散乱理論
⟨ k + q | T | k ⟩ = ⟨ k + q | V | k ⟩ + ∫ ⟨ k + q | V | k + q ′ ⟩ ⟨ k + q ′ | V | k ⟩ ( k 2 − | k + q ′ | 2 ) d 3 q ′ + ⋅ ⋅ ⋅ {\displaystyle \langle \mathbf {k} +\mathbf {q} |T|\mathbf {k} \rangle =\langle \mathbf {k} +\mathbf {q} |V|\mathbf {k} \rangle +\int {\langle \mathbf {k} +\mathbf {q} |V|\mathbf {k} +\mathbf {q} '\rangle \langle \mathbf {k} +\mathbf {q} '|V|\mathbf {k} \rangle \over {(k^{2}-|\mathbf {k} +\mathbf {q} '|^{2})}}d^{3}q'+\cdot \cdot \cdot }
T演算子は、