Published online by Cambridge University Press: 01 December 2023
We prove a Tannakian form of Drinfeld's lemma for isocrystals on a variety over a finite field, equipped with actions of partial Frobenius operators. This provides an intermediate step towards transferring V. Lafforgue's work on the Langlands correspondence over function fields from $\ell$-adic to
$p$-adic coefficients. We also discuss a motivic variant and a local variant of Drinfeld's lemma.
The first author is supported by NSF grants DMS-1802161 and DMS-2053473 and the UC San Diego Warschawski Professorship. The second author is supported by the National Natural Science Foundation of China grants 12222118 and 12288201 and the CAS Project for Young Scientists in Basic Research grant YSBR-033. D.X. is grateful to Xinwen Zhu for suggesting this question and helpful discussions.