On brane antibrane forces

In this note, we will discuss two aspects of brane-antibrane forces. In one aspect, we generalize the force calculation of D0-bar D0 of Banks and Susskind to Dp-bar Dp for 1 <= p <= 8. In particular, we find that the force is also divergent for p = 1 while for the other cases (p >= 2) the forces are in general finite when Z → 0⁺, where Z = (Y²)/(2π²α')-1 with Y, the brane-antibrane separation. However, the forces are divergent for all cases when Z < 0, signalling the occurrence of open string tachyon condensation in this regime. The other deals with the puzzling static nature of the supergravity brane-antibrane configurations. We will show that the force on a brane probe due to a brane-antibrane background vanishes when the probe is placed at the location of the coincident brane-antibranes, thereby providing a direct evidence for the existence of general static brane-antibrane configuration in the supergravity approximation.