Effect of the axion halo on bound electrons

Effects of the hypothetical galactic axion halo on electrons are described in nonrelativistic terms. The principal effect is a spin-dependent force (ma 2/2F)a, where a is the axion field, ma the axion mass, and F-1 the interaction strength. A magnetic-field-dependent force and a velocity-dependent spin precession also occur. The current thus generated in a ferromagnet depends on ordinary considerations of atomic binding, band structure, effective mass, and electron scattering. It is negligible in ferrites. A substantial current is predicted in pure d-electron metallic ferromagnets at helium temperature. Implications for halo probes are touched upon. © 1985 The American Physical Society.