Probing dipole radiation from binary neutron stars with ground-based laser-interferometer and atom-interferometer gravitational-wave observatories

Abstract

Atom-interferometer gravitational-wave (GW) observatories, as a new design of ground-based GW detectors due in the near future, are sensitive at a relatively low frequency for GW observations. Taking the proposed atom interferometer Zhaoshan long-baseline Atom Interferometer Gravitation Antenna (ZAIGA), and its illustrative upgrade ($\mathrm{Z}+$) as examples, we investigate how the atom interferometer will complement ground-based laser interferometers in testing the gravitational dipole radiation from binary neutron star (BNS) mergers. A test of this kind is important for a better understanding of the strong equivalence principle lying at the heart of Einstein's general relativity. To obtain a statistically sound result, we sample BNS systems according to their merger rate and population, from which we study the expected bounds on the parametrized dipole-radiation parameter $B$. Extracting BNS parameters and the dipole radiation from the combination of ground-based laser interferometers and the atom interferometer $\mathrm{ZAIGA}/\mathrm{Z}+$, we are entitled to obtain tighter bounds on $B$ by a few times to a few orders of magnitude, compared to ground-based laser interferometers alone, ultimately reaching the levels of $|B|\ensuremath{\lesssim}{10}^{\ensuremath{-}9}$ (with ZAIGA) and $|B|\ensuremath{\lesssim}{10}^{\ensuremath{-}10}$ (with $\mathrm{Z}+$).