  We develop a spinor helicity formalism for five-dimensional scattering
amplitudes of any mass and spin configuration. While five-dimensional spinor
helicity variables have been previously studied in the context of N=2,4
supersymmetric Yang-Mills scattering amplitudes with spin less than two
arXiv:2202.08257, we propose an alternative viewpoint that stems from
d-dimensional spinor helicity variables avoiding the use of the exceptional
low-dimensional isomorphism $SO(4,1) \cong USp(2,2)$ and the decomposition of a
massive momentum into the sum of two massless momenta. By enumerating all
possible independent little group tensors, we systematically build the full
space of five-dimensional three-point tree-level scattering amplitudes for any
configuration of spins and masses. Furthermore, we provide a prescription for
computing the high energy limit of scattering amplitudes written in our spinor
helicity variables. We also expect that our formalism will be applicable to
effective field theories with higher spin, in particular, the scattering of
highly spinning black holes in five dimensions.
