Universal Chern classes on the moduli of bundles

Abstract

The goal of this paper is to construct universal cohomology classes on the moduli space of stable bundles over a curve when it is not a fine moduli space, i.e. when the rank and degree are not coprime. More precisely, we show that certain Chern classes of the universal bundle on the product of the curve with the moduli stack of bundles lift to the product of the curve with the moduli space of stable bundles.