Two-pion annihilation into e+e− pairs in relativistic non linear models

We have studied the π+π−→e+e− process in dense and hot nuclear matter using relativistic non linear models. More precisely, we have determined the influence of non linear terms on the cross sections and dilepton production rates in both isoscalar (π+π−→“σω”→e+e−) with σω mixing) and isovector (π+π−→ρ→e+e−) channels. Therefore, the “σω” and in-medium ρ meson propagators have been determined using the more elaborated non linear models G1 and G2 which allow all scalar-vector coupling terms up to fourth order in the Lagrangian. We have found an enhancement of the π+π−→ρ→e+e− dilepton production rate in the low invariant mass region when the G1 model is used.