A stringy massive double copy

TL;DR

This paper constructs a massive double copy framework within string theory, deriving massive spin-2 states from open string vectors and demonstrating their double copy structure through amplitude calculations.

Contribution

It introduces a novel massive double copy construction in string theory using open string vectors and reproduces bimetric theory Lagrangian for massive spin-2 states.

Findings

Derived massive double copy structure for spin-2 states

Computed three-point amplitudes confirming double copy

Reproduced bimetric theory Lagrangian from string states

Abstract

We derive a massive double copy construction within string theory. To this end, we use massive vectors of the open string spectrum that appear in compactifications to four dimensions and construct massive spin-2 tensors as closed string states, thereby mimicking the structure of the massless graviton. We then compute three-point amplitudes for the scattering of massless and massive spin-2 closed string states and reveal the double copy structure of the latter. With these results being finite in the string scale, we are further able to reproduce the cubic Lagrangian of ghost-free bimetric theory around flat spacetime for bulk massive spin-2 states originating in products of vectors of extended brane supersymmetry.