  We present theoretical results for $(\gamma, \pi^0 \pi^0)$ 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 two pion invariant mass distribution induced by the moving of
the $\sigma$ pole to lower masses and widths as the nuclear density increases.

Nuclear Theory