Classical Limit of Higher-Spin String Amplitudes


Authors: Lucile Cangemi, Paolo Pichini

Preprint number: UUITP-30/22

Abstract: It has been shown that a special set of three-point amplitudes between
two massive spinning states and a graviton reproduces the linearised stress-energy
tensor for a Kerr black hole in the classical limit. In this work we revisit this result
and compare it to the analysis of the amplitudes describing the interaction of leading
Regge states of the open and closed superstring. We find an all-spin result for the
classical limit of two massive spinning states interacting with a photon or graviton.
This result differs from Kerr and instead matches the current four-vector and the
stress-energy tensor generated by a classical string coupled to electromagnetism and
gravity respectively. For the superstring amplitudes, contrary to
the black-hole case, we find that the spin to infinity limit is necessary to generate
the correct classical spin multipoles.