Constraints on spin-dependent exotic interactions between electrons at the nanometer scale

Abstract

New laboratory constraints are obtained on exotic interactions between electrons through pseudoscalar or pseudovector coupling by analyzing a recent measurement of the magnetic dipole-dipole interaction between two iron atoms at the nanometer scale. The analysis imposes the strongest bounds on the pseudovector coupling constant $({g}_{A}^{e}{)}^{2}/4\ensuremath{\pi}\ensuremath{\hbar}c$ between electrons for exchange bosons heavier than 1 eV. Even with the counterpart of electron-positron interaction considered by assuming $CPT$ invariance, the constraints are still the most stringent for bosons in the mass range from 1 eV to 20 eV. The constraints on the pseudoscalar coupling constant $({g}_{p}^{e}{)}^{2}/4\ensuremath{\pi}\ensuremath{\hbar}c$ are only stronger than the limits derived from the trapped-strontium-ion experiment for exchange bosons heavier than 0.14 eV. Furthermore, a new experiment for more stringent constraints is proposed by measuring the interaction between one iron atom and multiple Holmium atoms.