I'm studying QFT in the path integral formalism, and got stuck in deriving the Schwinger Dyson equation for a real free scalar field,(adsbygoogle = window.adsbygoogle || []).push({});

L=½(∂φ)^2 - m^2 φ^2

in the equation,

S[φ]=∫ d^{4}x L[φ]

∫ Dφ e^{i S[φ]} φ(x1) φ(x2) = ∫ Dφ e^{i S[φ']} φ'(x1) φ'(x2)

Particularly, it is in the Taylor series expansion of the functional exponential

e^{i S[φ']}=e^{i S[φ+iα]} . Can anybody please tell me about the expansion? I have searched and haven't found anything quite helpful on the net. Thank you.

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# A Taylor series expansion of functional

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