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Electromagnetic Interaction  [T]

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Photon

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The photon is associated with he electromagnetic interaction.  The photon has zero mass and zero electric charge.  It interacgts with any particle that carries charge, with a strength that increases with the magnitude of the charge. [1]

Thus the photon couples stronger to the up quark (charge +2/3) thatn to the down quark (charge -1/3), and it does not couple at all to neutrinos or other photons.

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The electromagnetic interaction is shown this way in a Feynman diagram :

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