String Lessons for Higher-Spin Interactions

TL;DR

This paper simplifies the understanding of higher-spin interactions in string theory by deriving explicit three- and four-point amplitudes for symmetric tensors, revealing their relation to local couplings and gauge symmetries.

Contribution

It provides a simplified formulation of string amplitudes for higher-spin states and connects them to local couplings, extending previous field theory results and exploring gauge symmetry recovery.

Findings

Derived explicit three- and four-point amplitudes for higher-spin states.

Connected string amplitudes to local couplings and currents.

Discussed gauge symmetry recovery in the low-tension limit.

Abstract

String Theory includes a plethora of higher-spin excitations, which clearly lie behind its most spectacular properties, but whose detailed behavior is largely unknown. Conversely, string interactions contain much useful information on higher-spin couplings, which can be very valuable in current attempts to characterize their systematics. We present a simplified form for the three-point (and four-point) amplitudes of the symmetric tensors belonging to the first Regge trajectory of the open bosonic string and relate them to local couplings and currents. These include the cases first discussed, from a field theory perspective, by Berends, Burgers and van Dam, and generalize their results in a suggestive fashion along lines recently explored by Boulanger, Metsaev and others. We also comment on the recovery of gauge symmetry in the low-tension limit, on the current-exchange amplitudes that can be built from these couplings and on the extension to mixed-symmetry states.