The σ meson in a nuclear medium through two pion photoproduction

We present theoretical results for (γ,π0π0) production on nucleons and nuclei in the kinematical region where the scalar isoscalar ππ amplitude is influenced by the σ 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 σ pole to lower masses and widths as the nuclear density increases.