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Spin of a particle is a magnetic moment. Photon have spin-1, so why photon have not a magnetic moment because only 0-spin particles can not have a magnetic moment?

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    $\begingroup$ "Spin of a particle is a magnetic moment" Why do you think so? Just because particles with spin have a magnetic moment, that doesn't mean spin is that magnetic moment. $\endgroup$
    – ACuriousMind
    Nov 19, 2022 at 19:46
  • $\begingroup$ Welcome Khan. You might want to look at the closely related question Unlike electrons, photons don't have a magnetic moment despite having a spin. Why?. $\endgroup$ Nov 19, 2022 at 20:01
  • $\begingroup$ Do photons couple to photons? $\endgroup$ Nov 19, 2022 at 21:39
  • $\begingroup$ @Cosma-Zachos Yes, higher order two-photon processes do couple photons very weakly to photons. I believe the photon anomalous magnetic moment induced in hyperintense magnetic fields is due to triangular $\gamma\rightarrow \gamma\gamma$ photon splitting processes that are impossible for free photons, but can happen in the magnetic fields such as those around neutron stars. $\endgroup$ Nov 19, 2022 at 22:17
  • $\begingroup$ @David Baily. Of course, but do you seriously believe the OP is asking about induced loop couplings? There is no triangular effective coupling for vector couplings. $\endgroup$ Nov 19, 2022 at 22:56

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