I believe that is a power series expansion. The final answer should contain the exponential still since, we have to relate it to the path integral. I have just started learning the functional formalism and I wanted to know whether...
I'm studying QFT in the path integral formalism, and got stuck in deriving the Schwinger Dyson equation for a real free scalar field,
L=½(∂φ)^2 - m^2 φ^2
in the equation,
S[φ]=∫ d4x 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
Functional
Functional derivative
Path integral formulation
Quantum field theory
Series
Series expansion
Taylor
Taylor expansion
Taylor series