Dodging the dark matter degeneracy while determining the dynamics of dark energy

TL;DR

This paper introduces a robust method to determine dark energy evolution by using a function independent of matter density degeneracy, improving over traditional parameterisations.

Contribution

It presents a simple, matter-density-independent function of dark energy parameters that can be accurately measured with Gaussian Processes from supernova data.

Findings

The function is independent of matter density degeneracy at all redshifts.

Gaussian Processes can accurately determine this function at low redshift.

Parametrised models introduce bias in dark energy evolution constraints.

Abstract

One of the key issues in cosmology is to establish the nature of dark energy, and to determine whether the equation of state evolves with time. When estimating this from distance measurements there is a degeneracy with the matter density. We show that there exists a simple function of the dark energy equation of state and its first derivative which is independent of this degeneracy at all redshifts, and so is a much more robust determinant of the evolution of dark energy than just its derivative. We show that this function can be well determined at low redshift from supernovae using Gaussian Processes, and that this method is far superior to a variety of parameterisations which are also subject to priors on the matter density. This shows that parametrised models give very biased constraints on the evolution of dark energy.