It is unknown how electro weak breaking mechanism works, so, let us have a go at it? Well, i don't even know where to start, so, i will try to answer this with text, as I cannot understand the formulas provided on the net.

Seeing as how the photon has no mass, it would be attracted to the rest of the atom. It is held by force, but is not trapped. However the potential for it to get away is still there, as soon as there is another photon in the vicinity, the new photon will be attracted to the same things as the first photon, and then the photons will exhibit a 'draining' effect on the things holding it there. This means that eventually, photons will 'escape'.

Well, that is my stab at it at present - anyone else want to have a go?