Model-independent dark energy differentiation with the ISW effect

TL;DR

Cosmological variance severely restricts the class of models distinguishable from one based on cold dark matter and a cosmological constant unless w(z) currently satisfies w(o)(Q)>-0.8, which may place a fundamental limit on the understanding of the origin of the currently observed acceleration.

Abstract

We study the integrated Sachs-Wolfe (ISW) effect using a model-independent parameterization of the dark energy equation of state. Cosmic variance severely restricts the class of models distinguishable from Lambda-CDM. In particular if the present value of the equation of state satisfies w_Q^o <-0.8, the only distinguishable models are those with a rapidly varying equation of state, characterized by a late transition occurring at redshifts z<3. Due to the degeneracy with other cosmological parameters, models with a slowly varying behavior cannot be differentiated from each other or from a cosmological constant using even cosmic variance-limited CMB measurements. This may place a fundamental limit on our understanding of the origin of the presently observed acceleration.

Figures (5)

• Figure 1: Time evolution of the equation of state for two classes of models, with slow (red solid line) and rapid transition (blue dotted line). The dark energy parameters specify the features of $w_Q(a)$
• Figure 2: Power spectrum of the ISW for rapidly varying models (top panels) and slowly varying ones (bottom panels). The solid red line is the ISW effects produced in the cosmological constant case. Detailed explanation in the text.
• Figure 3: Relative difference of $H_1$ (blue solid line), $H_2$ (green dash line) and $H_3$ (red dash-dot line) to the $\Lambda$CDM model, for rapidly varying models ($top$$panels$), and with slow transition ($bottom$$panels$). For these models the present value of the equation of state is $w_Q^o=-1$.
• Figure 4: As in fig.3 for $w_Q^o=-0.88$.
• Figure 5: Relative difference of $l_1$ (blue solid line), $l_2$ (green dashed line) and $l_3$ (red dot-dashed line) to the $\Lambda$CDM model, for rapidly varying models ($top$$panels$), and with slow transition ($bottom$$panels$). For these models the present value of the equation of state is $w_Q^o=-1$.