Determination of Dark Energy by the Einstein Telescope: Comparing with CMB, BAO and SNIa Observations

TL;DR

The paper assesses the Einstein Telescope's potential to measure dark energy parameters using gravitational wave standard sirens, comparing its capabilities with CMB, BAO, and supernova observations, and emphasizing its role as an independent cosmological probe.

Contribution

It provides a detailed analysis of ET's ability to constrain dark energy parameters by incorporating Planck CMB priors, improving upon previous estimates.

Findings

ET can measure w0 with an accuracy of 0.099

ET can measure wa with an accuracy of 0.302

ET's constraints are comparable to JDEM and SNAP projections

Abstract

A design study is currently in progress for a third generation gravitational-wave (GW) detector called Einstein Telescope (ET). An important kind of source for ET will be the inspiral and merger of binary neutron stars (BNS) up to $z \sim 2$. If BNS mergers are the progenitors of short-hard $\gamma$-ray bursts, then some fraction of them will be seen both electromagnetically and through GW, so that the luminosity distance and the redshift of the source can be determined separately. An important property of these `standard sirens' is that they are \emph{self-calibrating}: the luminosity distance can be inferred directly from the GW signal, with no need for a cosmic distance ladder. Thus, standard sirens will provide a powerful independent check of the $\Lambda$CDM model. In previous work, estimates were made of how well ET would be able to measure a subset of the cosmological parameters (such as the dark energy parameter $w_0$) it will have access to, assuming that the others had been determined to great accuracy by alternative means. Here we perform a more careful analysis by explicitly using the potential Planck CMB data as prior information for these other parameters. We find that ET will be able to constrain $w_0$ and $w_a$ with accuracies $\Delta w_0 = 0.099$ and $\Delta w_a = 0.302$, respectively. These results are compared with projected accuracies for the JDEM Baryon Acoustic Oscillations project and the SNAP Type Ia supernovae observations.