In a simplified model one can assume that a vacuum fluctuation creates an electron-positron pair (i.e. positronium) for a short time. Let's assume a photon interacts with this vacuum fluctuation.
Is it possible, that the average magnetic moment $m$ of the positronium in the magnetic field of the photon is non-zero? Is it possible to determine the value?
(That the average polarization is non-zero is quite clear to me.)
