# Self-energy for two correlators

1. Sep 10, 2015

Imagine I want to calculate the INTERACTING single particle Green function in a model:

\begin{eqnarray}
G(t-t')=\langle Td(t)d^{\dagger}(t')\rangle
\end{eqnarray}

We know from Dyson equation that this is:\\
\begin{eqnarray}
G=G_{0} + G_{0}\Sigma G
\end{eqnarray}
Where $\Sigma$ is the self-energy. My question is, if we want to calculate the correlator :\\
\begin{eqnarray}
g(t-t')=\langle Td(t)^{\dagger}d(t')\rangle
\end{eqnarray}
Does the self-energy $\Sigma$ change for this correlator? In my intuition it shouldnt, but maybe I am wrong... Thanks!

2. Sep 10, 2015

Oh and by the way I forgot, does Dyson equation apply to this correlator as well ($g(t-t')$)? (Even not being the definition of a Green function, can this infinite series be hold in a correlator like that when we do perturbation theory? )