Crossing the Phantom Divide with Parameterized Post-Friedmann Dark Energy

TL;DR

This paper introduces a parameterized post-Friedmann framework that accurately models crossing the dark energy equation of state divide, enabling stable and consistent cosmological predictions for complex scalar field models.

Contribution

It provides a simple, accurate, and publicly available description for scalar field crossing dark energy models within the post-Friedmann formalism.

Findings

Accurately models scalar field crossing dark energy models

Conserves energy and momentum in the description

Applicable to a wide range of smooth dark energy models

Abstract

Dark energy models with a single scalar field cannot cross the equation of state divide set by a cosmological constant. More general models that allow crossing require additional degrees of freedom to ensure gravitational stability. We show that a parameterized post-Friedmann description of cosmic acceleration provides a simple but accurate description of multiple scalar field crossing models. Moreover the prescription provides a well controlled approximation for a wide range of "smooth" dark energy models. It conserves energy and momentum and is exact in the metric evolution on scales well above and below the transition scale to relative smoothness. Standard linear perturbation tools have been altered to include this description and made publicly available for studies of the dark energy involving cosmological structure out to the horizon scale.