Parametrized tests of post-Newtonian theory using Advanced LIGO and Einstein Telescope

TL;DR

This paper explores how advanced gravitational wave detectors like LIGO and ET can measure post-Newtonian coefficients to test general relativity and constrain alternative theories, using high-accuracy waveform models.

Contribution

It demonstrates the potential of second and third generation detectors to test specific PN terms and parametrize deviations from general relativity in inspiral waveforms.

Findings

LIGO can test the 1.5PN tail term in gravitational wave phase.

ET can verify consistency of PN coefficients across 11-44 solar mass binaries.

Lower frequency cutoff significantly affects the testing capability.

Abstract

General relativity has very specific predictions for the gravitational waveforms from inspiralling compact binaries obtained using the post-Newtonian (PN) approximation. We investigate the extent to which the measurement of the PN coefficients, possible with the second generation gravitationalwave detectors such as the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) and the third generation gravitational-wave detectors such as the Einstein Telescope (ET), could be used to test post-Newtonian theory and to put bounds on a subclass of parametrized-post-Einstein theories which differ from general relativity in a parametrized sense. We demonstrate this possibility by employing the best inspiralling waveform model for nonspinning compact binaries which is 3.5PN accurate in phase and 3PN in amplitude. Within the class of theories considered, Advanced LIGO can test the theory at 1.5PN and thus the leading tail term. Future observations of stellar mass black hole binaries by ET can test the consistency between the various PN coefficients in the gravitational-wave phasing over the mass range of 11-44 Msun. The choice of the lower frequency cut off is important for testing post-Newtonian theory using the ET. The bias in the test arising from the assumption of nonspinning binaries is indicated.