New Limits on the Couplings of Light Pseudoscalars from Equivalence Principle Experiments

The exchange of light pseudoscalar quanta between fermions leads to long-range spin-dependent forces in order $g^2$, where $g$ is the pseudoscalar-fermion coupling constant. We demonstrate that laboratory bounds on the Yukawa couplings of pseudoscalars to nucleons can be significantly improved using results from recent equivalence principle experiments, which are sensitive to the spin-independent long-range forces that arise in order $g^4$ from two-pseudoscalar exchange.