Photons have no magnetic moment. You know this because the propagation of light is unaffected by the presence of the strongest magnetic fields we generate here on earth (which is several tesla.)
The article you're linking is not discussing the anomalous magnetic moment of the photon, but the electron. (Also muon and tau, but didactic QED texts usually focus on the electron.) You would expect the electron magnetic moment to be 2 \mu_B, where \mu_B is the Bohr magneton, if you calculated the magnetic moment purely from Dirac's Equation. However, due to coupling with particles winking in and out from vacuum fluctuations, the magnetic moment is slightly different than 2 \mu_B.
Photons have no magnetic moment. You know this because the propagation of light is unaffected by the presence of the strongest magnetic fields we generate here on earth (which is several tesla.)
The article you're linking is not discussing the anomalous magnetic moment of the photon, but the electron. (Also muon and tau, but didactic QED texts usually focus on the electron.) You would expect the electron magnetic moment to be 2 \mu_B, where \mu_B is the Bohr magneton, if you calculated the magnetic moment purely from Dirac's Equation. However, due to coupling with particles winking in and out from vacuum fluctuations, the magnetic moment is slightly different than 2 \mu_B.