On the Inflationary Perturbations of Massive Higher-Spin Fields

TL;DR

This work demonstrates that massive higher-spin fields, ordinarily constrained from leaving the Higuchi bound during inflation, can be engineered to possess long-lived super-Hubble perturbations by coupling them to time-dependent inflaton functions. Through a bottom-up analysis of spin-1, spin-2, and general spin-$s$ fields, the authors derive the required inflaton couplings, mass structures, and gauge-like symmetries that stabilize certain helicities on super-Hubble scales. They show that, for specific parameter choices, enhanced symmetries emerge, effectively reducing the propagating degrees of freedom to helicities $\pm s$, or even to massless-like sectors, depending on the case. The paper also outlines observable consequences, including anisotropic signatures in the scalar four-point function and corrections to the curvature power spectrum, offering potentially detectable imprints of a higher-spin sector during inflation.

Abstract

Cosmological perturbations of massive higher-spin fields are generated during inflation, but they decay on scales larger than the Hubble radius as a consequence of the Higuchi bound. By introducing suitable couplings to the inflaton field, we show that one can obtain statistical correlators of massive higher-spin fields which remain constant or decay very slowly outside the Hubble radius. This opens up the possibility of new observational signatures from inflation.