[Paper Review] Snowmass2021 Cosmic Frontier White Paper: Fundamental Physics and Beyond the Standard Model

Emanuele Berti, Vítor Cardoso+7 more|arXiv (Cornell University)|Mar 11, 2022

History and Developments in Astronomy9 citations

TL;DR

This Snowmass2021 Cosmic Frontier white paper proposes that gravitational wave (GW) observations from black hole and neutron star systems offer a transformative window into strong-field gravity and physics beyond the Standard Model. By leveraging third-generation Earth-based detectors, space-based missions like LISA, and pulsar timing arrays, the paper demonstrates how GWs can test general relativity, probe black hole horizons, detect ultralight bosons, constrain dark matter, and map cosmic expansion with multi-messenger data.

ABSTRACT

Gravitational wave detectors are formidable tools to explore strong-field gravity, especially black holes and neutron stars. These compact objects are extraordinarily efficient at producing electromagnetic and gravitational radiation. As such, they are ideal laboratories for fundamental physics and have an immense discovery potential. The detection of black hole binaries by third-generation Earth-based detectors, space-based detectors and pulsar timing arrays will provide exquisite tests of general relativity. Loud "golden" events and extreme mass-ratio inspirals can strengthen the observational evidence for horizons by mapping the exterior spacetime geometry, inform us on possible near-horizon modifications, and perhaps reveal a breakdown of Einstein's gravity. Measurements of the black-hole spin distribution and continuous gravitational-wave searches can turn black holes into efficient detectors of ultralight bosons across ten or more orders of magnitude in mass. A precise monitoring of the phase of inspiralling binaries can constrain the existence of additional propagating fields and characterize the environment in which the binaries live, bounding the local dark matter density and properties. Gravitational waves from compact binaries will probe general relativity and fundamental physics in previously inaccessible regimes, and allow us to address fundamental issues in our current understanding of the cosmos.

Motivation & Objective

• To assess the potential of gravitational wave detectors to test general relativity in the strong-field regime.
• To explore how black hole and neutron star systems can serve as laboratories for quantum gravity and the information paradox.
• To investigate the role of gravitational waves in detecting ultralight bosons and probing dark matter distributions.
• To use multi-messenger observations to constrain the Hubble constant and dark energy at high redshift.
• To examine the cosmological implications of primordial and cosmic string-generated gravitational waves.

Proposed method

• Utilizing third-generation ground-based detectors (e.g., Cosmic Explorer, Einstein Telescope) to detect high signal-to-noise ratio signals from stellar-mass binary black hole mergers.
• Applying space-based LISA to observe mHz-band gravitational waves from extreme mass-ratio inspirals and massive black hole binaries.
• Employing pulsar timing arrays to detect the stochastic gravitational wave background from supermassive black hole binaries.
• Analyzing the polarization, propagation speed, and symmetry properties of gravitational waves to test modifications of general relativity.
• Using black hole spectroscopy and horizon shadow mapping to probe near-horizon physics and test the existence of event horizons.
• Combining GW and electromagnetic data to constrain local dark matter density and detect non-perturbative effects from ultralight bosonic fields.

Experimental results

Research questions

• RQ1 Can gravitational wave observations from black hole binaries provide definitive tests of general relativity in the strong-field regime?
• RQ2 To what extent can gravitational waves reveal the presence of horizons or deviations from the Kerr metric?
• RQ3 Can gravitational wave signals constrain the existence of ultralight bosons via superradiance or resonant effects?
• RQ4 How precisely can multi-messenger observations using GWs and EM data measure the Hubble constant and dark energy evolution?
• RQ5 What are the detectable signatures of primordial gravitational waves from inflation or cosmic phase transitions?

Key findings

• Third-generation ground-based detectors will enable the observation of nearly all stellar-mass binary black hole mergers in the observable Universe, significantly improving signal-to-noise ratios.
• LISA will detect gravitational waves in the mHz band, allowing detailed mapping of extreme mass-ratio inspirals and probing the spacetime geometry around massive black holes.
• Pulsar timing arrays are on the verge of detecting the stochastic gravitational wave background from supermassive black hole binaries.
• Gravitational wave observations can constrain the mass of the graviton and test deviations in the propagation speed of GWs, with current data consistent with massless gravitons.
• Measurements of black hole spin distributions and continuous gravitational waves can probe the existence of ultralight bosons across more than ten orders of magnitude in mass.
• Precise phase monitoring of binary inspirals can bound the local dark matter density and constrain the properties of dark matter fields, including non-perturbative effects from ultralight bosonic condensates.