One of the greatest challenges in cosmology today is to determine the nature of dark energy , the source of the observed present acceleration of the universe .
High precision experiments are being developed to reduce the uncertainties in the observations .
Recently , we showed that the agreement to an accuracy of 10 \% of measurements of the present density fluctuations ( \delta \rho / \rho ) ^ { 2 } , derived from galaxy distribution ( GD ) data and cosmic microwave background ( CMB ) anisotropies in the \Lambda CDM model , puts very strong limits on the possible decay of the vacuum energy into cold dark matter .
Using this agreement , combined with the evidence that the matter density \Omega _ { M } ^ { 0 } = 0.28 \pm 0.02 and that the universe is approximately flat , we show that the vacuum metamorphosis model ( VMM ) and the popular brane-world model ( BWM ) , both used to explain dark energy , can be discarded .
When we relax the \Omega _ { M } ^ { 0 } requirement , we find that an agreement within 10 \% can be obtained only with \Omega _ { M } ^ { 0 } \simeq 0.36 for the VMM and \Omega _ { M } ^ { 0 } \simeq 0.73 for the BWM , both of which are not consistent with observations .
The agreement of the CMB and GD data and previous constraints from SNIa data exclude , or put strong limits on , other dark energy models , which have been suggested , that can be described by the parametrized equation of state ( EOS ) w = p / \rho = w _ { 0 } + w _ { a } ( 1 - a ) , where w _ { 0 } and w _ { a } are constants , a is the cosmological scale factor and p ( \rho ) is the pressure ( energy density ) of the dark energy .
We find that the supergravity ( SUGRA ) model with w _ { 0 } = -0.82 and w _ { a } = 0.58 can be discarded .
In general , we find best values -1.86 < w _ { 0 } < -1.72 with 1.53 < w _ { a } < 2.0 .
For redshifts z \sim 0.5 - 1 , where the supernova data is sensitive , w \sim - 1 for this parametrized EOS .