Improved bounds on ultralight scalar dark matter in the radio-frequency range

Abstract

We present a search for fundamental constant oscillations in the range 20 kHz–100 MHz that may arise within models for ultralight dark matter (UDM). Using two independent optical-spectroscopy apparatuses, we achieve up to × 1000 greater sensitivity in the search relative to previous work [D. Antypas et al., Phys. Rev. Lett. 123, 141102 (2019).]. We report no observation of UDM and thus constrain respective couplings to electrons and photons within the investigated UDM particle mass range 8 × 10 − 11 – 4 × 10 − 7 eV . The constraints significantly exceed previously set bounds from atomic spectroscopy and, as we show, may surpass in future experiments those provided by equivalence-principle (EP) experiments in a specific case regarding the combination of UDM couplings probed by the EP experiments.