Bethe-Salpeter equation confused

1. Nov 27, 2005

Neitrino

Dear PF,

The Bethe-Salpeter equation for a bound pair B deals with the amplitude:

Phi (x,y)=<0|TPsi(x)Psi_bar(y)|B>, |B> is a bound pair state, <0| vacuum...what i missunderstand how it can be the transition between some bound state and vacuum? What about conseravation rules..
Or generally what amplitude is it what transition does it describe?

If I even wright something bad pls correct me.
Thks

Any books where this is described?