The Summation Transform

In the approximation of the spectrum as continuous, we can use the transform,

$$\sum_j \ \rightarrow \ \int d\omega_j D(\omega_j)$$ (5.1)

$$\begin{array}{\vert c\vert c\vert} \hline 1+\bar{n} \ \mbox{... ...g(\omega_j)^2 \bar{n}_j\gamma_j^{\dagger}\\ \hline \end{array}$$