Comment on "Axion Dark Matter Coupling to Resonant Photons via Magnetic Field"

Abstract: A recent Letter, Phys. Rev. Lett. 116, 161804 (2016), claims that for typical dark matter axion search experiments using cylindrical haloscopes, the power gain depends on the relative position of a cavity with respect to the center of a solenoidal magnetic field due to different electric and magnetic couplings. We review this Letter and find a misinterpretation of the coordinate system. We correct this and see no dependence of the coupling strength on the cavity location and the electric and magnetic energies stored in a cavity mode are equal.