Gravitational Wave Probes of Modified Gravity: A new Tool for testing Cosmological Models

Abstract

Gravitational-wave (GW) observation has opened up a new array of information on the universe by adding information that has been obtained from electromagnetic and particle astronomy observations. Not only can physicists develop further confidence in Einstein’s General Relativity(GR) through GW’s, but GW’s can also be used to conduct ‘tests’ on alternative theories of gravity that have previously been unimaginable or impossible to test. Many of these theories of modified gravity (MG), which have been suggested to explain the apparent acceleration of the cosmos and the nature of dark matter, or provide an explanation for deficiencies in the Standard Model, predict that GW’s would have fundamental differences in the way they are produced, and the way they propagate through space-time, as well as differences in their polarization. In this article, we discuss how current and future GW data can provide a means of testing such MG theories. We provide a brief overview of the theoretical constraints and the most recent published results from the LIGO-Virgo-KAGRA collaboration, as well as discussing an upcoming way to evaluate cosmological models via GW propagation effects and multi-messenger detection, along with likely deviations in waveform characteristics. Our analysis indicates that by using future detectors, such as LISA and the Einstein Telescope, MG parameter constraints will be greatly reduced, thereby providing a means to unequivocally differentiate GR from alternative gravitational frameworks.