Spin-dependent scattering of boosted dark matter

Boosted dark matter is a promising method for probing light dark matter, with a well-developed computational framework for spin-independent scattering already existing. The spin-dependent case, on the other hand, lacks a coherent treatment. We therefore give the first comprehensive derivation of the spin -dependent scattering cross section for boosted dark matter, finding that certain effects can lead to enhanced experimental sensitivity compared to the conventional contact interaction. For example, when the transfer momentum is sufficiently large, the time component of the dark matter current contributes significantly to the proton structure factor. Also, even without a light mediator, we find a residual momentum dependence in the quark-nucleon matching operation that can contribute similarly. We promote this endeavor by deriving direct limits on sub-GeV spin-dependent scattering of boosted dark matter from terrestrial data. We find that the exclusion limits from the boosted structure factor differ by as much as six orders of magnitude from those calculated using nonrelativistic structure factors.

Automated summary

Boosted dark matter is a promising method to probe light dark matter, but the spin-dependent case lacks a coherent treatment. In this study, we derive the spin-dependent scattering cross section for boosted dark matter and find that certain effects can enhance experimental sensitivity. We also find that the time component of the dark matter current and the residual momentum dependence in the quark-nucleon matching operation contribute significantly. Direct limits on sub-GeV spin-dependent scattering of boosted dark matter are derived from terrestrial data, showing significant deviations from nonrelativistic structure factors.