  We show that proton storage ring experiments designed to search for proton
electric dipole moments can also be used to look for the nearly dc spin
precession induced by dark energy and ultra-light dark matter. These
experiments are sensitive to both axion-like and vector fields. Current
technology permits probes of these phenomena up to three orders of magnitude
beyond astrophysical limits. The relativistic boost of the protons in these
rings allows this scheme to have sensitivities comparable to atomic
co-magnetometer experiments that can also probe similar phenomena. These
complementary approaches can be used to extract the micro-physics of a signal,
allowing us to distinguish between pseudo-scalar, magnetic and electric dipole
moment interactions.
