We show theoretical results for (gamma,pi(0)pi(0)) production on nucleons and nuclei in the kinematical region where the scalar isoscalar pipi 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.
Roca, L. Oset Báguena, Eulogio Vicente Vacas, Manuel José 2003 sigma meson in a nuclear medium through two pion photoproduction Nuclear Physics A 721 719 722
