Spinning Guest Fields during Inflation: Leftover Signatures
  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.
