Direct Search for Scalar Field Dark Matter with the Fermilab Holometer

Introduction. - Cosmological modeling suggests that 'dark matter' (DM) comprises a large fraction of the total matter content of the universe, but its origin and physical properties remain unknown to date. Although indirect astronomical observations in the last few decades seem to confirm its existence, a first direct detection of dark matter is still missing, and it represents one of the greatest challenges of contemporary physics. In scenarios where a low-mass scalar field constitutes DM, the field can couple to interferometric detectors, which then produce a signal. This prediction can be used to search for DM signals, and if no signal is detected, constraints on the DM parameters can be placed. Recent examples of this new type of DM search have involved gravitational wave detectors: GEO 600 [1] for scalar field DM [2,3] and Advanced LIGO and Advanced VIRGO [4,5] for dark photon DM [6]. Thanks to technological progress, these precision interferometers can now reach sensitivities to length variations at or beyond quantum limits, and they can be used in contexts different from the ones for which they were originally developed. In this work, we perform a direct search for scalar field DM using the data from the Fermilab Holometer instrument [7,8], which consists of twin Michelson interferometers. Its cross-correlation sensitivity in the 1-25 MHz frequency range allows us to set new upper limits on the coupling parameters of scalar field DM in a different DM mass range from the one already constrained by the GEO 600 interferometer and other experiments.

Theory. - The work presented in this letter concerns low-mass (mφ << 1 eV) DM models. In this scenario, the DM is represented by a scalar field φ of mass mφ, which couples with the standard model (SM) fields. The coupling is parameterized through the addition of an interaction term in the SM Lagrangian [3,9].