Impact of Dark Compton Scattering on Direct Dark Matter Absorption Searches.

Direct detection experiments are gaining in mass reach. Here we show that the inclusion of dark Compton scattering, which has typically been neglected in absorption searches, has a substantial impact on the reach and discovery potential of direct detection experiments at high bosonic cold dark matter masses. We demonstrate this for relic dark photons and axionlike particles: we improve expected reach across materials, and further use results from SuperCDMS, EDELWEISS, and GERDA to place enhanced limits on dark matter parameter space. We outline the implications for detector design and analysis.

Determining Dark-Matter-Electron Scattering Rates from the Dielectric Function.

We show that the rate for dark-matter-electron scattering in an arbitrary material is determined by an experimentally measurable quantity, the complex dielectric function, for any dark matter interaction that couples to electron density. This formulation automatically includes many-body effects, eliminates all systematic theoretical uncertainties on the electronic wave functions, and allows a direct calibration of the spectrum by electromagnetic probes such as infrared spectroscopy, x-ray scattering, and electron energy-loss spectroscopy. Our formalism applies for several common benchmark models, including spin-independent interactions through scalar and vector mediators of arbitrary mass. We discuss the consequences for standard semiconductor and superconductor targets and find that the true reach of superconductor detectors for light mediators exceeds previous estimates by several orders of magnitude, with further enhancements possible due to the low-energy tail of the plasmon. Using a heavy-fermion superconductor as an example, we show how our formulation allows a rapid and systematic investigation of novel electron scattering targets.