Time it takes for a particle creation/annhilation (according to QFT)?

[triclon]

I am curious if quantum field theory says anything about how much time it takes for an interaction, or particle creation and annihilation, to take place. For example if I have a high energy photon, and it strikes an atomic nucleus and you get pair production forming an electron and positron. In the example, I am wondering what is the amount of time it takes to go from a photon to an electron and positron. Is there a certain amount of time for that process to occur or is it "instantaneous" where one moment you have a high energy photon and a nucleus at rest, and the next you have an electron and positron? I don't know enough about QFT to say. Perhaps the theory doesn't probe into the "process" of the interaction and can't say anything about the time it takes for it to occur? Or does theory have something to say?

 

[chrispb]

The interaction occurs at a single point in spacetime. However, keep in mind that you're really just saying that there's an amplitude at every point in spacetime for the interaction to take place.