Listening for ultraheavy dark matter with underwater acoustic detectors

Ultraheavy 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 ultrahigh energy neutrino detection, to detect ultraheavy dark matter interactions. These particles deposit energy via nuclear scattering while traversing seawater, generating thermoacoustic waves detectable by hydrophones. We present the first robust first-principles calculation of dark matter-induced acoustic waves, establishing a theoretical framework for signal modeling 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 100km3 hydrophone array in the Mediterranean Sea demonstrates that such an array could extend sensitivity to the previously unexplored mass range of 0.1−10 μg (∼1020–1023 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.