Understanding the origin of CMB constraints on dark energy

Abstract

We study the observational constraints of cosmic microwave background (CMB) temperature and polarization anisotropies on models of dark energy, with special focus on models with variation in properties of dark energy with time. We demonstrate that the key constraint from CMB observations arises from the location of acoustic peaks. An additional constraint arises from the limits on ΩNR from the relative amplitudes of acoustic peaks. Further, we show that the distance to the last scattering surface is not how the CMB observations constrain the combination of parameters for models of dark energy. We also use constraints from supernova observations and show that unlike the gold and silver samples, the Supernova Legacy Survey (SNLS) sample prefers a region of parameter space that has a significant overlap with the region preferred by the CMB observations. This is a verification of a conjecture made by us in an earlier work. We discuss combined constraints from Wilkinson Microwave Anisotropy Probe 5‐yr and SNLS observations. We find that models with w≃− 1 are preferred for models with a constant equation‐of‐state parameters. In case of models with a time‐varying dark energy, we show that constraints on evolution of dark energy density are almost independent of the type of variation assumed for the equation‐of‐state parameter. This makes it easy to get approximate constraints from CMB observations on arbitrary models of dark energy. Constraints on models with a time‐varying dark energy are predominantly due to CMB observations, with supernova constraints playing only a marginal role.

Observational constraints on interacting dark matter model without dark energy

“…A new type of matter with negative pressure, which is popularly known as dark energy, has been proposed to explain the present phase of acceleration. The most simple dark energy candidate, the cosmological constant (ΛCDM model), though known to be consistent with various observations such as SNe Ia, the galaxy cluster gas mass fraction data (Wilson et al 2006;Davis et al 2007;Allen et al 2008), and the CMB temperature and polarization anisotropies (Jassal et al 2010), is always affected by the coincidence problem. Until now, many other dark energy models have been brought forward to explain this comic acceleration such as the scalar fields with a dynamical equation of state (e.g., quintessence, Peebles & Ratra 1988a,b;Caldwell et al 1998;phantom, Caldwell 2002;k-essence, Armendariz-Picon et al 2001;quintom, Feng et al 2005;Guo et al 2005;Liang et al 2009), the Chaplygin gas (Kamenshchik et al 2001;Bento et al 2002), holographic dark energy (Cohen 1999;Li 2004), and so on.…”

Can holographic dark energy increase the mass of the wormhole?

“…In the next phase of the study we have adopted three dark energy parameterization schemes w CP L (z) = w 0 + w 1 z 1+z , w JBP (z) = w 0 + w 1 z (1+z) 2 , w log (z) = w 0 + w 1 ln(1 + z) proposed in [58][59][60]. In this phase we have not assumed any form of the scale factor and solved the conservation equations to get the dark energy densities under the three parameterization schemes.…”

“…Jassal et al [59] used a parameterization of the form that is obtainable by putting m = 2 in Family II. Since a = (1 + z) −1 , the conservation equation takes the form…”

Reconstruction of the equation of state for the cyclic universes in homogeneous and isotropic cosmology

“…ForḢ = 0, eff = −1, which corresponds to the cosmological constant. It is significant to remark that recent various observational data [139][140][141][142][143][144] implies that the crossing of the phantom divide line of DE = −1 occurred in the near past. Here, DE is the EoS for dark energy and at the dark energy dominated stage, it can be regarded that ≈ DE ≈ eff .…”