String Theory and the Velo-Zwanziger problem

We examine the behavior of the leading Regge trajectory of the open bosonic string in a uniform electromagnetic background and present a consistent set of Fierz-Pauli conditions for these symmetric tensors that generalizes the Argyres-Nappi spin-2 result. These equations indicate that String Theory does bypass the Velo-Zwanziger problem, i.e. the loss of causality experienced by a massive high-spin field minimally coupled to electromagnetism. Moreover, we provide some evidence that only the first Regge trajectory can be described in isolation and show that the open-string spectrum is free of ghosts in weak constant backgrounds. Finally, we comment on the roles of the critical dimension and of the gyromagnetic ratio.