On the Classical and Quantum Stability of a Cosmic Ghost

TL;DR

This paper investigates the stability of a ghost-dilaton system in cosmology, demonstrating classical stability through phase space analysis and exploring conditions to prevent quantum instabilities, relevant for phenomenological models.

Contribution

It provides a detailed analysis of the classical and quantum stability of ghost fields coupled to gauge sectors, introducing new stability conditions and potential configurations to avoid instabilities.

Findings

Classical stability achieved via limit cycles in phase space.

Identified parameter ranges for stable gauge-invariant perturbations.

Discussed mechanisms like ghost condensates to prevent quantum instabilities.

Abstract

Ghost fields have reemerged in a handful of phenomenologically motivated cosmological and particle physics scenarios, and most recently in a cyclic mechanism to address the fine-tuning of gauge couplings in the standard model. We study the classical and quantum stability of a ghost-dilaton system coupled to a gauge sector and find that this system is classically stable due to the existence of limit cycles in phase space. We also analyze the coupled gauge invariant classical perturbations and find a range of phenomenologically viable parameters where the system is stable. We also discuss ways to avoid both quantum and vacuum instabilities by either having a ghost condensate or Classicon configurations.