Quantum Stability of a w < - 1 Phase of Cosmic Acceleration

TL;DR

This paper investigates the quantum stability of a super-accelerating phase in cosmic inflation driven by a scalar field, demonstrating that quantum corrections do not lead to instability or tachyonic behavior.

Contribution

It provides a detailed analysis of linearized perturbations in a quantum-corrected framework, confirming the stability of a super-acceleration phase in de Sitter space.

Findings

Quantum effects induce a temporary super-acceleration phase.

The system develops a positive, non-tachyonic mass squared.

The quantum-corrected mode functions confirm stability.

Abstract

We consider a massless, minimally coupled scalar with a quartic self-interaction which is released in Bunch-Davies vacuum in locally de Sitter background of an inflating universe. It was shown, in this system, that quantum effects can induce a temporary phase of super-acceleration causing a violation of the Weak Energy Condition on cosmological scales. In this paper we investigate the system's stability by studying the behavior of linearized perturbations in the quantum-corrected effective field equation at one and two-loop order. We show that the time dependence we infer from the quantum-corrected mode function is in perfect agreement with the system developing a positive mass squared. The maximum induced mass remains perturbatively small and it does not go tachyonic. Thus, the system is stable.