Constraining spontaneous black hole scalarization in scalar-tensor-Gauss-Bonnet theories with current gravitational-wave data

Abstract

We examine the constraining power of current gravitational-wave data on scalar-tensor-Gauss-Bonnet theories that allow for the spontaneous scalarization of black holes. In the fiducial model that we consider, a slowly rotating black hole must scalarize if its size is comparable to the new length scale $\ensuremath{\lambda}$ that the theory introduces, although rapidly rotating black holes of any mass are effectively indistinguishable from their counterparts in general relativity. With this in mind, we use the gravitational-wave event GW190814---whose primary black hole has a spin that is bounded to be small, and whose signal shows no evidence of a scalarized primary---to rule out a narrow region of the parameter space. In particular, we find that values of $\ensuremath{\lambda}\ensuremath{\in}[56,96]\text{ }\text{ }{M}_{\ensuremath{\bigodot}}$ are strongly disfavored with a Bayes factor of 0.1 or less. We also include a second event, GW151226, in our analysis to illustrate what information can be extracted when the spins of both components are poorly measured.