Listening for ultra-heavy dark matter with underwater acoustic detectors

Abstract

Ultra-heavy dark matter candidates evade traditional direct detection experiments due to their low particle flux. We explore the potential of large underwater acoustic arrays, originally developed for ultra-high energy neutrino detection, to detect ultra-heavy dark matter interactions. These particles deposit energy via nuclear scattering while traversing seawater, generating thermo-acoustic waves detectable by hydrophones. We present the first robust first-principles calculation of dark matter-induced acoustic waves, establishing a theoretical framework for signal modelling and sensitivity estimates. Our framework incorporates frequency-dependent attenuation effects, including viscous and chemical relaxation, not considered in previous calculations. A sensitivity analysis for a hypothetical 100 cubic kilometre hydrophone array in the Mediterranean Sea demonstrates that such an array could extend sensitivity to the previously unexplored mass range of $0.1$-$10\,\mu\mathrm{g}$ ($\sim10^{20}$-$10^{23}\,\mathrm{GeV}$), with sensitivity to both spin-independent and spin-dependent interactions. Our results establish acoustic detection as a complementary dark matter search method, enabling searches in existing hydrophone data and informing future detector designs.