Cosmography with next-generation gravitational wave detectors (2402.03120v2)

Abstract: Advancements in cosmology through next-generation ground-based gravitational wave observatories will bring in a paradigm shift. We explore the pivotal role that gravitational-wave standard sirens will play in inferring cosmological parameters with next-generation observatories, not only achieving exquisite precision but also opening up unprecedented redshifts. We examine the merits and the systematic biases involved in gravitational-wave standard sirens utilizing binary black holes, binary neutron stars, and neutron star-black hole mergers. Further, we estimate the precision of bright sirens, golden dark sirens, and spectral sirens for these binary coalescences and compare the abilities of various next-generation observatories (A^sharp, Cosmic Explorer, Einstein Telescope, and their possible networks). When combining different sirens, we find sub-percent precision over more than 10 billion years of cosmic evolution for the Hubble expansion rate $H(z)$. This work presents a broad view of opportunities to precisely measure the cosmic expansion rate, decipher the elusive dark energy and dark matter, and potentially discover new physics in the uncharted Universe with next-generation gravitational-wave detectors.

• The paper demonstrates that next-generation gravitational wave detectors can use standard sirens to achieve sub-percent precision in measuring cosmic expansion over vast redshifts.
• The study integrates bright sirens from EM counterparts with dark and spectral sirens to address systematic biases and improve cosmological measurements.
• The findings forecast that combining multiple GW probe techniques will resolve existing tensions in estimating key cosmological parameters.

Cosmography with Next-Generation Gravitational Wave Detectors

The paper "Cosmography with next-generation gravitational wave detectors" by Hsin-Yu Chen, Jose Maria Ezquiaga, and Ish Gupta provides a comprehensive analysis of the enhanced capabilities that future gravitational wave (GW) observatories will provide in the field of cosmology. The authors discuss the significant role that gravitational-wave standard sirens will play in refining the inference of cosmological parameters, exploring the vast spans of redshift that next-generation observatories will access. The paper provides insights into the methodologies and projections surrounding these advancements, including the analysis of systematic biases and the synthesis of bright and dark sirens from binary black holes, binary neutron stars, and neutron star-black hole mergers.

Summary of Methodologies

The paper delineates several methodologies for acquiring cosmic information via gravitational-wave standard sirens:

1. Gravitational Wave Source Types: The analysis initially classifies gravitational wave sources into binary black holes, binary neutron stars, and neutron star-black hole mergers. Each type provides unique data for cosmological inference, and the precise waveform predictions inherent to general relativity enable their use as standard sirens.
2. Utilization of Bright Sirens: By observing EM counterparts to GW events, such as kilonovae associated with neutron star mergers, one can acquire redshift information necessary for precise cosmological measurements. The paper discusses statistical techniques to counter systematic biases in redshift determination, instrumental calibration, and host peculiar velocities.
3. Dark Sirens and Population Statistics: Investigating sources with undetected EM counterparts, known as dark sirens, is emphasized. The authors consider statistical techniques using galaxy catalogs and cross-correlations with large-scale structures to acquire redshift data. Despite larger uncertainties than bright sirens, they offer a pivotal measurement opportunity, notably with golden dark sirens.
4. Spectral Sirens: The population mass spectrum is evaluated to gauge redshift, based on shifts in the detected mass distributions at different redshifted luminosity distances. This allows for the exploration of the Universe's expansion rate history with remarkable precision using the full catalog of detected events.

Results and Implications

The authors highlight robust numerical findings and make several forecasts:

• Precision in H(z) Measurement: Next-generation detectors like Cosmic Explorer and the Einstein Telescope promise sub-percent accuracy for estimating the Hubble parameter H(z) across more than 10 billion years of cosmic history, breaking new ground in cosmology's effort to decipher dark energy and dark matter influences.
• Extreme Sensitivity and Detection Range: The vast sensitivity of these detectors aims at observing events up to redshifts of approximately 100, encompassing the full spectrum of stellar-mass black holes across the Universe and reaching prior regions dominated by dark matter.
• Combining Probe Techniques: The synergy of different standard sirens—amalgamating bright, dark, and spectral sirens—is anticipated to resolve existing tensions among electromagnetic-based cosmological measurements and gravitational waves.

Future Developments

The paper concludes by considering the theoretical and practical future implications of gravitational-wave astrophysics:

• Increased Data Synthesis and Systematic Uncertainties: The expansive new data from forthcoming detector networks demands innovative analysis techniques and thorough treatment of systematic uncertainties. The use of enhanced precision in population synthesis models and non-parametric reconstructions is essential for valid cosmographical results.
• Integration of Cosmological Frameworks: The potential to test alternative cosmological models, such as those involving dynamic dark energy or modifications of general relativity on large scales, will significantly benefit from these enhanced observational capabilities, allowing us to test new aspects of our Universe.

In conclusion, this paper paints an insightful picture of a future where gravitational wave detectors extend our reach into the far corners of the Universe, profoundly impacting our understanding of its expansion and the underlying cosmological models. While methodical in its analysis, it promises an exciting frontier for gravitational wave astronomy and its intersection with cosmology.