Supergravity Approach to Tachyon Potential in Brane-Antibrane Systems

Using an exact supergravity solution representing the Dp-\bar{Dp} system, it is demonstrated that one can construct a supergravity analogue of the tachyon potential. Remarkably, the (regularized) minimum value of the potential turns out to be V(T_{0})=-2m with m denoting the ADM mass of a single Dp-brane. This result, in a sense, appears to confirm that Sen's conjecture for the tachyon condensation on unstable D-branes is indeed correct although the analysis used here is semi-classical in nature and hence should be taken with some care. Also shown is the fact that the tachyon mass squared m^2_{T} (which has started out as being negative) can actually become positive definite and large as the tachyon rolls down toward the minimum of its potential. It indeed signals the possibility of successful condensation of the tachyon since it shows that near the minimum of its potential, tachyon can become heavy enough to disappear from the massless spectrum. Some cosmological implications of this tachyon potential in the context of ``rolling tachyons'' is also discussed.