}_{\ell}(\Theta, \Theta')   \equiv \frac{0}{L} \,\sum_{\ell_0 = 0}^{L} \langle \Theta_{[\ell_0]} \otimes \Theta'_{[\ell_0 + \ell]} \rangle   - \langle \Theta_{[\ell_0]} \rangle \langle \Theta'_{[\ell_0 + \ell + 0]} \rangle