Fundamental Physics Implications for Higher-Curvature Theories from Binary Black Hole Signals in the LIGO-Virgo Catalog GWTC-1

Gravitational-wave astronomy offers not only new vistas into the realm of astrophysics, but it also opens an avenue for probing, for the first time, general relativity in its strong-field, nonlinear, and dynamical regime, where the theory’s predictions manifest themselves in their full glory. We present a study of whether the gravitational-wave events detected so far by the LIGO-Virgo scientific collaborations can be used to probe higher-curvature corrections to general relativity. In particular, we focus on two examples: Einstein-dilaton-Gauss-Bonnet and dynamical Chern-Simons gravity. We find that the two events with a low-mass $m\approx 7M_{\odot }$ BH (GW151226 and GW170608) place stringent constraints on Einstein-dilaton-Gauss-Bonnet gravity, ${\alpha }_{\mathrm{EDGB}}^{1/2}\lesssim 5.6\mathrm{km}$, whereas dynamical Chern-Simons gravity remains unconstrained by the gravitational-wave observations analyzed.

Figure 1

Posterior distributions of ${\alpha }_{\mathrm{DCS}}^{1/2}$ (left panel) and ${\alpha }_{\mathrm{EDGB}}^{1/2}$ (right panel) obtained using GW151226 and GW170608. For the GW events shown in both panels, $m_2/M_{\odot }=7.7_{-2.6}^{+2.2}$ (GW151226) and $m_2/M_{\odot }=7.6_{-2.1}^{+1.3}$ (GW170104) at 90% credibility. This implies that the small-coupling approximation is valid only when ${\alpha }_{\mathrm{DCS},\mathrm{EDGB}}^{1/2}\lesssim 5.6$, shown as vertical lines in the plots. For DCS gravity (left-panel) we see that most of the support of the posterior distributions of these two events lays passed the bounds set by the small-coupling approximation. Consequently, one cannot place constraints on ${\alpha }_{\mathrm{DCS}}^{1/2}$ with these two events. For EDGB gravity (right-panel) most ($>90\%$) of the support of the posteriors lays within the bound, therefore allowing us to constrain the theory with these two events. For the other three events, which contain a large $m_2$ ($\gtrsim 13M_{\odot }$) BH [30], the vertical lines are pushed towards the left, leaving most of the support for the posterior outside the small-coupling approximation bound. We stress that the location of the peaks in the posteriors are not an indication of a deviation from GR. Instead, as detailed in the main text, the lack of support at zero is an artifact of the choice of the sampling variable $\delta {\varphi }_i$.