Searching for dark clumps with gravitational-wave detectors

Abstract

Dark compact objects (``clumps'') transiting the Solar System exert accelerations on the test masses (TM) in a gravitational-wave (GW) detector. We reexamine the detectability of these clump transits in a variety of current and future GW detectors, operating over a broad range of frequencies. TM accelerations induced by clump transits through the inner Solar System have frequency content around $f\ensuremath{\sim}\ensuremath{\mu}\mathrm{Hz}$. Some of us [Fedderke et al., Phys. Rev. D 105, 103018 (2022)] recently proposed a GW detection concept with $\ensuremath{\mu}\mathrm{Hz}$ sensitivity, based on asteroid-to-asteroid ranging. From the detailed sensitivity projection for this concept, we find both analytically and in simulation that purely gravitational clump--matter interactions would yield one detectable transit every $\ensuremath{\sim}20\text{ }\text{ }\mathrm{yrs}$, if clumps with mass ${m}_{\mathrm{cl}}\ensuremath{\sim}{10}^{14}\text{ }\text{ }\mathrm{kg}$ saturate the dark-matter (DM) density. Other (proposed) GW detectors using local TMs and operating in higher frequency bands are sensitive to smaller clump masses and have smaller rates of discoverable signals. We also consider the case of clumps endowed with an additional attractive long-range clump--matter fifth force significantly stronger than gravity (but evading known fifth-force constraints). For the $\ensuremath{\mu}\mathrm{Hz}$ detector concept, we use simulations to show that, for example, a clump--matter fifth-force $\ensuremath{\sim}{10}^{3}$ times stronger than gravity with a range of $\ensuremath{\sim}\mathrm{AU}$ would boost the rate of detectable transits to a few per year for clumps in the mass range ${10}^{11}\text{ }\text{ }\mathrm{kg}\ensuremath{\lesssim}{m}_{\mathrm{cl}}\ensuremath{\lesssim}{10}^{14}\text{ }\text{ }\mathrm{kg}$, even if they are a $\ensuremath{\sim}1%$ subcomponent of the DM. The ability of $\ensuremath{\mu}\mathrm{Hz}$ GW detectors to probe asteroid-mass-scale dark objects that may otherwise be undetectable bolsters the science case for their development.