# Tag Info

$|\Omega\rangle$ is the vacuum of the full interacting theory and $|0\rangle$ is the vacuum of the free theory. They are related in the following way $$|\Omega\rangle = \lim_{T\rightarrow(1-i\epsilon)\infty} (e^{-iE_0(T+t_0)}\langle \Omega|0\rangle)^{-1}e^{-iHT}|0\rangle$$ and the correlators  \langle \Omega|\phi(x_1)\phi(x_2)...\phi(x_n)|\Omega\rangle = ...