rho ->pi pi decay in nuclear medium

We calculate the medium modifications of the rho pi pi vertex in a relativi stic hadronic framework incorporating nucleons and Delta (1232) isobars, an d find a substantial increase of the rho pi pi coupling, dominated by proce sses where the Delta is excited. The coupling depends significantly on the virtuality of the rho, which is related to analytic properties of the verte x function. We analyze the general case of a nonzero three-momentum of the rho with respect to the nuclear medium, and evaluate the resulting widths a nd spectral strength in the transverse and longitudinal channels for the rh o --> pi pi decay. These widths are used to obtain the dilepton yields from rho decays in relativistic heavy-ion collisions. (C) 2001 Elsevier Science B.V. All rights reserved.