Misc,
Constraining Perturbative Early Dark Energy with Current Observations
(2010)cite arxiv:1003.1259 Comment: 12 pages, 5 figures.
Abstract
In this work, we study a class of early dark energy (EDE) models, in which,
unlike in standard DE models, a substantial amount of DE exists in the
matter-dominated era, self-consistently including DE perturbations. Our
analysis shows that, marginalizing over the non DE parameters such as $Omega_m,
H_0, n_s$, current CMB observations alone can constrain the scale factor of
transition from early DE to late time DE to $a_t 0.44$ and width of
transition to $Delta_t 0.37$. The equation of state at present is somewhat
weakly constrained to $w_0 -0.6$, if we allow $H_0 < 60$ km/s/Mpc. Taken
together with other observations, such as supernovae, HST, and SDSS LRGs, the
constraints are tighter-- $w_0 -0.9, a_t 0.19, \Delta_t 0.21$.
The evolution of the equation of state for EDE models is thus close to
$Łambda$CDM at low redshifts. Incorrectly assuming DE perturbations to be
negligible leads to different constraints on the equation of state parameters,
thus highlighting the necessity of self-consistently including DE perturbations
in the analysis. If we allow the spatial curvature to be a free parameter, then
the constraints are relaxed to $w_0 -0.77, a_t 0.35, \Delta_t łeq
0.35$ with $-0.014 < Ømega_\kappa < 0.031$ for CMB+other observations. For
perturbed EDE models, the $2\sigma$ lower limit on $\sigma_8$ ($\sigma_8 \geq
0.59$) is much lower than that in $Łambda$CDM ($\sigma_8 0.72$), thus
raising the interesting possibility of discriminating EDE from $Łambda$CDM
using future observations such as halo mass functions or the Sunyaev-Zeldovich
power spectrum.
