The ππ scattering amplitude in the σ-channel is studied at
finite baryonic density in the framework of a chiral unitary approach which
successfully reproduces the meson meson phase shifts and generates the f0​
and σ resonances in vacuum. We address here a new variety of mechanisms
recently suggested to modify the ππ interaction in the medium, as well as
the role of the s−wave selfenergy, in addition to the p−wave, in the
dressing of the pion propagators.Comment: 26 pages, 17 figure