A Compactification Over $\overline{M}_g$ Of The Universal Moduli Space of Slope-Semistable Vector Bundles

A projective moduli space of pairs (C,E) where E is a slope- semistable torsion free sheaf of uniform rank on a Deligne- Mumford stable curve C is constructed via G.I.T. There is a natural SL x SL action on the relative Quot scheme over the universal curve of the Hilbert scheme of pluricanonical, genus g curves. The G.I.T. quotient of this product action yields a functorial, compact solution to the moduli problem of pairs (C,E). Basic properties of the moduli space are studied. An alternative approach to the moduli problem of pairs has been suggested by D. Gieseker and I Morrison and completed by L. Caporaso in the rank 1 case. It is shown the contruction given here is isomorphic to Caporaso's compactification in the rank 1 case.