An optical fiber-based detector for scalar ultralight dark matter

We discuss a potential broadband search for scalar ultralight dark matter (ULDM) with an optical fiber-based detector. ULDM that couples to electrons and/or photons would cause oscillations in the electron mass and fine structure constant, both of which produce measurable signals: isotropic strains and varying optical refractive indices. These signals are approximately monochromatic, with an unknown frequency determined by the ULDM particle mass. Both strains and refractive index modulation induce phase shifts in light propagating through optical fibers, which can be read out interferometrically. We show that optical fibers can be used to perform a laboratory-scale, broadband search for scalar ULDM in the relatively unexplored sub-Hz frequency regime (corresponding to ~10^-16-10^-15 eV/c² particle mass).