Exploring the ultra-light to sub-MeV dark matter window with atomic clocks and co-magnetometers

TL;DR

This paper investigates how atomic clocks and co-magnetometers can detect ultra-light to sub-MeV dark matter that interacts via spin coupling, extending the search to mass ranges difficult for traditional methods.

Contribution

It introduces experimental setups that do not require momentum transfer, providing new constraints on dark matter models in the ultra-light to sub-MeV mass range.

Findings

Current atomic clocks and co-magnetometers can constrain dark matter in the mass range 10^{-21} to 10^3 eV.

These techniques are competitive with existing methods for certain dark matter models.

Astrophysical neutrino backgrounds have negligible impact on these measurements.

Abstract

Particle dark matter could have a mass anywhere from that of ultralight candidates, $m_\chi\sim 10^{-21}\,$eV, to scales well above the GeV. Conventional laboratory searches are sensitive to a range of masses close to the weak scale, while new techniques are required to explore candidates outside this realm. In particular lighter candidates are difficult to detect due to their small momentum. Here we study two experimental set-ups which {\it do not require transfer of momentum} to detect dark matter: atomic clocks and co-magnetometers. These experiments probe dark matter that couples to the spin of matter via the very precise measurement of the energy difference between atomic states of different angular momenta. This coupling is possible (even natural) in most dark matter models, and we translate the current experimental sensitivity into implications for different dark matter models. It is found that the constraints from current atomic clocks and co-magnetometers can be competitive in the mass range $m_\chi\sim 10^{-21}-10^3\,$eV, depending on the model. We also comment on the (negligible) effect of different astrophysical neutrino backgrounds.