I can't find this in any textbook, so I must not understand something about it. What is the Lagrangian of a photon? Would it be just h*nu?
Which part ofOK, then how does one calculate the action (S) for the amplitude of a photon?
was unclear? You need to specify exactly what it is you are trying to do.There is no such thing as the lagrangian of a photon. Photons are quantum excitations of the electromagnetic field,
You don't. You compute the action of the electromagnetic field and correlation functions (essentially amplitudes) between different excitations of the field.So if a photon has no Lagrangian, how does one calculate the action, amplitude, probability, etc. for a photon?