lant 0)})e^{-V^{(0)}(\Psi ^{(\leqslant 0)})+B^{(0)}(\Psi ^{(\leqslant 0)}, f, A)}, \end{aligned}$$\end{document}$$where $\documentclass[12pt]{minimal}
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                \begin{document}$$V^{(0)}$$\end{document}$ and $\documentclass[12pt]{minimal}
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                \begin{document}$$B^{(0)}$$\end{document}$ are, respectively, the effective potential and the effective source: they are defined by the conditions that $\documentclass[12pt]{minimal}
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                \begin{document}$$V^{(0)}(0)=0$$\end{document}$ and $\documentclass[12pt]{minimal}
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                \begin{document}$$B^{(0)}(0,f,A)=B^{(0)}(\Psi ,0,0)=0$$\end{document}$. The normalization constant $\documentclass[12pt]{minimal}
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