Supergravity approach to tachyon condensation on the brane-antibrane system

We study the tachyon condensation on the D-brane--antiD-brane system from the supergravity point of view. The non-supersymmetric supergravity solutions with symmetry ISO($p,1$) $\times$ SO($9-p$) are known to be characterized by three parameters. By interpreting this solution as coincident $N$ D$p$-branes and ${\bar N}$ ${\bar {\rm D}}p$-branes we give, for the first time, an explicit representation of the three parameters of supergravity solutions in terms of $N, \bar N$ and the tachyon vev. We demonstrate that the solution and the corresponding ADM mass capture all the required properties and give a correct description of the tachyon condensation advocated by Sen on the D-brane--antiD-brane system.