A litmus test for Lambda

TL;DR

This paper introduces consistency tests for the cosmological constant, enabling direct observational validation or refutation of Lambda regardless of matter and curvature densities, using future supernova data.

Contribution

It proposes novel consistency tests for Lambda that do not depend on matter or curvature densities, improving robustness of dark energy model assessments.

Findings

The flat case test can detect 20% deviations from w=-1 at 4-sigma with SNAP data.

The tests can rule out many non-Lambda models without knowing Omega_m.

Effective with large supernova datasets like LSST.

Abstract

The critical issue in cosmology today lies in determining if the cosmological constant is the underlying ingredient of dark energy. Our profound lack of understanding of the physics of dark energy places severe constrains on our ability to say anything about its possible dynamical nature. Quoted errors on the equation of state, w(z), are so heavily dependent on necessarily over-simplified parameterisations they are at risk of being rendered meaningless. Moreover, the existence of degeneracies between the reconstructed w(z) and the matter and curvature densities weakens any conclusions still further. We propose consistency tests for the cosmological constant which provide a direct observational signal if Lambda is wrong, regardless of the densities of matter and curvature. As an example of its utility, our flat case test can warn of a small transition from w(z)=-1 of 20% from SNAP quality data at 4-sigma, even when direct reconstruction techniques see virtually no evidence for deviation from Lambda. It is shown to successfully rule out a wide range of non-Lambda dark energy models with no reliance on knowledge of Omega_m using SNAP-quality data and a large range for using 10^5 supernovae as forecasted for LSST.