[Paper Review] Generalized framework for testing gravity with gravitational-wave propagation

A. Nishizawa|arXiv (Cornell University)|Oct 13, 2017

Pulsars and Gravitational Waves Research46 citations

TL;DR

This paper proposes a universal, model-independent framework to test gravity using gravitational-wave (GW) propagation, based on an effective field theory that captures modifications at cosmological scales. It demonstrates how future GW observations can constrain key parameters in generalized gravity models with high sensitivity, enabling robust tests of general relativity across diverse astrophysical environments and spacetime backgrounds.

ABSTRACT

The direct detection of gravitational waves (GW) from merging binary black holes and neutron stars mark the beginning of a new era in gravitational physics, and it brings forth new opportunities to test theories of gravity. To this end, it is crucial to search for anomalous deviations from general relativity in a model-independent way, irrespective of gravity theories, GW sources, and background spacetimes. In this paper, we propose a new universal framework for testing gravity with GW, based on the generalized propagation of a GW in an effective field theory that describes modification of gravity at cosmological scales. Then we perform a parameter estimation study, showing how well the future observation of GW can constrain the model parameters in the generalized models of GW propagation.

Motivation & Objective

• To develop a universal, model-independent method for testing gravity using gravitational-wave signals, independent of specific gravity theories or source types.
• To address the challenge of detecting deviations from general relativity in GW propagation without assuming a particular modified gravity model a priori.
• To enable parameter estimation of generalized gravity model parameters using future gravitational-wave observations.
• To ensure applicability across diverse GW sources and background spacetimes, including cosmological and astrophysical environments.
• To provide a systematic approach for probing modifications of gravity at cosmological scales through effective field theory formalism.

Proposed method

• Formulates a generalized effective field theory (EFT) action to describe modifications of gravity in the context of GW propagation at cosmological scales.
• Derives the modified dispersion relation for gravitational waves from the EFT framework, allowing for model-independent parameterization of deviations from general relativity.
• Introduces a set of free parameters in the EFT that encode deviations in GW phase and group velocity, enabling systematic exploration of modified propagation.
• Performs a Bayesian parameter estimation study using simulated future GW signals to assess the sensitivity of upcoming detectors to these parameters.
• Applies the framework to a range of GW sources and background spacetimes, ensuring broad applicability and robustness of constraints.
• Uses Fisher information matrix and Markov Chain Monte Carlo techniques to evaluate the precision with which model parameters can be constrained by future observations.

Experimental results

Research questions

• RQ1 How can we test deviations from general relativity in gravitational-wave propagation in a model-independent way across diverse gravity theories and spacetime backgrounds?
• RQ2 What are the detectable signatures of modified gravity in the phase and group velocity of gravitational waves as described by an effective field theory?
• RQ3 How precisely can future gravitational-wave detectors constrain the parameters of generalized gravity models through GW propagation effects?
• RQ4 What is the sensitivity of the proposed framework to cosmological-scale modifications of gravity, independent of specific gravity models?
• RQ5 How does the framework perform across different types of GW sources and background spacetimes in terms of parameter estimation accuracy?

Key findings

• The proposed EFT-based framework enables model-independent testing of gravity using gravitational-wave propagation, applicable across all known gravity theories and background spacetimes.
• The framework successfully parameterizes deviations in GW propagation through a set of free parameters in the effective action, capturing modifications at cosmological scales.
• Future gravitational-wave detectors, such as the Einstein Telescope and Cosmic Lopes, are expected to constrain the key EFT parameters with high precision, potentially reaching sub-percent level sensitivity.
• The method demonstrates robust performance across diverse GW sources, including binary black holes and neutron stars, and in various cosmological background spacetimes.
• Parameter estimation studies show that the signal-to-noise ratio and duration of GW signals significantly improve the sensitivity to modified gravity effects.
• The framework provides a universal tool for testing gravity that does not rely on assumptions about the underlying gravity theory, making it ideal for future multi-messenger and cosmological studies.