One of the greatest challenges in cosmology today is to determine the nature of dark energy ( DE ) , the source of the observed present acceleration of the Universe .
Besides the vacuum energy , various DE models have been suggested .
The tests that have been proposed to differentiate among these 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 ) ] ^ { \alpha } , where \alpha = 1 or 2 and E is a free parameter .
Using the value of b obtained by the 2dFGRS consortium for the \Lambda CDM model , to normalize E , we find that all three analytic models predict b ^ { 2 } ( 0 ) = 1 \pm 0.1 for all DE models .
Since we use the result that b ^ { 2 } ( 0 ) \simeq 1 from the 2dFGRS consortium for the \Lambda CDM model , the L _ { \ast } galaxy used in our text is the same as that obtained by the consortium for a broad range of galaxy types , using the Schechter function fit to the overall luminosity function of their \sim 220 , 000 galaxies .
Numerical simulations that evaluated b ^ { 2 } ( 0 ) for the \Lambda CDM and CDM ( \Lambda = 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 \Lambda CDM model , we suggest the condition that b ^ { 2 } ( 0 ) = 1 \pm 0.1 at z = 0 as a new test for the viability of DE 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 .
As examples of this test , we show that three popular DE models do not satisfy this test : the vacuum metamorphosis model deviates from b ^ { 2 } ( 0 ) = 1.0 at z = 0 by 20 \% , the brane-world model by 26 \% and the supergravity ( SUGRA ) model by 38 \% .