Hidden Negative Energies in Strongly Accelerated Universes

TL;DR

This paper reveals that certain cosmological acceleration theories with near-de Sitter equations of state can secretly violate the null energy condition, leading to infinitely negative energy densities for some observers, despite being free of instabilities.

Contribution

It uncovers hidden violations of the null energy condition in models of accelerated universes with near-de Sitter equations of state.

Findings

Theories with w close to -1 may violate the null energy condition.

Such violations imply observers can perceive infinitely negative energies.

Perturbations remain free of ghosts and gradient instabilities.

Abstract

We point out that theories of cosmological acceleration which have equation of state, w, such that 1+w is small but positive may still secretly violate the null energy condition. This violation implies the existence of observers for whom the background has infinitely negative energy densities, despite the fact that the perturbations are free of ghosts and gradient instabilities.