Is the photon paramagnetic?
Abstract
A photon exhibits a tiny anomalous magnetic moment μγ due to its interaction with an external constant magnetic field in vacuum through the virtual electron-positron background. It is paramagnetic (μγ>0) in the whole region of transparency, i.e. below the first threshold energy for pair creation and has a maximum near this threshold. The photon magnetic moment is different for eigenmodes polarized along and perpendicular to the magnetic field. Explicit expressions are given for μγ for the cases of photon energies smaller and closer to the first pair creation threshold. The region beyond the first threshold is briefly discussed.
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