Medium

We calculate the medium modification of the πωρ vertex and analyze its significance for the π0 → γγ∗, ω → π0γ∗, and ρ → πγ∗ decays in nuclear matter. We use a relativistic hadronic approach at zero temperature and in the leading-density limit, and consider decays of particles at rest with respect to the medium. It is shown that for the π0 → γγ∗ the effects of the ∆ isobar cancel almost exactly the effects of the nucleon ph excitations, such that the net medium effect is small. On the contrary, for the decays ω → π0γ∗ and ρ → πγ∗ we find a sizeable increase of the partial widths at virtualities of the photon in the range 0.3−0.6GeV. The effect has direct significance for the calculation of dilepton yields from the Dalitz decays in relativistic heavy-ion collisions.