Constraints on a Massive Double-Copy and Applications to Massive Gravity

Understand

We propose and study a BCJ double-copy of massive particles, showing that it is equivalent to a KLT formula with a kernel given by the inverse of a matrix of massive bi-adjoint scalar amplitudes.

• For models with a uniform non-zero mass spectrum we demonstrate that the resulting double-copy factors on physical poles and that up to at least 5-particle scattering, color-kinematics satisfying numerators always exist.
• For the scattering of 5 or more particles, the procedure generically introduces spurious singularities that must be cancelled by imposing additional constraints.
• When massive particles are present, color-kinematics duality is not enough to guarantee a physical double-copy.