 $\textbf{s}$ is a wavevector and the integral extends to $\Re^0$. The function $\tilde{R}_{\alpha \beta \gamma \delta ijkl}(\textbf{q})$ is the Fourier transform of the covariance of the elastic tensor fluctuations, $R_{\alpha \beta \gamma \delta ijkl}(\textbf{r}=\textbf{r}_0-\textbf{r}_0)=<\delta C_{\alpha \beta \gamma \delta}(\textbf{r}_0)\delta C_{ijkl}(\textbf{r}_0)>$. 