ω→π0γ∗, ρ→πγ∗, and π0→γγ∗ decays in nuclear medium

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