Searching for ultralight dark matter with mechanical sensors

Abstract

The purpose of this dissertation is to assess the ability of tabletop devices, primarily based on mechanical systems, to serve as detectors for ultralight dark matter. ☐ Dark matter accounts for 85% of the matter in the Universe, yet its composition is unknown. One possibility is that dark matter is composed of ultralight particles with mass less than 10 eV/c2 (∼10-35kg), forming a coherent field. The ultralight dark matter field's non-gravitational interactions with normal matter would produce a weak, yet persistent, narrowband signal at an unknown frequency. This dissertation considers scenarios where dark matter is composed of novel spin 1 (vector) or spin 0 (scalar) particles whose interactions with normal matter result in measurable mechanical effects such as a strain or acceleration. Several prospective tabletop detectors are proposed, providing an avenue for small-scale experiments to contribute to the search for dark matter. ☐ First, various optomechanical resonators are proposed as detectors for ultralight dark matter. Specifically, silicon nitride optomechanical membranes are considered to search for vector ultralight dark matter, and several compact mechanical resonators composed of high-quality materials (superfluid and crystalline solids) are considered to search for scalar ultralight dark matter. Through a combination of low mechanical dissipation, cryogenic cooling, and cavity-enhanced optical readout, it is found that optomechanical resonators are capable of performing dark matter searches in the Hz-MHz frequency range, corresponding to particles of mass 10-12 - 10-6 eV/c2. ☐ As a broadband and low-frequency supplement to optomechanical resonators, whose mechanical resonances have limited bandwidth, an optical fiber-based detector is proposed to perform a broadband search for scalar ultralight dark matter. A case is made that, given sufficient cryogenic cooling and acoustic isolation, optical fiber-based detectors can be used to search for ultralight dark matter at sub-Hz frequencies (10-17- 10-13 eV/c2).