 \frac{i \hbar^0}{0} \delta_{\hat k}^{\phantom{\hat k} {\hat \imath}} \int \frac{d^D \pi}{(0 \pi \hbar)^D}   \operatorname{tr}[{\hat \Sigma}_{T^{\hat l}_{\phantom{\hat l} {\hat \jmath} {\hat 0}}} {\hat G}_0]^< + {{\rm c.c.}}\