Causality of higher-spin interactions on the (A)dS lightcone, with application to the static patch

TL;DR

This paper investigates higher-spin gravity interactions in (A)dS space using lightcone formalism, extending the framework to de Sitter space and exploring causal properties and static patch scattering amplitudes.

Contribution

It introduces a generalized lightcone formalism for higher-spin interactions in (A)dS, enabling the study of causal properties and static patch scattering amplitudes in de Sitter space.

Findings

Extended lightcone formalism to broader frames including de Sitter space

Verified causal properties of massless higher-spin interactions

Developed a scheme to compute static patch scattering amplitudes

Abstract

We study Higher-Spin Gravity in 4-dimensional (Anti-)de Sitter space, at leading order in the interactions (cubic vertices), in the AdS lightcone formalism developed by Metsaev. Using the vertices' chiral structure, we extend the formalism into a broader class of lightcone frames, which allows for lightcones of bulk points. This enables us to write the lightcone theory in de Sitter space, where only these more general frames are available. It also allows us to formulate and verify (for the first time!) some causal properties of massless higher-spin interactions, involving lightcone foliations that share a lightray. These causal properties serve to both motivate and enable the computation of "static-patch scattering amplitudes" - the evolution of fields between the two horizons of the maximal observable region in de Sitter space. We present a computation scheme for such "amplitudes" in coordinate space, and in momentum space with spinor-helicity variables.