Evidence for a generalization of Gieseker's conjecture on stratified bundles in positive characteristic

Abstract

Let X be a smooth, connected, projective variety over an algebraically closed field of positive characteristic. In "Flat vector bundles and the fundamental group in non-zero characteristics" (Ann. Scuola Norm. Sup. Pisa Cl. Sci. (4) 2 (1975)), Gieseker conjectured that every stratified bundle (i.e. every O-coherent D-module) on X is trivial, if and only if the étale fundamental group of X is trivial. This was proven by Esnault-Mehta in "Simply connected projective manifolds in characteristic p> 0 have no nontrivial stratified bundles" (Invent. Math. 181 (2010)). Building on the classical situation over the complex numbers, we present and motivate a generalization of Gieseker's conjecture using the notion of regular singular stratified bundles developed in the author's thesis and arXiv:1210.5077. In the main part of this article we establish some important special cases of this generalization; most notably we prove that for not necessarily proper X, the vanishing of the tame fundamental group of X implies that there are no nontrivial regular singular stratified bundles with abelian monodromy.