A Hitchin-Kobayashi Correspondence for Coherent Systems on Riemann Surfaces

A `coherent system' $(\Cal E,V)$, consists of a holomorphic bundle plus a linear subspace of its space of holomorphic sections. Based on the usual notion in Geometric Invariant Theory, a notion of slope stability has been defined for such objects (by Le Potier, and also by Rhagavendra and Vishwanath). In this paper we show that stability in this sense is equivalent to the existence of solutions to a certain set of gauge theoretic equations. One of the equations is essentially the vortex equation (i.e. the Hermitian-Einstein equation with an additional zeroth order term), and the other is an orthonormality condition on a frame for the subspace $V\subset H^0(\Cal E)$.