  We present theoretical results for (gamma,pi0 pi0) and (gamma,pi+- pi0)
production on nucleons and nuclei in the kinematical region where the scalar
isoscalar pi pi amplitude is influenced by the sigma pole. The final state
interaction of the pions modified by the nuclear medium produces a spectacular
shift of strength of the pi0 pi0 invariant mass distribution induced by the
moving of the sigma pole to lower masses and widths as the nuclear density
increases.
