Searching for Scalar Dark Matter with Compact Mechanical Resonators.

Ultralight scalars are an interesting dark matter candidate that may produce a mechanical signal by modulating the Bohr radius. Recently it has been proposed to search for this signal using resonant-mass antennas. Here, we extend that approach to a new class of existing and near term compact (gram to kilogram mass) acoustic resonators composed of superfluid helium or single crystal materials, producing displacements that are accessible with opto- or electromechanical readout techniques. We find that a large unprobed parameter space can be accessed using ultrahigh-Q, cryogenically cooled centimeter-scale mechanical resonators operating at 100 Hz-100 MHz frequencies, corresponding to 10^{-12}-10^{-6}  eV scalar mass range.