Recent content by VietBrian

Does it mean vacuum is still vacuum if there is no source ?

Oh, yeah, it's now clearer for me ^^ Thank you!

Thank you very much! ^^ I had carefully read the book again. The vacuum-to-vacuum boundary conditions turned out to be \psi(t_i) = \psi_i and \psi(t_f) = \psi_f . :D And, are the operators you talk about above the field operators? \dfrac{\delta Z[J]}{\delta J(t_1)\ldots \delta...

Hello everyone :) I'm reading the book QFT - L. H. Ryder, and I don't understand clearly what are the generating functional Z[J] and vacuum-to-vacuum boundary conditions? Help me, please >"<