CONSTRAINING PERTURBATIVE EARLY DARK ENERGY WITH CURRENT OBSERVATIONS

In this work, we study a class of early dark energy (EDE) models, in which, unlike in standard dark energy models, a substantial amount of dark energy exists in the matter-dominated era. We self-consistently include dark energy perturbations, and constrain these models using current observations. We consider EDE models in which the dark energy equation of state is at least w(m) greater than or similar to -0.1 at early times, which could lead to an EDE density of up to Omega(DE)(z(CMB)) = 0.03 Omega(m)(z(CMB)). Our analysis shows that marginalizing over the non-DE parameters such as Omega(m), H-0, and n(s), current CMB observations alone can constrain the scale factor of transition from EDE to late-time dark energy to a(t) greater than or similar to 0.44 and width of transition to Delta(t) less than or similar to 0.37. The equation of state at present is somewhat weakly constrained to w(0) less than or similar to -0.6, if we allow H-0 < 60 km s(-1) Mpc(-1). Taken together with other observations, such as SNe, Hubble Space Telescope, and Sloan Digital Sky Survey luminous red galaxies, w(0) is constrained much more tightly to w(0) less than or similar to -0.9, while redshift of transition and width of transition are also tightly constrained to a(t) less than or similar to 0.19 and Delta(t) less than or similar to 0.21. The evolution of the equation of state for EDE models is thus tightly constrained to Lambda CDM-like behavior at low redshifts. Incorrectly assuming dark energy perturbations to be negligible leads to different constraints on the equation of state parameters-w(0) less than or similar to -0.8, a(t) less than or similar to 0.33, and Delta(t) less than or similar to 0.31, thus highlighting the necessity of self-consistently including dark energy perturbations in the analysis. If we allow the spatial curvature to be a free parameter, then the constraints are relaxed to w(0) less than or similar to -0.77, a(t) less than or similar to 0.35, and Delta(t) less than or similar to 0.35 with -0.014 < Omega(kappa) < 0.031 for CMB + other observations. For perturbed EDE models, the 2 sigma lower limit on sigma(8) (sigma(8) >= 0.59) is much lower than that in Lambda CDM (sigma(8) >= 0.72), thus raising the interesting possibility of discriminating EDE from Lambda CDM using future observations such as halo mass functions or the Sunyaev-Zeldovich power spectrum.