The ρ spectral function in a relativistic resonance model

We calculate the spectral function Aρ of the ρ meson in nuclear matter. The calculation is performed in the low-density approximation, where the in-medium self-energy Σmed is completely determined by the vacuum ρ N forward scattering amplitude. This amplitude is derived from a relativistic resonance model. In comparison to previous nonrelativistic calculations we find a much weaker momentum dependence of Σmed, especially in the transverse channel. Special attention is paid to uncertainties in the model. Thus, we compare the impact of different coupling schemes for the RNρ interaction on the results and discuss various resonance parameter sets