Using Earth to Search for Long-Range Spin-Velocity Interactions

Precision measurements of the possible coupling of spin to other scalars, vectors and pseudovectors has proven to be a sensitive way to search for new particle physics beyond the standard model. Indeed, in addition to searching for exotic spin-spin interactions, studies have been undertaken to look for couplings of spin to gravity, the relative velocity between particles, and preferred directions. Several laboratory experiments have established upper bounds on the energy associated with various fermion spin-orientations relative to Earth. Here, we combine these results with a model of Earth in order to investigate the possible long-range spin-velocity interactions associated with the exchange of ultralight ($m_{z'}<1$ neV) or massless scalar or vector bosons. We establish stringent bounds on the strength of these couplings between electrons, neutrons, protons and nucleons.