MICROSCOPIC STRING ANALYSIS OF THE D0-D8 BRANE SYSTEM AND DUAL R-R STATES

Using the boundary state formalism, we perform a microscopic string an alysis of the interaction between two D-branes and provide a local int erpretation for the R-R force in the DO-Dg brane system. To do so, we construct BRST invariant vertex operators for the massless R-R states in the asymmetric picture that are proportional to potentials rather t han field strengths. The Hilbert space of such R-R states contains com binations of two vectors that decouple from all physical amplitudes, e ven in the presence of boundaries. Identifying these vectors, we remov e the null states and recover duality relations among R-R potentials. If we specify to the D0-D8 brane system, this mechanism implies that t he R-R I-form state has a non-zero overlap with both the D0-brane and the D8-brane, thus explaining from a local point of view the non-vanis hing R-R contribution in the interaction for the D0-D8 brane system an d those related to it by duality. (C) 1998 Elsevier Science B.V.