Light scalar field constraints from gravitational-wave observations of compact binaries

Scalar-tensor theories are among the simplest extensions of general relativity. In theories with light scalars, deviations from Einstein's theory of gravity are determined by the scalar mass m(s) and by a Brans-Dicke-like coupling parameter omega(BD). We show that gravitational-wave observations of nonspinning neutron star-black hole binary inspirals can be used to set lower bounds on omega(BD) and upper bounds on the combination m(s)/root omega(BD). We estimate via a Fisher matrix analysis that individual observations with signal-to-noise ratio rho would yield (m(s)/root omega(BD))(rho/10) less than or similar to 10(-15), 10(-16), and 10(-19) eV for Advanced LIGO, ET, and eLISA, respectively. A statistical combination of multiple observations may further improve these bounds.