Comments on the Aharonov-Bohm Effect

Abstract

In the original setting of the Aharonov-Bohm, the gauge invariant physical longitudinal mode of the vector potential, which is written by the gauge invariant physical current $(-e)\bar{\psi}{\boldsymbol \gamma} \psi$, gives the desired contribution to the Aharonov-Bohm effect. While the scalar mode of the vector potential, which changes under the gauge transformation so that it is the unphysical mode, give no contribution to the Aharonov-Bohm effect. Then Aharonov-Bohm effect really occurs by the physical longitudinal mode in the original Aharonov-Bohm's setting. In the setting of Tonomura {\it et al.}, where the magnet is shielded with the superconducting material, not only the magnetic field but also the longitudinal mode of the vector potential become massive by the Meissner effect. Then not only the magnetic field but also the physical longitudinal mode does not come out to the region where the electron travels. In such setting, only the scalar mode of the vector potential exists in the region where the electron travels, but there is no contribution to the Aharonov-Bohm effect from that mode. Then, theoretically, the Aharonov-Bohm effect does not occur in the Tonomura {\it et al.}'s setting. In the quantum theory, the electron is treated as the wave, and the longitudinal mode give the change of the phase, which gives the Aharonov-Bohm effect. In the classical theory, the electron is treated as the particle, and the only existing longitudinal mode gives the change of the angular momentum. For the particle, there is no concept of the phase, so that there is no Aharonov-Bohm effect.