Light-Front Higher-Spin Theories in Flat Space

TL;DR

The paper investigates interactions of massless higher-spin fields in flat space using the light-front formalism, showing that traditional no-go theorems can be circumvented and revealing a richer spectrum of vertices than in covariant approaches.It identifies a two-derivative gravitational coupling for higher spins and demonstrates that gravity couples universally across all spins, consistent with an HS extension of the equivalence principle.A complete chiral higher-spin theory in four-dimensional Minkowski space is constructed, with a simple Metsaev-type cubic solution that yields a vanishing tree-level four-point amplitude in the holomorphic sector, though it is non-unitary.To realize a unitary flat-space HS theory, the authors reconstruct a perturbatively local quartic scalar vertex within the full holomorphic/antiholomorphic framework, indicating a path toward a consistent HS model in flat space and highlighting connections to AdS via HS algebras.

Abstract

We revisit the problem of interactions of higher-spin fields in flat space. We argue that all no-go theorems can be avoided by the light-cone approach, which results in more interaction vertices as compared to the usual covariant approaches. It is stressed that there exist two-derivative gravitational couplings of higher-spin fields. We show that some reincarnation of the equivalence principle still holds for higher-spin fields - the strength of gravitational interaction does not depend on spin. Moreover, it follows from the results by Metsaev that there exists a complete chiral higher-spin theory in four dimensions. We give a simple derivation of this theory and show that the four-point scattering amplitude vanishes. Also, we reconstruct the quartic vertex of the scalar field in the unitary higher-spin theory, which turns out to be perturbatively local.