Bound states and brane annihilation in 11 D SUGRA

We study scattering of $D0$ branes in eleven dimensional supergravity (SUGRA) using the tree level four point amplitude. The range of validity of SUGRA allows us to make reliable calculations of relativistic brane scattering, inaccessible in string theory because of halo effects. We also compare the rate of annihilation of $D0-\bar{D0}$ branes to the rate of elastic $D0-\bar{D0}$ scattering and find that the former is always smaller than the latter. We also find a pole in $\sigma_{D0-\bar{D0}}$. We exploit the analogy with the positronium to argue that the brane anti-brane pairs form branium atoms in 3 spatial dimensions. We also derive a long range effective potential for interacting branes which explicitly depends on their polarizations. We compare two approaches to large impact parameter brane scattering: in GR, polarizations of the branes are kept constant during the interaction, while in QFT, one sums over all possible polarizations. We show that the GR and QFT approaches give the same answer.