Frobenius actions on the de Rham cohomology of Drinfeld modules

Abstract

We study the action of endomorphisms of a Drinfeld A-module \phi on its de Rham cohomology H_{DR}(\phi,L) and related modules, in the case where \phi is defined over a field L of finite A-characteristic \mathfrak{p}. Among others, we find that the nilspace H_{0} of the total Frobenius Fr_{DR} on H_{DR}(\phi,L) \mathfrak{p} has dimension h = height of \phi. We define and study a pairing between the \mathfrak{p}-torsion _{\mathfrak{p}}\phi of \phi and H_{DR}(\phi,L), which becomes perfect after dividing out H_{0}.