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

Abstract

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 ${\ensuremath{\omega}}_{\mathrm{BD}}$. We show that gravitational-wave observations of nonspinning neutron star-black hole binary inspirals can be used to set lower bounds on ${\ensuremath{\omega}}_{\mathrm{BD}}$ and upper bounds on the combination ${m}_{s}/\sqrt{{\ensuremath{\omega}}_{\mathrm{BD}}}$. We estimate via a Fisher matrix analysis that individual observations with signal-to-noise ratio $\ensuremath{\rho}$ would yield $({m}_{s}/\sqrt{{\ensuremath{\omega}}_{\mathrm{BD}}})(\ensuremath{\rho}/10)\ensuremath{\lesssim}{10}^{\ensuremath{-}15}$, ${10}^{\ensuremath{-}16}$, and ${10}^{\ensuremath{-}19}\text{ }\text{ }\mathrm{eV}$ for Advanced LIGO, ET, and eLISA, respectively. A statistical combination of multiple observations may further improve these bounds.