Direct detection of bound states of asymmetric dark matter

Abstract

We study the reach of direct detection experiments for large bound states (containing 10⁴ or more dark nucleons) of asymmetric dark matter. We consider ordinary nuclear recoils, excitation of collective modes (phonons), and electronic excitations, paying careful attention to the impact of the energy threshold of the experiment. Large exposure experiments with keV energy thresholds provide the best (future) limits when the dark matter is small enough to be treated as a point particle, but rapidly lose sensitivity for more extended dark bound states, or when the mediator is light. In those cases, low threshold, low exposure experiments (such as with a superfluid helium, polar material or superconducting target) are often more sensitive due to coherent enhancement over the dark nucleons. We also discuss indirect constraints on composite asymmetric dark matter arising from self-interaction, formation history, and the properties of the composite states themselves.