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

We develop the boundary string field theory approach to tachyon condensatio n on the D (D) over bar system. Particular attention is paid to the gauge f ields, which combine with the tachyons in a natural way. We derive the RR c ouplings of the system and express the result in terms of Quillen's superco nnection. The result is related to an index theorem, and is thus shown to b e exact.