Formula_3484

\[\begin{gathered}\varphi(s)=\operatorname{Eexp}[i s \xi(t, \varepsilon)]= \\=\sum_{l=0}^{\infty} \frac{(i s)^{l}}{l !} \int_{0}^{\varepsilon} f_{l}\left(\varepsilon_{1}, \varepsilon_{2}, \ldots, \varepsilon_{l} ; t\right) d \varepsilon_{1} d \varepsilon_{2} \ldots d \varepsilon_{l} .\end{gathered}\]