Bethe-Salpeter equation confused

[Neitrino]

Dear PF,

Im reading something about bound states & there I one question.
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?

 

[azntoon]

The Bethe-Salpeter equation for a bound pair B describes the amplitude of a transition between a bound state and the vacuum. Conservation rules, such as energy and momentum conservation, still apply. The amplitude Phi (x,y) is related to the probability amplitude of the transition occurring. This equation is often used to describe the interactions between particles in atomic and molecular systems. You can find more information about the Bethe-Salpeter equation in books such as "Quantum Mechanics: A Textbook for Undergraduates" by Oleg V. Prezhdo and "Many-Body Quantum Theory in Condensed Matter Physics" by Henrik Bruus and Karsten Flensberg.