Five-dimensional Geometry from Spinning Amplitudes

Abstract

Massive spinor-helicity variables in four dimensions are a useful tool for studying amplitudes between higher-spin fields and gravitons. Among them a special, simple set of amplitudes reproduces the linearized stress-energy tensor of a Kerr black hole in the classical limit. In this work we initiate the study of the classical limit of three-point spinor-helicity amplitudes in five dimensions. We introduce the map between the spinor invariants and the expectation values of spin operators and match the amplitude building blocks with those of the multipole expansion. Interestingly, in order to take the classical limit of a general amplitude, we need to augment the multipole structures with the Hodge dual of the classical spin tensor. We study the classical limit of alternative spinning states not described by fully-symmetric products of polarisations and conclude that they can describe the same spacetimes. Finally, by relaxing the orthogonality condition of the spin tensor we are able to model spacetimes with a single rotational isometry and match these to the classical limit of amplitudes allowing for an internal spin shift. Along the way we also identify the class of amplitudes describing the Myers-Perry black hole and comment on its generalization to arbitrary dimensions.