Does photon self energy contribute to the speed of light?

[Heidi]

TL;DR

Role of the self energy

Hi Pf

I read that in the light propagator there are loops of electrons. What would be the consequences if
we could switch them off (or neglect them)? would it modify the speed of the photons?

 

[vanhees71]

Since photons are described by a massless gauge field there's a Ward identity ensuring that quantum effects cannot generate a mass for photons. So photons stay massless.

The only exception is the Higgs mechanism. In the context of the photons it occurs in superconductors, where due to the formation of Cooper pairs of electrons a Higgs mechanism occurs for the corresponding in-medium QED. I.e., the photonic quasi-particles within a superconductor are massive.

 

[Vanadium 50]

What would be the consequences if we could switch them off

That could only be done consistently by turning off the photon-matter interaction, so such photons could neither be generated nor detected. It does not make sense to talk about the speed of such things.