Spinning Guest Fields during Inflation: Leftover Signatures

TL;DR

This paper investigates the potential signatures of extra spinning particles, specifically spin-2, during inflation, focusing on their gravitational wave and non-Gaussianity signals detectable by upcoming CMB experiments.

Contribution

It introduces a comprehensive analysis of spin-2 fields during inflation using non-linear theories, identifying observable signatures within the parameter space.

Findings

Potential detection of local-type non-Gaussianity in gravitational waves

Identification of parameter regions with observable signatures

Ensured stability of the inflationary model throughout cosmic evolution

Abstract

We consider the possibility of extra spinning particles during inflation, focussing on the spin-2 case. Our analysis relies on the well-known fully non-linear formulation of interacting spin-2 theories. We explore the parameter space of the corresponding inflationary Lagrangian and identify regions therein exhibiting signatures within reach of upcoming CMB probes. We provide a thorough study of the early and late-time dynamics ensuring that stability conditions are met throughout the cosmic evolution. We characterise in particular the gravitational wave spectrum and three-point function finding a local-type non-Gaussianity whose amplitude may be within the sensitivity range of both the LiteBIRD and CMB-S4 experiments.