pi^0 -> gamma gamma*, omega -> pi^0 gamma*, and rho -> pi gamma* decays in nuclear medium

Abstract

We calculate the medium modification of the pi-omega-rho vertex and analyze its significance for the pi^0 -> gamma gamma*, omega -> pi^0 gamma*, and rho -> pi gamma* 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 pi^0 -> gamma gamma* the effects of the Delta 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 omega -> pi^0 gamma* and rho -> pi gamma* we find a sizeable increase of the partial widths at virtualities of the photon in the range 0.3-0.6 GeV. The effect has direct significance for the calculation of dilepton yields from the Dalitz decays in relativistic heavy-ion collisions.