Boundary string field theory of the DD system -: art. no. 106004

We develop the boundary string field theory approach to tachyon condensation on the D (D) over bar system. Particular attention is paid to the gauge fields, which combine with the tachyons in a natural way. We derive the RR couplings of the system and express the result in terms of Quillen's superconnection. The result is related to an index theorem, and is thus shown to be exact.