Constraining dark energy with SNe Ia and large-scale structure

TL;DR

This study addresses the nature of dark energy by combining type Ia supernovae (SNe Ia) distance measurements with large-scale structure (LSS) and other cosmological data in a flat, cold dark matter framework. It uses an effective dark-energy equation of state $w_{\rm eff}$ within dynamical scalar-field models, constraining $(\Omega_M, w_{\rm eff})$ via marginalized likelihoods that incorporate COBE normalization, power-spectrum shape, baryon density, and cluster abundance. The joint SN Ia, LSS, and CMB analysis finds $\Omega_X \in (0.6,0.7)$ and $w_{\rm eff} < -0.6$ (95% CL), with $w_{\rm eff}$ near $-1$, strongly supporting a cosmological constant over tracker or topological-defect scenarios. The results are robust to modest changes in flatness and gravity-wave contributions to the CMB, reinforcing the Lambda-CDM paradigm as the simplest explanation for cosmic acceleration.

Abstract

Measurements of the distances to SNe Ia have produced strong evidence that the expansion of the Universe is accelerating, implying the existence of a nearly uniform component of dark energy with negative pressure. We show that constraints to this mysterious component based upon large-scale structure nicely complement the SN Ia data, and that together they require Omega_X = (0.6,0.7) and w_X < -0.6 (95% cl), for the favored flat Universe. Other cosmological data support this conclusion. The simplest explanation, a cosmological constant, is consistent with this, while some of the other possibilities are not.

Figures (2)

• Figure 1: Contours of likelihood, from $0.5\sigma$ to $2\sigma$, in the $\Omega_M$--$w_{\rm eff}$ plane. Left: The thin solid lines are the constraints from LSS and the CMB. The heavy lines are the SN Ia constraints (using the Fit C supernovae of Ref. scp) for constant $w$ models (solid curves) and for a scalar-field model with an exponential potential (broken curves; quadratic and quartic potentials have very similar SN Ia constraints). Note that the SN Ia contours for dynamical scalar-field models and constant $w$ models are slightly offset (see text). Right: The likelihood contours from all of our cosmological constraints for constant $w$ models (solid) and dynamical scalar-field models (broken).
• Figure 2: Upper panel: The relationship between $w_{\rm eff}$ and $\Omega_M$ for a selection of tracker potentials. Lower panels: the CMB and LSS likelihoods from Fig. \ref{['fig:composite']} as a function of $\Omega_M$ (dotted) and the SN Ia likelihood (solid -- normalized to unity at the peak). As can be seen clearly, tracker models have difficulty simultaneously accommodating the SN Ia and LSS constraints.