Two new diagnostics of dark energy
Abstract
We introduce two new diagnostics of dark energy (DE). The first, Om, is a combination of the Hubble parameter and the cosmological redshift and provides a null test of dark energy being a cosmological constant Λ. Namely, if the value of Om(z) is the same at different redshifts, then DE≡Λ, exactly. The slope of Om(z) can differentiate between different models of dark energy even if the value of the matter density is not accurately known. For DE with an unevolving equation of state, a positive slope of Om(z) is suggestive of phantom (w<1) while a negative slope indicates quintessence (w>1). The second diagnostic—acceleration probe q¯—is the mean value of the deceleration parameter over a small redshift range. It can be used to determine the cosmological redshift at which the universe began to accelerate, again without reference to the current value of the matter density. We apply the Om and q¯ diagnostics to the Union data set of type Ia supernovae combined with recent data from the cosmic microwave background (Wilkinson Microwave Anisotropy Probe 5) and baryon acoustic oscillations.
 Publication:

Physical Review D
 Pub Date:
 November 2008
 DOI:
 10.1103/PhysRevD.78.103502
 arXiv:
 arXiv:0807.3548
 Bibcode:
 2008PhRvD..78j3502S
 Keywords:

 98.80.k;
 95.36.+x;
 Cosmology;
 Dark energy;
 Astrophysics;
 General Relativity and Quantum Cosmology;
 High Energy Physics  Theory
 EPrint:
 14 pages, 9 figures. Some new results and an additional reference. Main conclusions unchanged. Matches published version