No Arabic abstract
We present a detailed analysis of the effect of light Dark Matter (DM) on atomic clocks, for the case where DM mass and density are such that occupation numbers are low and DM must be considered as particles scattering off the atoms, rather than a classical field. We show that the resulting atomic clock frequency shifts are first order in the scattering amplitudes, and particularly suited to constrain DM models in the regime where the DM mass $m_chi ll$ GeV. We provide some rough order of magnitude estimates of sensitivity that can be confronted to any DM model that allows for non zero differential scattering amplitudes of the two atomic states involved in the clock.
Recent developments in searches for dark-matter candidates with atomic clocks are reviewed. The intended audience is the atomic clock community.
Particle dark matter could have a mass anywhere from that of ultralight candidates, $m_chisim 10^{-21},$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 $m_chisim 10^{-21}-10^3,$eV, depending on the model. We also comment on the (negligible) effect of different astrophysical neutrino backgrounds.
The cosmological applications of atomic clocks so far have been limited to searches of the uniform-in-time drift of fundamental constants. In this paper, we point out that a transient in time change of fundamental constants can be induced by dark matter objects that have large spatial extent, and are built from light non-Standard Model fields. The stability of this type of dark matter can be dictated by the topological reasons. We point out that correlated networks of atomic clocks, some of them already in existence, can be used as a powerful tool to search for the topological defect dark matter, thus providing another important fundamental physics application to the ever-improving accuracy of atomic clocks. During the encounter with a topological defect, as it sweeps through the network, initially synchronized clocks will become desynchronized. Time discrepancies between spatially-separated clocks are expected to exhibit a distinct signature, encoding defects space structure and its interaction strength with the Standard Model fields.
We study the mutual relationship between dark matter-electron scattering experiments and possible new dark matter substructure nearby hinted by the Gaia data. We show how kinematic substructure could affect the average and modulation spectra of dark matter-electron scattering in semiconductors, and the discovery reaches of future experiments with these targets. Conversely, we demonstrate how future data could probe and constrain the substructure dark matter fraction, even when it constitutes a sub-dominant component of the local dark matter density.
We present a novel mechanism for Sommerfeld enhancement for dark matter interactions without the need for light mediators. Considering a model for two-component scalar dark matter with a triple coupling, we find that there appears an $u$-channel resonance in dark matter elastic scattering. From the sum of the corresponding ladder diagrams, we obtain a Bethe-Salpeter equation with a delay term and identify the Sommerfeld factor for two-component dark matter from the effective Yukawa potential for the first time. We discuss the implications of our results for enhancing dark matter self-scattering and annihilation.