Positronium-like states from supergravity

We study semi-classical rotating open strings ending on a probe Dp-brane close to a stack of extremal, non-extremal Dp-branes and Dp-branes with B  -fields. These states may be interpreted as positronium-like bound states of spinning W-bosons in an SU(N+1)→SU(N)×U(1)SU(N+1)→SU(N)×U(1) theory. In each case, we describe the behaviour of the strings and examine the relation between the energy and the angular momentum of the bound state.