Cosmology with space-based gravitational-wave detectors --- dark energy and primordial gravitational waves ---

TL;DR

Future space-based gravitational-wave detectors like DECIGO and BBO can measure high-redshift cosmological expansion and probe dark energy without electromagnetic redshift data, while also aiming to detect primordial gravitational waves by subtracting neutron-star binary signals.

Contribution

This paper analyzes the potential of space-based GW detectors to constrain dark energy and detect primordial GWs, considering detector sensitivity and binary foreground subtraction.

Findings

High-precision luminosity distance measurements enable dark energy constraints.

Detection of primordial GWs depends on effective subtraction of neutron-star binary foreground.

Detector sensitivity requirements are identified for successful cosmological studies.

Abstract

Proposed space-based gravitational-wave (GW) detectors such as DECIGO and BBO will detect ~10^6 neutron-star (NS) binaries and determine the luminosity distances to the binaries with high precision. Combining the luminosity distances with cosmologically-induced phase corrections on the GWs, cosmological expansion out to high redshift can be measured without the redshift determinations of host galaxies by electromagnetic observation and be a unique probe for dark energy. On the other hand, such a NS-binary foreground should be subtracted to detect primordial GWs produced during inflation. Thus, the constraining power on dark energy and the detectability of the primordial gravitational waves strongly depend on the detector sensitivity and are in close relation with one another. In this paper, we investigate the constraints on the equation of state of dark energy with future space-based GW detectors with/without identifying the redshifts of host galaxies. We also study the sensitivity to the primordial GWs, properly dealing with the residual of the NS binary foreground. Based on the results, we discuss the detector sensitivity required to achieve the forementioned targeted study of cosmology.