Gravitational waves from extreme gravity events such as the coalescence of two black holes in a binary system fill our observable Universe, bearing with them the underlying theory of gravity driving their process. One compelling alternative theory of gravity—known as Einstein-dilaton Gauss-Bonnet gravity motivated by string theory—describes the presence of an additional dilaton scalar field coupled directly to higher orders of the curvature, effectively describing a “fifth force” interaction and the emission of scalar dipole radiation between two scalarized black holes. Most previous studies focused on considering only the leading correction to the inspiral portion of the binary black hole waveforms. In our recent paper, we carried out inspiral-merger-ringdown consistency tests in this string-inspired gravity by including corrections to both the inspiral and ringdown portions, as well as those to the mass and spin of remnant black holes, valid to quadratic order in spin. We here extend the analysis by directly computing bounds on the theoretical coupling constant using the full inspiral-merger-ringdown waveform rather than treating the inspiral and merger-ringdown portions separately. We also consider the corrections valid to quartic order in spin to justify the validity of black hole’s slow-rotation approximation. We find the quasinormal mode corrections to the waveform to be particularly important for high-mass events such as GW170729, in which the dilaton fields’ small-coupling approximation fails without such effects included. We also show that future space-based and multiband gravitational-wave observations have the potential to go beyond existing bounds on the theory. The bounds presented here are comparable to those found via the inspiral-merger-ringdown consistency tests.

• Received 29 February 2020
• Accepted 6 May 2020

DOI:https://doi.org/10.1103/PhysRevD.101.104030