Oscillating nuclear electric dipole moment induced by axion dark matter produces atomic and molecular EDM

Abstract

According to the Schiff theorem nuclear electric dipole moment (EDM) is completely shielded in a neutral atom by electrons. This makes a static nuclear electric dipole moment (EDM) unobservable. Interaction with the axion dark matter field generates nuclear EDM $d=d_0 \cos (\omega t)$ oscillating with the frequency $\omega= m_a c^2/\hbar$ . This EDM generates atomic EDM proportional to $\omega^2$. This effect is strongly enhanced in molecules since nuclei move slowly and do not produce as efficient screening of oscillating nuclear EDM as electrons do. An additional strong enhancement comes due to a small energy interval between rotational molecular levels. Finally, if the nuclear EDM oscillation frequency is in resonance with a molecular transition, there may be a significant resonance enhancement.