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In the functional integral approach to quantum field theory, we have
W[J] = ⟨0_{+}|0_{-}⟩_{J} = ∫ D[Φ] e^{iS + ∫ JΦ }
Can someone give me some insight into why this path integral is a vacuum-to-vacuum amplitude. How and also why does this path integral W[J] become a vev?
W[J] = ⟨0_{+}|0_{-}⟩_{J} = ∫ D[Φ] e^{iS + ∫ JΦ }
Can someone give me some insight into why this path integral is a vacuum-to-vacuum amplitude. How and also why does this path integral W[J] become a vev?