Amplifying the Cosmological Collider with Ghost Spectators

TL;DR

This paper introduces a ghost condensate spectator field in inflationary models, enhancing primordial non-Gaussianity and the bispectrum signal by modifying dispersion relations, thus enriching the cosmological collider framework.

Contribution

It proposes a novel ghost-inspired setup with modified dispersion relations that amplifies collider signals and derives the governing equations for cosmological correlators in this context.

Findings

Enhanced bispectrum signal due to weakened Boltzmann suppression

Horizon-crossing scale remains a free parameter

Distinct differential equations reflecting quadratic dispersion relation

Abstract

Ghost inflation is a well-known framework in which cosmological fluctuations can generate enhanced primordial non-Gaussianity, typically of the equilateral type. In its original form, however, it is in tension with current observational constraints. Here we instead consider a setup in which a standard inflaton drives the background evolution, while excitations of a ghost condensate act as spectator fields that interact with the inflaton. This proposal fits naturally within the cosmological collider program: the exchanged particle has a modified dispersion relation, $\omega \propto k^2$. We show that this ghost-inspired dynamics weakens the usual Boltzmann suppression, similarly to models with a very small effective sound speed, yielding an enhanced bispectrum signal relative to standard cosmological collider scenarios. At the same time, the horizon-crossing scale remains a free parameter of the theory. As a result, the model shares features of both the de Sitter bootstrap and boostless frameworks. Finally, we derive the differential equations governing cosmological correlators in the ghost-collider setup. Their structure reflects the quadratic momentum dependence of the dispersion relation and distinguishes this scenario from conventional relativistic cases.