Cosmological Gravitational Wave Collider Physics

Abstract

Primordial tensor non-Gaussianity can probe massive particles present during inflation. We investigate this possibility in an effective field theory where the massless graviton mixes with the helicity-two mode of an additional massive spin-two field $σ_{ij}$ with cubic self-interactions. For constant sound speed, we compute the leading tensor power-spectrum correction and the tree-level bispectrum, finding novel analytical expressions for these quantities. In the $m_σ>3H/2$ regime, we find a nonanalytic squeezed contribution that exhibits logarithmic oscillations with characteristic dependence $(k_L/k_S)^{3/2\pm iμ}$, where $μ=\sqrt{m_σ^2/H^2-9/4}$. The oscillation frequency is set by the mass $m_σ$, while the polarisation contractions determine the relative amplitudes of the different graviton helicity configurations. The same mixing generates corrections to the power spectrum and the bispectrum. We derive the associated quadrupolar modulation of short-scale tensor power spectrum and relate its amplitude to the model parameters. Finally, we explore how a slowly varying sound speed modifies the squeezed signal.~These results connect the two-point, three-point, and quadrupolar tensor signatures of massive spin-two fields in the cosmological gravitational wave collider.