You need to be careful with what you say here. Although i get the point you are making, it needs to be said that loops in QED and QCD correspond to self-energy terms. Indeed a short-lived electron positron pair can be created and "killed" shortly after. You do not need loops for that though since this process happens constantly in the vacuum, ie vacuum fluctuations of QFT. When enough energy is available this virtual pair can become real and "long-living".gptejms said:Guys,I was referring to the loop in a Feynman diagram which is a virtual process(!)--all I said was that the short-lived electron-positron pair in such a scenario may be given the kind of interpretation I gave above.
Like i stated before : i see no reason what so ever to keep on making a difference between a positron and a hole since they are fundamentally seen exactly the same in QFT. Like in this post with them loops, i had to mention the concept of self energy, expressing the fact that a particle in QFT does NOT exist alone, although it can be considered to be independent of other particles.