Exact Optical Dielectric Function of a Nearly Homogeneous Solid

Based on an exactly solvable model of a nearly homogeneous solid (jellium+phonons), we compute the optical dielectric function exactly at zero temperature in any number of spatial dimensions. It is argued as we have done elsewhere, that the answer for the optical dielectric function we obtain is in fact the exact answer for a real nearly homogeneous solid in the same limit in which RPA itself is exact.