Non-Relativistic Cosmological Collider Signals

TL;DR

This paper explores a non-relativistic inflationary model with a tilted-ghost spectator field, revealing unique non-Gaussian signatures and a new dynamical mechanism distinct from standard boostless collider scenarios.

Contribution

It introduces a novel non-relativistic realization of the boostless cosmological collider with a tilted-ghost field, highlighting a different origin for non-Gaussian signals.

Findings

Non-Gaussian signals are generated by spectator mode propagation, not boost-breaking interactions.

Tilted-ghost modes induce a characteristic tilt in mode functions, affecting correlators.

The model features an effective chemical-potential-like parameter influencing late-time oscillations.

Abstract

We investigate a non-relativistic realization of the boostless cosmological collider in a scenario where inflationary interactions are mediated by a massive tilted-ghost spectator field. Unlike standard boostless collider constructions, in which the characteristic non-Gaussian signatures are mainly generated by boost-breaking interaction vertices, the dominant effect in the present framework arises directly from the propagation of the spectator modes. Non-relativistic corrections deform the bulk mode functions, inducing a tilt that modifies the in-in correlators and generates a distinctive collider signal. The resulting squeezed-limit non-Gaussianity reproduces the qualitative structure of boostless cosmological-collider signals while originating from a fundamentally different dynamical mechanism. A central feature of the construction is the emergence of an effective chemical-potential-like parameter that controls the relative weight of the two late-time oscillatory branches. However, the tilted-ghost mode exhibits distinctive dynamical features and does not correspond to a conventional chemical-potential deformation. Depending on the sign of the tilt, the corresponding non-Gaussian signal can be either enhanced or suppressed. We show that the tilted-ghost scenario provides a simple effective framework in which boostless-collider phenomenology and chemical-potential-like branch asymmetries arise naturally from non-relativistic propagation effects.