In a new paper published today in Physical Review Letters we identify a class of modified theories of gravity where gravity is mediated by a scalar field coupled to quadratic terms in the curvature (the so-called “Gauss-Bonnet invariant”) that could be particularly interesting in the context of testing general relativity with gravitational wave detectors. These theories exhibit the phenomenon called “spontaneous scalarization” for both black holes and compact stars: for certain classes of solutions the scalar field can “grow” and modify the structure of these compact objects, with possible observational signatures. These theories formally admit all of the stationary solutions of general relativity, but the general relativistic solutions are not dynamically preferred if certain conditions are satisfied. Remarkably, black holes exhibit scalarization if their mass lies within one of many narrow bands.

Two related papers (one by Antoniou et al., the other by Doneva and Yazadjiev) appeared in the same issue of Physical Review Letters.