Long-range axion forces and hadronic CP violation

Axions and other pseudoscalar fields comprise an interesting class of ultralight dark matter candidates, that may independently play a role in solving the strong CP problem. In the presence of CP-violating sources, these pseudoscalar fields can develop a coherent nonderivative coupling to nucleons, g over bar aNN, thus mediating 'mass-mass' and 'mass-spin' forces in matter that can be probed experimentally. We revisit the nonperturbative generation of these CP-odd axion forces, and refine estimates of g over bar aNN generated by the electric dipole moments and color electric dipole moments of quarks. We also revisit the Standard Model contribution to CP-odd axion couplings generated by the phase of the Cabibbo-KobayashiMaskawa quark mixing matrix.

Automated summary

Axions and other pseudoscalar fields are candidates for ultralight dark matter that can solve the strong CP problem and be detectable through experiments. This study revisits the generation mechanism of these axion forces and improves upon the estimation of their strengths.