Hidden Negative Energies in Strongly Accelerated Universes

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.

5 pages, 1 figure. v2 reflects version accepted for publication in PRD. Changes: additional discussion of gauge-dependence in perturbed cosmologies