Massive higher spin states in string theory and gravitational quadrupoles

In this paper we study three point functions of the type II superstring involving one graviton and two massive states, focusing in particular on the spin-7/2 fermions at the first mass level. Defining a gravitational quadrupole "h factor," we find that the nonminimal interactions of string states in general are parametrized by h ≠ 1, in contrast with the preferred field theory value of h = 1 (for tree-level unitarity). This difference arises from the fact that consistent gravitational interactions of strings are related to the presence of a complete tower of massive states, not present in the ordinary field theory case.