Comparison of global networks of third-generation gravitational-wave detectors

TL;DR

The paper compares global networks comprising a 40 km Cosmic Explorer in the US with European third-generation detectors in three ET configurations (ET-Δ, ET-2L, and a single L-shaped 1L_EU) and optional LIGO-India, using Fisher-matrix GWFAST analyses. It finds that ET-2L + CE-40km generally yields the best BBH and BNS parameter estimation and localization, with horizons around $z\sim8$–$9$, while 1L_EU + CE-40km serves as a viable interim option, and LIGO-India substantially enhances angular localization when added to 1L_EU. Pre-merger alert capabilities favor configurations with ET-LF, where these networks can issue alerts many hours before merger, whereas 1L_EU configurations lag in early warnings. Sensitivity to stochastic backgrounds improves in 3G networks, though correlated noise in a triangle could severely limit low-frequency performance, underscoring the trade-offs between network complexity and science reach. Overall, the study supports pursuing either the full ET-2L network or, as a backup, a 1L_EU + CE-40km network with LIGO-India, to maximize scientific return across compact binaries and stochastic backgrounds.

Abstract

We study the performances of a world-wide network made by a European third-generation gravitational-wave (GW) detector, together with a 40km Cosmic Explorer detector in the US, considering three scenarios for the European detector: (1) Einstein Telescope (ET) in its 10km triangle configuration; (2) ET in its configuration featuring two 15km L-shaped detectors in different sites, still taken to have all other ET characteristics (underground, and with each detector made of a high-frequency interferometer and a cryogenic low-frequency interferometer); (3) A single L-shaped underground interferometer with the ET sensitivity curve, either with 15km or with 20km arm length. Overall, we find that, if a configuration with two widely separated L-shaped detectors ("2L") should be retained for ET, the network made by a single-L European underground detector together with CE-40km could already provide a very interesting intermediate step toward the construction of a full 2L+CE network, and is in any case superior to a 10km triangle not inserted in an international network. We also study the performance of a network made by a single L-shaped underground interferometer with the ET sensitivity curve together with a single 40km CE and with LIGO-India (taken at A# sensitivity), and we find that it also has very interesting performances.

Figures (8)

• Figure 1: Amplitude spectral densities (ASDs) used in this work. Note that the ASDs are always defined as if we had a single L-shaped detector of the given arm-length; for the triangle, they are then combined as discussed in Branchesi:2023mws.
• Figure 2: Detector horizons for equal mass, non-spinning binaries for the various detector geometries considered. We also add, for comparison, LVKI O5.
• Figure 3: Cumulative distributions of the number of detections per year, for the SNRs and for the error on the parameters, for BBH signals, for the various detector configurations considered.
• Figure 4: Redshift distribution of BBHs detected with ${\rm SNR} \geq 100$ (left column), or relative error on the luminosity distance $\Delta d_L/d_L \leq 0.05$ (central column), or sky location $\Delta\Omega_{90\%} \leq 10~{\rm deg}^2$ (right column) for the various detector configurations considered.
• Figure 5: Cumulative distributions of the number of detections per year, for the SNRs and for the error on the parameters, for BNS signals, for the various detector configurations considered.