TESTING SCALAR-TENSOR GRAVITY WITH GRAVITATIONAL-WAVE OBSERVATIONS OF INSPIRALLING COMPACT BINARIES

Observations of gravitational waves from inspiralling compact binaries using laser-interferometric detectors can provide accurate measures of parameters of the source. They can also constrain alternative gravitation theories. We analyze inspiralling compact binaries in the context of the scalar-tensor theory of Jordan, Fierz, Brans, and Dicke, focusing on the effect on the inspiral of energy lost to dipole gravitational radiation, whose source is the gravitational self-binding energy of the inspiralling bodies. Using a matched-filter analysis we obtain a bound on the coupling constant BD of Brans-Dicke theory. For a neutron-star black-hole binary, we find that the bound could exceed the current bound of BD>500 from solar-system experiments, for sufficiently low-mass systems. For a 0.7M neutron star and a 3M black hole we find that a bound BD 2000 is achievable. The bound decreases with increasing black-hole mass. For binaries consisting of two neutron stars, the bound is less than 500 unless the stars masses differ by more than about 0.5M. For two black holes, the behavior of the inspiralling binary is observationally indistinguishable from its behavior in general relativity. These bounds assume reasonable neutron-star equations of state and a detector signal-to-noise ratio of 10. © 1994 The American Physical Society.