Bosonic Dark Matter Searches with Precision Instruments

If the dark matter is made up of a bosonic particle, it can be ultralight, with a mass potentially much below that of ordinary particles. Moduli fields, whose values could set couplings and masses of known particles, are good candidates for such light dark matter. Their abundance in our Universe would manifest itself as tiny fractional oscillations of Standard Model parameters, such as the electron mass or the fine-structure constant, in turn modulating length and time scales of atoms. Rods and clocks, used for gedanken experiments in the development of relativity theory, have since transformed into actual precision instruments. The size of acoustic resonators and the frequency of atomic transitions can now be measured to 1 part in 10^24 and 10^18, respectively, and thus constitute sensitive probes of moduli over a mass range of 10^-22 eV to 10^-6 eV.