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

TL;DR

This paper uses current gravitational-wave data to constrain scalar-tensor-Gauss-Bonnet theories that predict black hole scalarization, ruling out certain parameter ranges and demonstrating the method's effectiveness.

Contribution

It provides the first observational constraints on scalar-tensor-Gauss-Bonnet theories allowing black hole scalarization using gravitational-wave data.

Findings

Values of λ between 56 and 96 solar masses are strongly disfavored.

Current GW data can effectively constrain scalarization parameters.

Analysis shows the importance of spin measurements in testing these theories.

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 $\lambda$ 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$\,\unicode{x2014}\,$whose primary black hole has a spin that is bounded to be small, and whose signal shows no evidence of a scalarized primary$\,\unicode{x2014}\,$to rule out a narrow region of the parameter space. In particular, we find that values of ${\lambda \in [56, 96]~M_\odot}$ 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.