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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?

Khan Ibrahim
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    "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. – ACuriousMind Nov 19 '22 at 19:46
  • 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?. – David Bailey Nov 19 '22 at 20:01
  • Do photons couple to photons? – Cosmas Zachos Nov 19 '22 at 21:39
  • @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. – David Bailey Nov 19 '22 at 22:17
  • @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. – Cosmas Zachos Nov 19 '22 at 22:56
  • @Cosma-Zachos No, I don't think the OP is asking about induced loop couplings, but you asked and I wasn't sure if it was rhetorically directed at the OP or an actual question. You are certainly correct that I should have left out the word "triangular". My mental image of photon-splitting ignored the 4th virtual photon from the magnetic field. – David Bailey Nov 19 '22 at 23:49
  • I think you will have a better understanding of the spin if you understand why spin is assigned to particles at the quantum level. It was necessary to do that so that the law of angular momentum conservation should hold as a law at the quantum level, Maybe my answer here helps https://physics.stackexchange.com/questions/540328/angular-momentum-of-a-single-particle/540529#540529 – anna v Nov 20 '22 at 05:46

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