A New Test for Dark Energy Models

Abstract

(Abridged) Tests that have been proposed to differentiate among dark energy (DE) models are based on observations of galaxies at high redshift (z>0), to be obtained in the future. We suggest here a new test that is valid at z\simeq 0. It is based on existing observational data, numerical simulations, and three well known analytic models that evaluate the bias parameter b, the ratio of galaxy to dark matter (DM) fluctuations. These analytic models are based on the physical processes involved in the formation of stars and in the formation and merging of galaxies. The value of b(z) obtained in each model is a function of the DM growth factor D(z), which, in turn, is a function of the DE. We show that the equations for b in all three analytic models can be reduced to the form of a known constant plus the term E[D(z=0)/D(z)]^α, where α=1 or 2 and E is a free parameter. Using the value of b obtained by the 2dFGRS consortium for the \LambdaCDM model, to normalize E, we find that all three analytic models predict b^2(0)=1\pm 0.1 for all DE models. Numerical simulations that evaluated b^2(0) for the \LambdaCDM and CDM (Λ=0) models also obtained b^2(0)=1\pm 0.1. Since this value of b^2(0) is indicated by numerical simulations as well as by all three popular analytic models, which are normalized by the 2dFGRS consortium result for the \LambdaCDM model, we suggest the condition that b^2(0)=1\pm 0.1 at z=0 as a new test for the viability of dark energy models. Thus, for a given observed galaxy fluctuation spectrum such as that of the 2dFGRS consortium, if the DM fluctuations are greater or less than the galaxy fluctuations by more than 10%, the DE model can be discarded.