of \ell-adic representations of a number field KK that is arising from geometry. Let GGLn,Q\textbf{G}_{\ell}\subset\mathrm{GL}_{n,\mathbb{Q}_{\ell}} and G^GLn,F\widehat{\underline{G_{\ell}}}\subset\mathrm{GL}_{n,\mathbb{F}_\ell} be respectively the algebraic monodromy group and full algebraic envelope of ρ\rho_{\ell}. We prove that there is a natural isomorphism between the component groups π0(G)π0(G^)\pi_0(\textbf{G}_{\ell}) \simeq \pi_0(\widehat{\underline{G_\ell}}) for all sufficiently large \ell.

Keywords

Cite

@article{arxiv.2407.20907,
  title  = {Comparison of component groups of $\ell$-adic and mod $\ell$ monodromy groups},
  author = {Boyi Dai and Chun Yin Hui},
  journal= {arXiv preprint arXiv:2407.20907},
  year   = {2026}
}

Comments

10 pages. To appear in Journal of Number Theory