Medium effects on meson couplings and dilepton spectra

The πωπ coupling constant is calculated in a relativistic hadronic framework incorporating nucleons and Δ(1232) isobars. Medium modifications are included. The vertex is analyzed in context of the ω → π ⁰e⁺e^? and ρ ^a → π ^a e⁺e^? Dalitz decays in nuclear matter. A sizeable increase of the widths for these decays is found for invariant mass of dileptons in the range 0.2–0.5 GeV. This increase may help, among other medium effects, to explain the problem of the low-mass dilepton enhancement seen in relativistic heavy-ion collisions.