We calculate the modification of a rho meson in nuclear matter through its coupling to resonance-hole states. Starting from a recently proposed model, we include all four star resonances up to 1.9 GeV. In contrast to previous works, we include not only resonances that couple to the rho in a relative p-wave, but also those that couple to an s-wave state. In addition, we solve the equation for the rho spectral function self-consistently. We find that s-wave resonances affect the in medium spectral function of the rho strongly. In the transverse channel the rho meson is, especially at non zero momentum, completely washed out and can in the presence of nuclear matter no longer be viewed as a resonant excitation of the vacuum. Instead, our model shows a continuum of possible excitations with the quantum numbers of a transversely polarized rho. In the longitudinal channel, however, the rho retains its resonant character in our calculation. As a consequence of the self-consistent treatment we also find a strong enhancement of the widths of the included nucleon resonances in medium. * Work supported by BMBF and GSI Darmstadt.

We study the in-medium properties of mesons (π, η, ρ) and baryon resonances in cold nuclear matter within a coupled-channel analysis. The meson self energies are generated by particle-hole excitations. Thus multi-peak spectra are obtained for the mesonic spectral functions. In turn this leads to medium-modifications of the baryon resonances. Special care is taken to respect the analyticity of the spectral functions and to take into account effects from short-range correlations both for positive and negative parity states. Our model produces sensible results for pion and ∆ dynamics in nuclear matter. We find a strong interplay of the ρ meson and the D 13 (1520), which moves spectral strength of the ρ spectrum to smaller invariant masses and leads to a broadening of the baryon resonance. The optical potential for the η meson resulting from our model is rather attractive whereas the in-medium properties modifications of the S 11 (1535) are found to be quite small.

We calculate the spectral function of the ω meson in nuclear matter at zero temperature by means of the low-density theorem. The ωN forward scattering amplitude is calculated within a unitary coupled-channel effective Lagrangian model that has been applied successfully to the combined analysis of pion-and photon-induced reactions. While the peak of the ω spectral distribution is shifted only slightly, we find a considerable broadening of the ω meson due to resonance-hole excitations. For ω mesons at rest with respect to the surrounding nuclear medium, we find an additional width of about 60 MeV at saturation density.

We calculate the spectral function A ρ of the ρ meson in nuclear matter. The calculation is performed in the low density approximation, where the in-medium self energy Σ med is completely determined by the vacuum ρ N forward scattering amplitude. This amplitude is derived from a relativistic resonance model. In comparison to previous non-relativistic calculations we find a much weaker momentum dependence of Σ med , 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 RN ρ interaction on the results and discuss various resonance parameter sets.

We estimate the resonance coupling strength f RN ω and f RN ρ from a Vector Meson Dominance (VMD) analysis. The isoscalar and isovector part of the photon coupling are obtained separately from helicity amplitudes. The reliability of this approach is tested by comparing VMD predictions for f RN ρ with values obtained from fitting the hadronic decay widths into N ρ. A reasonable agreement is found, but VMD tends to underestimate the coupling constants. In order to confirm consistency with experimental data, we calculate the crosssections for photon-and pion induced reactions within a Breit-Wigner model. Finally, we study how the properties of ω mesons in nuclear matter are affected from the excitation of resonance-hole loops. For an ω at rest, we find a broadening of about 40 MeV, while at higher momenta the effect of resonance excitations is reduced.