Black Hole Binaries in Cubic Horndeski Theories

TL;DR

This paper investigates black hole binary mergers within cubic Horndeski theories, revealing significant waveform deviations from general relativity that could impact gravitational wave observations.

Contribution

It provides the first fully non-linear numerical simulations of black hole mergers in cubic Horndeski theories, quantifying waveform differences from GR.

Findings

Waveform mismatch can reach 10-13% in the LIGO frequency band.

Waveform shifts are larger than the small coupling parameter, indicating strong effects.

The effects are generic and may appear in other higher-derivative gravity theories.

Abstract

We study black hole binary mergers in certain cubic Horndeski theories of gravity, treating them fully non-linearly. In the regime of validity of effective field theory, the mismatch of the gravitational wave strain between Horndeski and general relativity (coupled to a scalar field) can be as large as $10-13\%$ in the Advanced LIGO mass range. The initial data and coupling constants are chosen such the theory remains in the weakly coupled regime throughout the evolution. In all cases that we have explored, we observe that the waveform in the Horndeski theory is shifted by an amount much larger than the smallness parameter that controls the initial data. This effect is generic and may be present in other theories of gravity involving higher derivatives.