Let ⟨Ω| be the ground state of an interacting theory, just as Peskin & Schroeder(PS) describes on page 82 and page 213. On page 213 PS do the following
⟨Ω|ϕ(x)|λ→p⟩=⟨Ω|exp(+iPx)ϕ(0)exp(−iPx)|λ→p⟩=⟨Ω|ϕ(0)|λ0⟩exp(−ipx)|p0=E→p
In the above |λ0⟩ is an eigenstate of the full interacting hamiltonian H. The ket |λ→p⟩ is the boost of |λ0⟩ with momentum →p. Furthermore E→p=√p2+m2λ and →P|λ0⟩=0.
I assume PS used ⟨Ω|eiPx=⟨Ω|ei0x
in (1).
Is (2) true?
I thought ⟨0|eiPx=⟨0|ei0x where ⟨0| is the ground state of the free theory.
I hope I have provided enough info for the question to make sense.
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