[Paper Review] Extreme Gravity and Fundamental Physics

B. S. Sathyaprakash, Alessandra Buonanno+27 more|arXiv (Cornell University)|Mar 21, 2019

Pulsars and Gravitational Waves Research106 references43 citations

TL;DR

The Astro2020 science white paper surveys how future gravitational-wave observations, especially with 3G detectors, can probe gravity, dark matter, and the nature of compact objects, outlining theoretical frameworks and observational signatures of new physics beyond General Relativity.

ABSTRACT

Future gravitational-wave observations will enable unprecedented and unique science in extreme gravity and fundamental physics answering questions about the nature of dynamical spacetimes, the nature of dark matter and the nature of compact objects.

Motivation & Objective

• Motivation to test the nature of gravity and fundamental physics in extreme gravity environments.
• Assess how gravitational waves probe strong-field gravity and potential deviations from General Relativity.
• Explore implications for dark matter candidates and the nature of compact objects like black holes and neutron stars.
• Identify theoretical frameworks (scalar-tensor theories, Lorentz/parity violations, beyond-GR compact objects) that yield observable signatures.
• Outline the role of next-generation detectors (3G) in transforming understanding of high-curvature regimes.

Proposed method

• Review of current gravitational-wave detections (GW150914, GW170817) and their implications for GR tests.
• Discussion of beyond-GR theories and their predicted signatures in waves (scalar fields, extra polarizations, dipole radiation, modified dispersion).
• Analysis of dark matter scenarios involving black holes, neutron stars, and environmental effects on GW signals.
• Consideration of exotic compact objects and their quasi-normal modes as tests of the Kerr metric.
• Projection of 3G detector capabilities to constrain graviton mass, Lorentz and parity violations, and ultralight bosons via gravitational-wave observations.

Experimental results

Research questions

• RQ1 Can gravitational-wave observations test the validity of General Relativity in dynamical spacetimes?
• RQ2 What signatures in waves indicate departures from GR (e.g., extra polarizations, dipole radiation, dispersion, birefringence) and how detectable are they?
• RQ3 What do GW observations imply about dark matter candidates and their interactions with compact objects?
• RQ4 How can 3G detectors constrain new physics such as massive gravitons, Lorentz violation, and ultralight bosons through compact-binary events?
• RQ5 What exotic compact objects or horizon-scale phenomena could be revealed by future GW signals?

Key findings

• Gravitational waves carry uncorrupted signatures from strong-field gravity and enable tests of GR in dynamical spacetimes.
• 3G detectors are expected to constrain graviton mass and Lorentz-violating effects by observing high-redshift sources and precise waveforms.
• GW observations can probe dark matter through effects on binary dynamics and possible accretion/drag in dark-matter environments.
• Future detectors will measure neutron-star equations of state and tidal effects with improved precision, informing dense-matter physics.
• Exotic compact objects (e.g., boson stars, gravastars) may imprint distinct quasi-normal modes or ringdown signals differing from Kerr black holes, testable by 3G detectors.
• Ultralight bosons and superradiance could leave observable imprints in spin distributions and continuous GW signals from black holes.