A real photon self-energy Feynman diagram

On May 12, 2021 we analyzed the electron self-energy and concluded self-energy has no effect on a free (real) electron.

Let us consider a real ("free") photon flying in a vacuum. The photon self-energy means the hypothetical effect of photon conversion into a virtual electron-positron pair mid-flight.

                        e- virtual

                     _____

                   /           \

      ~~~~~                ~~~~~     real photon

                   \______/

                        e+ virtual

Above we have a Feynman diagram of photon self-energy.

If the virtual pair would possess positive rest mass, then the flight of the photon would be slowed down below the speed of light. We conclude that the entire energy of the pair must be kinetic. Then the flight of the pair is probably described by the massless Klein-Gordon equation, just like the flight of the photon.

We do not believe that "empty space" can change the phase of the photon. Conclusion: self-energy has no effect on real photon propagation.

Just as in the case of electron self-energy, it is unclear what the Feynman diagram above means. If the photon proceeds for 1 meter, how many times does it get converted into a virtual pair?

There may exist some kind of polarization of vacuum around the photon. We have suggested in this blog that the photon itself might be a rotating virtual electron-positron pair.