Exploring the Sensitivity of Next Generation Gravitational Wave Detectors

TL;DR

This paper addresses how next-generation ground-based gravitational-wave detectors can reach cosmological distances with high signal-to-noise, enabling transformative science. It defines target sensitivity for a 40 km detector (Cosmic Explorer) and presents simple scaling relations for dominant noise sources—quantum noise, coating thermal noise, Newtonian noise, suspended/seismic noise, and residual gas noise. It discusses feasible R&D directions (squeezing, cryogenics, larger optics, advanced suspensions, NN cancellation) to attain these targets and compares 40 km performance with the Einstein Telescope baseline. Key science outcomes highlighted include high-SNR CBC detections at high redshift, EOS constraints, tests of GR, and potential observations of extragalactic core-collapse supernovae.

Abstract

The second-generation of gravitational-wave detectors are just starting operation, and have already yielding their first detections. Research is now concentrated on how to maximize the scientific potential of gravitational-wave astronomy. To support this effort, we present here design targets for a new generation of detectors, which will be capable of observing compact binary sources with high signal-to-noise ratio throughout the Universe.

Figures (4)

• Figure 1: Target sensitivity for a next generation gravitational-wave detector, known as "Cosmic Explorer" for its ability to receive signals from cosmological distances. The solid curves are for a $40\,\rm km$ long detector, while the dashed grey curves show the sensitivity of shorter, but technologically similar detectors; lengths are 4, 10 and $20\,\rm km$. The Advanced LIGO and Einstein Telescope design sensitivities are also shown for reference.
• Figure 2: Similar to figure \ref{['fig:target']} but with a more reflective signal extraction mirror which gives a wider sensitive band, but is less sensitive in-band. The tradeoff between in-band sensitivity and bandwidth will need to be optimized to maximize specific science objectives (e.g., testing general relativity with black hole binaries, measuring neutron star equation of state, detection of GW from supernovae, etc.). The dashed grey curves show the sensitivity of shorter, but technologically similar detectors; lengths are 4, 10 and $20\,\rm km$.
• Figure 3: Similar to figure \ref{['fig:wideband']} but with coating and suspension thermal noise models which assume minimal progress. The wide-band signal extraction choice is made to minimize the impact of CTN. The proximity of the dashed grey $4\,\rm km$ curve to the Advanced LIGO reference curve reflects the fact that coating technology, which is nearly limiting in Advanced LIGO, becomes dominant over a range of frequencies given the reduction of quantum noise assumed for the future.
• Figure 4: The maximum signal-to-noise ratio (SNR) for which GW detectors with the sensitivities shown in figures \ref{['fig:target']}, \ref{['fig:wideband']} and \ref{['fig:pessimistic']} would detect a system made of two black holes (each with an intrinsic mass $30\,\rm M_{\odot}$), as a function of redshift. Many systems of this sort will be detected at $z < 2$ with an ${\rm SNR} > 100$, enabling precision tests of gravity under the most extreme conditions.