Possible Signatures of Inflationary Particle Content: Spin-2 Fields

TL;DR

This paper investigates how a massive spin-2 field during inflation could leave detectable signatures on cosmological observables, focusing on consistency relation violations and ensuring ghost-free interactions.

Contribution

It introduces a model with a massive spin-2 field interacting via dRGT terms during inflation, analyzing its observable imprints and the role of the Higuchi bound.

Findings

Massive spin-2 fields can produce observable signatures in inflationary data.

The Higuchi bound constrains the strength of signals from spin-2 particles.

Ghost-free interactions are achieved through dRGT coupling.

Abstract

We study the imprints of a massive spin-2 field on inflationary observables, and in particular on the breaking of consistency relations. In this setup, the minimal inflationary field content interacts with the massive spin-2 field through dRGT interactions, thus guaranteeing the absence of Boulware-Deser ghostly degrees of freedom. The unitarity requirement on spinning particles, known as Higuchi bound, plays a crucial role for the size of the observable signal.